WO2025242558A1 - Germanane derivatives - Google Patents

Abstract

The present invention relates to new sulfur-containing organic ligand-terminated forms of germanane that are stable against air oxidation, to a synthetic route for the preparation of said germanane derivatives and to the use of said derivatives as stimuli responsive materials.

Description

GERMANANE DERIVATIVES

FIELD OF THE INVENTION

The present invention relates to 2D materials, in particular to 2D-thiolated germanane derivatives, to a process for the synthesis of said derivatives and to the use of said derivatives as stimuli-responsive materials.

BACKGROUND OF THE INVENTION

During the last decade, two-dimensional (2D) monoelemental materials akin to graphene, commonly referred to as Xenes and whose structures are composed of atomthick monolayers held together by van der Waals forces, have emerged as a new family of semiconducting Inorganic 2D Materials (i2DMs) owing to their promising physicochemical features ascribed to them [T. Wang, et al., Advanced Functional Materials, 30(36), 2002885], Succeeding graphene, the first generation of Xenes arose with the aim to expand the family of 2D monoelemental materials belonging to the Group IVA, resulting in silicene (2D-Si), germanene (2D-Ge), stanene (2D-Sn) and plumbene (2D-Pb) [J. Munoz, Advanced Materials, 36(8), 2305546], Particular attention has been devoted to the predicted properties of 2D-Ge as unconventional semiconducting i2DMs due to its large band-gap and easily tailored optoelectronic properties [N. Liu, et al., Small, 15(32), 1805147],

To date, ligand-terminated 2D-Ge derivatives have been mainly obtained through a specific type of topochemical transformation of Zintl-phase CaGe2 under harsh conditions [S. Ng, et al., Advanced Materials, 2022, 35(7), 2207196], For example, the immersion of CaGe2 into concentrated halogen acids (HX) has led to the mass production of H-terminated 2D-Ge (2D-GeH), i.e. germanane, being nowadays the only commercially available Xene [T. Giousis, et al., Angewandte Chemie, 2021 , 133(1), 364- 369], However, the almost unexplored chemical reactivity of 2D-GeH has hindered its direct functionalization with alternative functional R groups, being the field limited to the use of such a topochemical approach for the synthesis of R-terminated 2D-Ge (2D-GeR) from the Zintl phase employing alkyl halides (RX). Albeit tedious, the terminal R ligand becomes covalently bonded to each Ge atom. In 2019, Hartman and co-workers described a tedious functionalization procedure for the direct modification of 2D-GeH with RX using strong bases as alkali metal arenides [T. Hartman, et al., Angewandte Chemie, 131 (46), 16669-16674], More recently, Munoz and co-workers demonstrated the suitability of the thiol-ene click chemistry for the direct covalent functionalization of allyl-terminated 2D-Ge (viz. 2D-GeCHCHCH2) with different thiol-rich moieties via Ge-C- S bond formation [J. Munoz, et al., Advanced Functional Materials, 2022, 34(45), 2206382], However, the large bond distance between the moiety and the Xene reduces the proper tunabilitily of the material.

Amongst the limitless variety of ligands that can be custom-designed and synthesized with predictable functionalities, the integration of active molecular components (/.e., stimuli-responsive molecules) onto i2DMs is very appealing to tune and modulate the physicochemical properties of materials on-demand, otherwise unattainable for their pristine counterparts [Y. Zhao, et al., Advanced Optical Materials, 7(16), 1900286], The main challenge in the field relies on making 2D-Ge functional for task-specific applications while having increased stability and reduced air reactivity.

Thus, there is a need for stable ligand-terminated forms of 2D-Ge, which may be obtained by simple functionalization methods.

SUMMARY OF THE INVENTION

The inventors have unexpectedly found a family of ligand-terminated forms of 2D-Ge that are stable against air oxidation. Moreover, the inventors have found a synthetic route to functionalize 2D-GeH for task-specific applications by a direct covalent molecular functionalization of commercially available 2D-GeH. The obtained ligand-terminated germanane derivatives can be used as stimuli responsive materials, such as to perform different binary logic operations.

Thus, in the first aspect, the present invention relates to a 2D germanane derivative comprising units of formula (I):

Ge-R (I) wherein R is a sulfur-containing organic ligand covalently bound through its sulfur atom (or one of its sulfur atoms) to germanium atoms as defined in the claims. In the second aspect, the invention relates to a process for the preparation of a 2D germanane derivative according to the first aspect, wherein the process comprises reacting 2D germanane with a compound of formula (II):

R-H (II) wherein R is as defined in the first aspect, wherein the reaction is carried out in the absence of oxygen or wherein the oxygen concentration is lower than 5% by volume.

In a third aspect, the invention relates to the use of a 2D germanene derivatives according to any one the first aspect for the applications defined in the claims.

DESCRIPTION OF THE FIGURES

Figure 1 shows the results of material characterization of 2D-GeFce. a) FTIR spectra of pristine 2D-GeH and 2D-GeFce, highlighting the main shifts observed (insets), b) FTIR spectra of 2D-GeFce and isolated Fce-SH. c) XPS main core level spectra of Ge 3d, S 2p and Fe 2p recorded for pristine 2D-GeH (top) and 2D-GeFce (bottom), d) XPS core level spectra of Ge 3d for pristine 2D-GeH (top) and 2D-GeFce (bottom) after 15 days under air exposure (Note: XPS measurements were run on an FTO substrate, and therefore a new contribution peaked at 26.0 eV is observed (*), which correspond to Sn 4d). e) UV-vis spectra of pristine 2D-GeH and 2D-GeFce with f) the corresponding Tauc plots displaying the obtained optical band gaps.

Figure 2 shows the FTIR spectra of 2D-GeFcn, 2D-GePh, 2D-GeCD and L-2D-GeCys with the respectively isolated thiolated molecules.

Figure 3 shows the XPS core level spectra of Ge 3d for 2D-GeFcn, 2D-GePh and 2D- GeCD. Since the measurements were run on an FTO substrate, the spectrum of the bare FTO substrate is also shown for comparison.

Figure 4 shows the Tauc plots displaying the obtained optical band gaps for 2D-GeFcn, 2D-GePh, 2D-GeCD and L-2D-GeCys.

Figure 5 shows the chiroptical properties L-2D-GeCys and D-2D-GeCys. CD spectra of a) isolated L- and D-cys and b) pristine 2D-GeH, L-2D-GeCys and D-2D-GeCys. Figure 6 shows the molecule-programmable properties of 2D-GeFce: Electrical Input- Optical Output, a) Excitation (inset) and emission fluorescence spectra recorded for pristine 2D-GeH and 2D-GeFce. b) Spectro-electrochemical emission spectra of 2D- GeH (left) and 2D-GeFce (right) using oxidation (+0.6 V) and reduction (-0.2 V) bias potentials, c) Time vs. fluorescence intensity experiment for 2D-GeFce by monitoring the emission band at 452 nm through modulating the bias potential from +0.6 V (2D-GeFce — > [2D-GeFce]⁺) to -0.2 V ([2D-GeFce]⁺ — > 2D-GeFce) in pulses of 90 sec, with d) the resulting normalized fluorescence spectra with the ON/OFF cycles. Spectro- electrochemical measurements were run in a three-electrode configuration cell of quartz filled with 0.1 M PBS (pH 7.2) as the electrolyte.

Figure 7 shows the molecule-programmable properties of 2D-GeFce: Electrical Input- Electrical Output. Cyclic voltammograms over 50 cycles for a) pristine 2D-GeH and b) 2D-GeFce. c) 2D-GeFce CVs at different scan rates (0.01 , 0.05, 0.1 , 0.25, 0.5, 0.75 and 1 V s^-1), and d) current vs. scan rate plots, e) Bode plot displaying capacitance vs. logarithm of frequency at different oxidation (+0.26 V) and reduction (-0.2 V) bias potentials for pristine 2D-GeH (inset) and 2D-GeFcs, with f) its respectively 12 successive capacitance redox cycles. Electrochemical experiments were run in a three-electrode configuration cell filled with 0.1 M PBS at pH 7.2.

Figure 8 shows the electrochemical performance of 2D-GeFcn: a) Cyclic voltammograms of pristine 2D-GeH and 2D-GeFcn, displaying the inherent Fe²⁺/Fe³⁺ redox process, b) Capacitance vs. frequency spectra of 2D-GeFcn at different oxidation (+ 0.36 V) and reduction (- 0.2 V) bias potentials, and c) stability test after 12 successive redox cycles.

Figure 9 shows the enantiodiscrimination ability of 2D-GeCD towards a chiral target as Trp: Fluorescence spectra of pristine 2D-GeH (a-b) and 2D-GeCD (c-d) in absence and presence of L-Trp (a,c) and D-Trp (b,d) at different concentrations (T 10^-8 M and T 10'⁵ M). e) Calibration curve obtained from the fluorometric data (spectra c-d) showing the different sensitivity (slopes) of 2D-GeCD towards different Trp enantiomers.

Figure 10 shows the ability of 2D-GePh for sensing carbon nanoparticles (e.g., carbon dots, CDs) via TT-stacking interactions: a) Nyquist plots and the resulting calibration curve (b) from the exposure of 2D-GePh towards different concentration of CDs (0.01 , 0.02, 0.03, 0.04 and 0.05 mg-mL’¹).

DETAILED DESCRIPTION OF THE INVENTION

2D qermanane derivatives of the invention

In the first aspect, the present invention relates to a 2D germanane derivative comprising units of formula (I):

Ge-R (I) wherein R is a sulfur-containing organic ligand covalently bound through its sulfur atom (or one of its sulfur atoms) to germanium atoms.

In the context of the present invention, the term “sulfur-containing organic ligand” refers to any organic molecule as defined below bonded to at least one sulfur atom which may form a covalent thioether bond with a germanium atom (Ge-S-). The sulfur atom originates from a thiol group (-SH) which loses its hydrogen atom upon bonding to the Ge atom.

The term “organic molecule” refers to any chemical compound that contains carbon and hydrogen atoms. Said compounds may contain rings and/or straight or branched chains, they may be saturated or may contain unsaturations or be aromatic. Said compounds may contain one or more N, O and/or S atoms. In particular, the organic molecule is selected from a C1-C20 alkyl group optionally substituted by oxygen or nitrogen containing groups or atoms, a monocyclic or polycyclic aromatic or heteroaromatic ring system optionally substituted by oxygen or nitrogen containing groups or atoms. Preferably the alkyl and monocyclic or polycyclic aromatic or heteroaromatic ring system is substituted by a stimuli-responsive derivative. Examples of stimuli-responsive derivatives are those compounds which exhibit responsiveness to external stimuli, in particular light- responsive (such as azobenzene, stilbene, spiropyran or diarylenethene), redox responsive (such as tetrathiafulvalene, ferrocene (and other metallocenes), anthraquinone, benzodifuran, and viologen), pH-responsive (such as carboxylic acids, phosphoric acids, sulfonic acids, boronic acids, amino acids, amines, pyridines, imidazoles, piperazines, hydrazones, pyrrolidines, and morpholines), (bio-)chemical responsive (enzymes, amino acids, aromatic rings, DNA and RNA fragments), and supramolecular-responsive (such as macrocycles including cyclodextrin, curcubit[n]uril, calix[n]arenes, and pillar[n]arenes], as disclosed in [J. Munoz, Advanced Materials, 2024, 36(8), 2305546],

The present invention relates to a 2D germanane derivative comprising units of formula (I):

Ge-R (I) wherein

R is a sulfur-containing ligand covalently bound through its sulfur atom (or one of its sulfur atoms) to germanium atoms and which is selected from the group consisting of: a) -S-(CH2)n-ferrocenyl wherein n is from 1 to 20, b) a thiolated cyclodextrin which is covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin and which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; - Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-Ci-Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl-NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl, c) -S-A, wherein A is a 6- to 14-membered monocyclic or polycyclic aromatic or heteroaromatic ring system which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; -Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-C1- Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl-NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl, and

In the context of the present invention, the term “2D” or “two-dimensional” refers to materials in the form of sheets having a smallest dimension, i.e. the thickness, of less than 100 nm, preferably from 5 to 10 nm.

The term “germanene” is a 2D material made up of a single layer of germanium atoms, which has a nearly flat honeycomb structure in the form of slightly buckled sheets, unlike graphene which is totally planar. Germanene has a crystal structure consisting of an atom-thick monolayer network held together by van der Waals forces.

Adding covalently bonded hydrogen atoms on both sides of germanene, as defined above, leads to “germanane” also named as “hydrogen-terminated germanene” or “GeH”, which is also a 2D material. Therefore, this material can also be named as “2D germanane”, “2D hydrogen-terminated germanane” or “2D GeH”.

In the germanane derivatives of the present invention, at least 2 of the hydrogen atoms of germanane have been replaced with variable sulfur-containing ligands which are covalently bonded to the Ge atoms by a S atom of said sulfur-containing ligands, preferably from 20% to 30% of the hydrogen atoms of germanane have been replaced with variable sulfur-containing ligands which are covalently bonded to the Ge atoms by a S atom of said sulfur-containing ligands. The germanane derivatives of the present invention are also 2D materials.

In the germanane derivatives of the present invention R is a sulfur-containing ligand covalently bound through its sulfur atom (or one of its sulfur atoms) to germanium atoms and which is selected from the group consisting of: a) -S-(CH2)n-ferrocenyl wherein n is from 1 to 20, b) a thiolated cyclodextrin which is covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin and which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; - Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-Ci-Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl-NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl, c) -S-A, wherein A is a 6- to 14-membered monocyclic or polycyclic aromatic or heteroaromatic ring system which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; -Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-C1- Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl-NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl, and

In one embodiment, R is a -S-(CH2)n-ferrocenyl wherein n is from 1 to 20, preferably from 5 to 12, more preferably from 6 to 11 , even more preferably 6 or 11.

The term “ferrocenyl” refers to the radical of ferrocene (i.e. a ferrocene from which a hydrogen atom has been removed), which is a complex consisting of two cyclopentadienyl rings sandwiching a central iron atom. Ferrocenyl is a redox-responsive molecule.

In the -S-(CH2)n-ferrocenyl ligand, the ferrocene ring is attached to the -(CH2)n-S- moiety by any of the carbon atoms of the ferrocene.

In another embodiment, R is a thiolated cyclodextrin which is covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin and which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; -Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-Ci-C₆ alkyl, -NH₂ and -NH-CI-C₆ alkyl; and -Ci-C₆ alkyl-NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl. Preferably, the thiolated cyclodextrin is unsubstituted.

The term “alkyl” refers to a straight or branched hydrocarbon chain radical consisting of carbon and hydrogen atoms, containing no unsaturation, having the indicated number of carbon atoms, and which is attached to the rest of the molecule by a single bond, e. g., methyl, ethyl, n-propyl, /-propyl, n-butyl, f-butyl or n-pentyl.

The term “alkoxy” refers to a radical of the formula -ORa where Ra is an alkyl radical as defined above, e. g., methoxy, ethoxy or propoxy.

The term “cyclodextrin” refers to a cyclic oligosaccharide, consisting of a macrocyclic ring of 6 to 8 glucose subunits joined by a-1 ,4 glycosidic bonds. In particular, a- cyclodextrin has 6 glucose subunits, p-cyclodextrin has 7 glucose subunits and y- cyclodextrin has 8 glucose subunits, as shown below, preferably a p-cyclodextrin.

Cyclodextrins are supramolecular-responsive molecules. a-cyclodextrin P-cyclodextrin

The term “thiolated cyclodextrin” refers to a cyclodextrin as previously defined wherein one or more or the OH groups, including primary and secondary OH groups, have been replaced by a SH group. In one embodiment, all the primary OH groups have been replaced by a SH group as in the thiolated cyclodextrin structures depicted below and named as thiolated a-cyclodextrin, thiolated p-cyclodextrin and thiolated y-cyclodextrin. In another embodiment, all the OH groups of the cyclodextrin (primary and secondary OH groups) have been replaced by a SH group. Preferably, R is an unsubstituted thiolated cyclodextrin covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin.

In a more preferred embodiment, the thiolated cyclodextrin is selected from the group consisting of the thiolated a-cyclodextrin, the thiolated p-cyclodextrin and the thiolated y- cyclodextrin depicted below, preferably the thiolated p-cyclodextrin depicted below, i.e. a thiolated a-cyclodextrin, thiolated p-cyclodextrin and thiolated y-cyclodextrin, wherein all the primary OH groups of the corresponding cyclodextrin have been replaced with a

SH group. thiolated a-cyclodextrin thiolated p-cyclodextrin thiolated y-cyclodextrin In the germanane derivative of the invention, the thiolated cyclodextrin is covalently bonded to the Ge atom by any of the S atoms of the thiolated cyclodextrin, preferably by an S atom of a primary thiol, i.e. a thiol wherein the S atom is linked to a -CH2- moiety.

In a more preferred embodiment, R is wherein * represents the attachment point to the Ge atom.

In another embodiment, R is a -S-A group, wherein A is a 6- to 14-membered monocyclic or polycyclic aromatic or heteroaromatic ring system.

In the context of the present invention, the term “aromatic ring system” refers to stable substituted or unsubstituted unsaturated mono- or polycyclic hydrocarbon ring systems, having preferably 6 to 14 carbon atoms, comprising at least one ring satisfying the Huckel rule for aromaticity. Examples of aromatic ring systems include, but are not limited to, phenyl, indanyl, indenyl, naphthyl, phenanthryl, and anthracyl.

In the context of the present invention, the term “heteroaromatic ring system” refers to stable substituted or unsubstituted unsaturated mono-heterocyclic or polyheterocyclic moieties having preferably 6 to 14 carbon atoms, comprising at least one ring satisfying the Huckel rule for aromaticity and comprising one or more heteroatoms in the ring, such as N, O and/or S. Examples of heteroaromatic ring systems include, but are not limited to, pyridyl, quinolinyl, dihydroquinolinyl, isoquinolinyl, quinazolinyl, dihydroquinazolyl, and tetrahydroquinazolyl. The aromatic and heteroaromatic ring systems may be optionally substituted by one or more substituents selected from the group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; -Ci- Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-Ci-Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl-NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl.

Preferably, the aromatic and heteroaromatic ring systems are unsubstituted.

In a preferred embodiment, R is -S-phenyl.

Aromatic and heteroaromatic ring systems have chemical responsive ability.

In another embodiment, wherein * represents the attachment point to the Ge atom. Said R group has biochemical-responsive ability.

Preparation of the 2D germanane derivatives of the invention

The germanane derivatives of the invention can be prepared by functionalizing 2D-GeH with sulfur-containing ligands.

Thus, in the second aspect, the invention relates to a process for the preparation of a 2D germanane derivative according to the first aspect, wherein the process comprises reacting 2D germanane with a compound of formula (II):

R-H (II) wherein R is as defined in the first aspect, wherein the reaction is carried out in the absence of oxygen or wherein the oxygen concentration is lower than 5% by volume.

In the context of the present invention, the term “absence of oxygen” means that oxygen (O2) is absent from the reaction medium, including any liquid and gas phase wherein the reaction is carried out. The reaction may also be carried out al low oxygen concentrations, preferably at an oxygen concentration lower than 5% by volume. Oxygen may be removed from a gas phase by purging with an inert gas, such as argon, nitrogen and/or helium, preferably argon. Oxygen may be removed from a liquid phase by bubbling the liquid phase with an inert gas, such as argon, nitrogen and/or helium, preferably argon. The oxygen concentration may be determined by a dissolved oxygen probe or sensor.

Preferably, the process of the invention is carried out under an atmosphere selected from the group consisting of argon atmosphere, nitrogen atmosphere and helium atmosphere, more preferably argon atmosphere.

Preferably, the process of the invention is carried out in a polar solvent.

The term “polar solvent” refers to a compound which is liquid at 20 °C and which has a dielectric constant greater than 15 at 20 °C. Examples of polar solvents are alkanols (such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, and t-butanol), acetonitrile, acetone, dimethylformamide, and dimethylsulfoxide.

Preferably, the polar solvent used in the process of the invention is selected from the group consisting of acetonitrile, C1-C4 alkanol, and mixtures thereof; more preferably, acetonitrile, ethanol, and mixtures thereof; still more preferably acetonitrile.

The term “C1-C4 alkanol” refers to a compound consisting of a C1-C4 alkyl chain bonded to a hydroxyl group. Examples of a C1-C4 alkanols are methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, and t-butanol.

When carrying out the process of the invention, the oxygen (O2) that may be present in these solvents is removed as explained above before contacting said solvents with 2D- GeH.

In particular, the concentration of 2D-GeH in the polar solvent is from 0.05 to 5 mg/mL, more preferably from 0.05 to 1.5 mg/mL. In particular, the 2D-GeH is dispersed in the polar solvent.

Preferably, in the process of the invention, the molar ratio of 2D-GeH to the compound of formula (II) is from 10:1 to 4:1 , preferably from 6:1 to 4:1 , more preferably about 5:1. In particular, the process of the invention is carried out by first mixing the 2D-GeH with the polar solvent and then adding the compound of formula (II) to the resulting mixture.

In particular the process of the invention is carried with stirring.

Typically, the process of the reaction of 2D-GeH with the compound of formula (II) takes from 8 to 24 h.

Preferably, the reaction is carried out at from 20 °C to 25 °C.

In particular, after the reaction between 2D-GeH and the compound of formula (II) has taken place, the resulting 2D germanane derivative of the invention may be separated from the reaction media by centrifugation. Preferably, after centrifugation, the 2D germanane derivative of the invention may be washed, in particular using a polar solvent as previously defined, more preferably the washing is performed by three consecutive washing steps.

2D-GeH is commercially available or may be synthesized following the process described in [T. Giousis, et al. Angewandte Chemie, 2021 , 60(1), 360-365],

In an additional aspect, the invention relates to a 2D germanane derivative obtainable by the process of the second aspect.

Uses of the 2D germanane derivatives of the invention

The 2D germanane derivatives of the invention are sensitive to external stimuli, such as redox potential, chiral compounds, chemical compounds having TT bonds, etc.

Thus, the 2D germanane derivatives of the invention can be used as a stimuli responsive materials.

In one aspect, in the 2D germanane derivative R is -S-(CH2)n-ferrocenyl wherein n is from 1 to 20, as previously defined, and the responsive material is used for processing logic information, in particular via redox input - electrochemical output. The processing of logic information an electrochemical system may be used, in particular, wherein the 2D germanane derivative is deposited (e.g., by drop casting, in particular of a dispersion of the 2D germanane derivative in a polar solvent as previously defined, preferably acetonitrile) on an electrode (e.g., a glassy carbon electrode). The electrode may be incorporated in a conventional three-electrode configuration cell containing a working electrode (the electrode comprising the 2D germanane derivative), a counter electrode (e.g., Pt wire electrode) and reference electrode (e.g., Ag/AgCI electrode), filled with a supporting electrolyte (e.g., phosphate buffer solution). The electrochemical measurements may be carried out using a potentiostat/galvanostat.

The electrochemical measurements may be carried out by applying a bias potential before (OFF) and after (ON) the oxidation peak (i.e. before and after, respectively, the potential of the oxidation peak), distinguishing bistable molecular states of the 2D germanane derivative wherein R is -S-(CH2)n-ferrocenyl {Ge-Fc <- [Ge-Fc]+}, through the readout of the real capacitance (C_re) at 0.1 Hz using the electrochemical impedance spectroscopy technique. If the applied bias potential is before the oxidation peak, the electrochemical signal (C_re, output) is low; if the applied bias potential is after the oxidation peak the electrochemical signal is high. The electrochemical signal “low” and “high” are translated into the binary numbers 0 and 1 , respectively, and the logic YES or IDENTIFY operation is straightforward identified: input = 0 leads to output = 0 and input = 1 leads to output = 1. Thus, the reversible electroswitching between two redox forms of a ferrocenyl compound can be interpreted as writing and erasing of information.

In another aspect, in the 2D germanane derivative R is a thiolated cyclodextrin which is covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin, as previously defined, and the responsive material is used for enantiodiscrimination of chiral molecules, in particular via supramolecular input - optical output.

For enantiodiscrimination of chiral molecules, optical measurements are carried out by contacting the 2D germanane derivative with a sample to be analyzed (preferably an aqueous solution) and measuring the fluorescence, typically in a fluorimeter. If the sample contains a chiral molecule, the fluorescence of the system varies with respect to the fluorescence in the absence of a chiral molecule. Said variation also depends on the particular enantiomer present in the sample, i.e., L- and D-amino acids, R- and S- enantiomers, Z- and E- enantiomers, etc, preferably L- and D-amino acids. Thus, the 2D germanane derivative can be used to discriminate between enantiomers, preferably between L- and D-amino acids.

For this purpose, an aqueous dispersion of the 2D germanane derivative may be prepared, for example at a concentration of about 0.025 mg-mL'¹, and contacted with the sample to be analyzed, and the fluorescence is measured. A calibration curve may be prepared by increasing the concentration of enantiomers to be analyzed (e.g., L- and D- amino acids, preferably tryptophan) in the suspension containing the responsive material and monitoring the maximum fluorescence signal. If no chiral analyte (input) is present the fluorescence signal (output) is low; if the chiral analyte is present and above a certain concentration threshold the fluorescence signal is high. The fluorescence signal “low” and “high” are translated into the binary numbers 0 and 1 , respectively, and the logic YES or IDENTITY operation is straightforward identified: input = 0 leads to output = 0 and input = 1 leads to output = 1.

In a further aspect, in the 2D germanane derivative R is -S-A, wherein A is a 6- to 14- membered monocyclic or polycyclic aromatic or heteroaromatic ring system, as previously defined, and the responsive material is used for identifying molecules having a TT bonds (e.g., carbon dots), in particular via chemical input - electrochemical output.

For identifying carbon molecules having a TT bonds, the 2D germanane derivative is integrated in the aforementioned three-electrode electrochemical cell, filled with an electrolyte containing a redox marker (e.g., [Fe(CN)6]³'^/4‘). The electrochemical measurements may also be carried out by applying a bias potential (e.g., at 0.21 V) to the system containing the 2D germanane derivative wherein R is -S-A and the signal (charge transfer resistance, R_ct) is monitored by electrochemical impedance spectroscopy means. Subsequently, an increasing concentration of carbon molecules dissolved/dispersed in water as analyte (e.g., carbon dots) may be added to the electrochemical solution and the charge transfer resistance (R_ct) is measured to create the calibration curve. If no chemical analyte (input) is present the electrochemical signal (Rct, output) is low or even totally absent; if the chemical analyte is present and above a certain concentration threshold the electrochemical signal is high. The electrochemical signal “low (or absent)” and “high” are translated into the binary numbers 0 and 1 , respectively, and the logic YES or IDENTITY operation is straightforward identified: input = 0 leads to output = 0 and input = 1 leads to output = 1. In an additional aspect, in the 2D germanane derivative previously defined, and the responsive material is used for the discrimination of chiral compounds as previously described (e.g., L-amino acid oxidase), in particular via biochemical input - electrochemical output.

For this use, the 2D germanane derivative is integrated in the aforementioned three- electrode electrochemical cell, filled with an electrolyte containing a redox marker (e.g., [Fe(CN)6]³'^/4‘). The electrochemical measurements may also be carried out by applying a bias potential (e.g., at 0.21 V) to the system containing the 2D germanane derivative wherein its L- or D-form and the signal is monitored by electrochemical impedance spectroscopy means. Subsequently, an increasing concentration of chiral compound dissolved in water as analyte may be added to the electrochemical solution and the charge transfer resistance (R_ct) is measured to create the calibration curve. When R is in its L-form, the selectivity is for chiral compounds in its L-form, and vice versa. If no chiral compound (input) is present the electrochemical signal (Rct, output) is high; if the chemical analyte is present and above a certain concentration threshold the electrochemical signal is low. The electrochemical signal “high” and “low” are translated into the binary numbers 0 and 1 , respectively, and the logic YES or IDENTITY operation is straightforward identified: input = 0 leads to output = 0 and input = 1 leads to output = 1 . Contrary, if the chiral analyte does not fit the chirality of R, no signal is obtained, and therefore input = 1 leads to output = 0.

In the context of the present invention, the term “about” refers to the indicated value ±10% of said value, preferably to the indicated value ±5% of said value.

The following examples represent specific embodiments of the present invention. They do not intend to limit in any way the scope of the invention defined in the present description.

EXAMPLES Materials and methods

Reagents germanium hydride, 6-(Ferrocenyl)hexanethiol (> 99 %), 11-

(Ferrocenyl)undecanethiol (> 99 %), thiophenol (> 99 %), L-cysteine (>98%), D-cysteine (>98%) and high-performance liquid chromatography grade acetonitrile solvent were purchased from Sigma-Aldrich. Electrochemical phosphate-buffered saline (PBS) and reagents for preparing the redox marker probe (K3[Fe(CN)e] and K4[Fe(CN)e]) were also acquired from Sigma-Aldrich. Electrochemical aqueous solution was prepared using ultrapure water from a Milli-Q system (Millipore).

X-Ray Diffraction (XRD) measurements were acquired in Bruker AXS D8 advanced diffractometer equipped with a position sensitive detector (PSD) and a curved germanium (111) primary monochromator and the radiation used was Cu-Ka (I % 1.5418 A).

Fourier transform infrared (FTIR) spectra were recorded using a BRUKER spectrophotometer, Alpha II model with single reflection diamond attenuated total reflectance (ATR) module. Measurements were carried out in a range of 400 to 3000 cm^-1.

X-Ray Photoelectron spectroscopy ( PS) measurements were performed with a SPECS PHOIBOS 150 hemispherical analyzer (SPECS GmbH, Berlin, Germany) at room temperature in a base pressure of 5x1 O'¹⁰ mbar using monochromatic Al K alpha radiation (1486.74 eV) with an excitation source operated at 300W. The energy resolution measured by the FWHM of the Ag 3d5/2 peak for a sputtered silver foil was 0.62 eV.

UV-Vis spectra were acquired using a V-730 Jasco spectrophotometer from 800 to 200 nm at 400 nm s'¹ scan rate using a quartz cuvette filled with 0.1 mg mL'¹ of sample in acetonitrile solution.

CD spectra were acquired using a J-815 Jasco spectropolarimeter from 180 to 300 nm at 200 nm s'¹ scan rate using a quartz cuvette filled with 0.1 mg mL'¹ of sample in acetonitrile solution. Fluorescence plots were acquired using a Cary Eclipse Fluorimeter using an excitation wavelength of 354 nm and 338 nm for 2D-GeH and 2D-GeFce, respectively. The emission fluorescence spectra were recorded from 400 to 650 nm in a quartz fluorescence cuvette containing an optimum concentration of sample in acetonitrile solution.

Cyclic Voltammetry (CV) and electrochemical measurements were carried out with a PalmSens4 Potentiostat using PSTrace 5.10.5604 software. The electrochemical experiments were performed using either 0.1 M PBS or 0.1 M KCI containing 10 mM [Fe(CN)6]³'^/4‘ in Mili-Q water at pH = 7.2 as the electrolytes. The three-electrode configuration cell was based on a platinum wire as counter, an Ag/AgCI as reference and a glassy carbon disk electrode drop casting 30 pL of sample (C = 1 mg mL'¹) as working electrodes, respectively. Electrochemical plots were recorded in a range of T 10⁵ to 0.1 Hz using an optimum bias potential.

Synthesis of 2D germanane derivatives

The synthetic conditions for the covalent anchoring of R-SH onto hydrogen-terminated germanane (GeH) is carried out as follows: 1 mg mL'¹ 2D-GeH dispersion in deoxygenated acetonitrile (ACN) is prepared in a round flask under inert conditions. The resulting dark suspension of 2D-GeH is sonicated for 30 min. Next, 2.5 mM R-SH is added to the round flask containing the 2D-GeH and aged for 12 h under stirring conditions in an inner (Ar) atmosphere to induce the new Ge-S chemical bond, resulting in Ge-R. The nature of R-SH and the resulting 2D-GeR materials according to the invention are gathered in the table below.

Results and discussion

Characterization of the germanane derivative

All the germanane derivatives were fully characterized by employing state of the art characterization techniques. Pristine 2D-GeH was also characterized for comparison. What follows discusses the data obtained for 2D-GeFce as a model germanane derivative (Figure 1). At the end of each section the characterization data obtained for the rest of germanane derivatives is briefly discussed.

FTIR

The materials were firstly characterized by Fourier transformed infrared (FTIR) spectroscopy using attenuated total reflection (ATR). Figure 1a shows the FTIR spectra of pristine 2D-GeH and functionalized 2D-GeFce. In the recorded spectra from 3000 to 400 cm^-1, both 2D-GeH and 2D-GeFce samples exhibited the typical Ge-H bands derived from pristine 2D-GeH located at ca. 1990 (vGeH), 570 and 504 cm^-1 (coGeH), as well as the signature of Ge vacancies located between 770 and 830 cm^-1. In addition, the band observed at ca. 987 cm^-1 can be ascribed to the stretching modes of Ge-0 (vGeO), intensity that weakened after material functionalization. Importantly, the characteristic absorption bands of Fce-SH were clearly observed in the spectrum of 2D-GeFce. The fingerprint of the molecular moiety was observed at ca. 2953-2832 cm^-1 — attributed to symmetric (v_sCH) and asymmetric (v_aCH) C-H stretching modes — , 1453 cm^-1 corresponding to the in plane C=C-H asymmetric stretching (v_aCCH) of the aromatic ring, and the C-H stretching vibration from cyclopentadiene (vCp) at 1376 and 1098 cm^-1. Interestingly, the band ascribed to the Ge-H wagging mode (coGeH) of pristine 2D- GeH was significantly blue-shifted from 461 to 473 cm^-1 after molecular functionalization (Figure 1a, inset), suggesting the new Ge-S wagging mode (coGeS) contribution as observed in alternative ligand-terminated 2D-Ge via Ge-C chemical bonds. Then, this shift can be seen as a first indication of the covalent Ge-S bond formation, Remarkably, the absence of the characteristic S-H stretching mode of thiol groups (vSH) reported at ca. 2550-2600 cm^-1 points out the chemical nature of the interaction rather than a physisorption process (see Figure 1 b). Accordingly, FTIR spectroscopy reveals the ferrocene termination of the germanium atoms.

2D-GeFcn, 2D-GePh, 2D-GeCD and L-2D-GeCys were also characterized by FTIR. As shown in Figure 2, FTIR spectrum exhibited the same blue-shift in the band located between 460-470 cm^-1 observed in 2D-GeFce, which must be attributed to the coGeS contribution. In addition, the strong vGeO stretching band of pristine 2D-GeH was notably weaken after the anchoring of the sulfur-containing ligands, suggesting the passivation of the surface. Further, the spectra do not present the typical vSH stretching band centered at 2550 cm^-1, discarding any hypothetic physisorption process.

XPS

The surface chemical composition of the materials was addressed by means of X-ray photoelectron spectroscopy (XPS). The XPS signal due to adventitious carbon located at 284.8 eV was used as a binding energy reference. Figure 1 c shows the high-resolution XPS spectra of pristine 2D-GeH and functionalized 2D-GeFce performed for Ge 3d, S 2p and Fe 2p orbitals. In line with literature [Palacios-Corella et al., Nanoscale, 2022, 14(48), 18167-18174], Ge 3d spectrum of pristine 2D-GeH exhibited three distinct peaks at ca. 32.0 eV, 30.7 eV and 29.2 eV, attributed to Ge-O, Ge-H and Ge-Ge binding energies, respectively. After 2D-GeH functionalization with the sulfur-containing ligand, a new contribution was clearly observed at 27.9 eV, which must be attributed to Ge-S binding energy, confirming the chemical bond formation. In addition, the shift observed in the Ge-Ge binding energy of 2D-GeFce from 29.2 eV to 29.6 eV further corroborates the successful ligand-exchange process. Remarkably, a decrease in the area under the curve of the Ge-0 binding energy was also revealed by the 2D-GeFce sample, suggesting that its functionalization passivates the surface of the Xene, and therefore protects it from spontaneous oxidation, as observed in the FTIR spectra (Figure 1a). Ligand-exchange quantification was calculated by the total area under the curve of the Ge-S contribution, yielding to a 25.2% of Fce-SH. Consequently, a Ge:S ratio of 6:2.5 was obtained, pointing out the efficient ligand-exchange substitution via the process of the present invention. In addition, the high-resolution XPS spectra of S 2p and Fe 2p corroborated the absence of Fce-SH in the pristine 2D-GeH, while a couple of pair of peaks in both spectra were clearly identified in the 2D-GeFce sample. On the one hand, the high-resolution S 2p spectrum displayed a doublet of peaks cantered at 160.3 and 161.6 eV, ascribed to the Ge-S binding energy contributions of the S2p3/2 and S2pi/2 orbitals, respectively. This is also an indication of the covalent nature of the interaction between the Fce-SH molecules and the pristine 2D-GeH. The second doublet was observed at 162.9 eV (S2p3/2) and 164.7 eV (S2pi/2), which must be attributed to the S- C binding energy contribution from the alkane chain of the thiolated moiety. On the other hand, the high-resolution Fe 2p spectrum also revealed the presence of Fe in the 2D- GeFce sample by the two doublets centered at 707.5 and 715.6 eV, as well as at 710.4 and 719.3 eV, corresponding to the 2p3/2 and 2pi/2 orbitals of Fe²⁺ and Fe³⁺, respectively. In order to demonstrate the passivation activity of sulfur-containing molecules on 2D- GeH, the XPS spectra of both 2D-GeH and 2D-GeFc were acquired after 15 days under air exposure. As shown in Figure 1 d, after 15 days the inherent XPS fingerprint of 2D- GeH almost disappeared, leading to a %O as high as 77%. Contrary, the %O for 2D- GeFce was found to be 40%, demonstrating that the devised molecular approach is a powerful strategy to enlarge the time-life of the Xene.

Figure 3 displays the Ge 3d core level spectra of 2D-GeFcn, 2D-GePh and 2D-GeCD which also exhibited the new Ge-S contribution at ~ 28 eV, together with a shift in the Ge-Ge contribution towards higher binding energies (see the Table below for further details). Table. Ge 3d binding energies (in eV) for pristine 2D-GeH, 2D-GeFc6, 2D-GeFcn and

2D-GePh aMeasurements done on a FTO substrate.

This reinforces the assignment made for the Ge-S peak in the 2D-GeFce material (see Figure 1c), corroborating once again the chemical nature of the bonding.

UV-vis spectroscopy

The optical properties of both pristine 2D-GeH and functionalized 2D-GeFce were characterized by UV-vis spectroscopy. Figure 1e shows the UV-vis spectra in a range of 800 to 250 nm using a 1 mg mL'¹ aqueous suspension of sample. The UV-vis spectra of pristine 2D-GeH displayed a maximum absorption band at 602 nm,. Importantly, the 2D- GeFce presented a red-shift in this band to 663 nm owing to the ligand-exchange reaction. This leaded to a notably band-gap shift in the Xene from 1.64 to 1.60 eV, as demonstrated by the Tauc plots presented in Figure 1f. This result supports once again the proper covalent Ge-S bond formation. Moreover, an additional band with a maximum centered at 277 nm was clearly observed in the UV-vis spectra of 2D-GeH, which corresponds to the TT-TT* transitions of the Fc groups.

As shown in Figure 4, the optical features of pristine 2D-GeH were tuned after molecular functionalization, and the determined band gaps were observed to be shifted from 1.64 eV to 1 .60, 1 .58, 1 .61 , 1.62 and 1.61 eV for 2D-GeFc₆, 2D-GeFcn , 2D-GePh, 2D-GeCD and L-2D-GeCys, respectively. Those changes in the band gap can be considered as a clear signal of the successful covalent functionalization. Consequently, the material characterization data obtained for all germanane derivatives are well aligned with the results obtained by 2D-GeFce (proof germanane derivative for discussion). Circular Dichroism

As most of the amino acids, cysteine (Cys) presents an asymmetric carbon responsible for its molecular stereochemistry (L- and D-form). Bearing this in mind, chiroptical properties rapidly became one of the most appealing molecular properties to be studied forL-2D-GeCys. For comparison, D-2D-GeCys was also synthesized. Thus, ciruclar dichroism (CD) experiments were run to characterize the chiroptical properties of 2D- GeH (control), L-2D-GeCys and D-2D-GeCys. Figure 5a shows the CD spectra of isolated L-Cys and D-Cys, presenting a positive and negative CD band at 201 nm, respectively. Then, experiments for 2D germanane derivatives demonstrated a positive CD band for L-2D-GeCys and a negative CD band for D-2D-GeCys, in line with the performance displayed by the isolated chiral amino acid. In addition, the CD band was red-shifted to 183 nm, being an indication of the proper covalent immobilization of the amino acid to the Xene.

As expected, the non-chiral nature of pristine 2D-GeH (control) yielded to no CD absorption band. Consequently, this mirror-image response can be taken as an irrefutable proof of the chiroptical activity of the synthesized 2D germanane derivatives.

Molecularly program (opto)electronic properties

The optoelectronic properties of the 2D-GeFce were modulated by taking advantage of the inherent redox-responsive features of the anchored sulfur-containing ligand. Thus, the implanted molecular redox responsiveness (inputs) has been exploited to monitor a bistable molecular switch with either optical or electrical readouts (outputs), leading to a molecule-programmable Xene.

Modulation of the optical properties of 2D-GeFc₆ (Electrical Input-Optical Output)

Firstly, the implanted molecular responsiveness of the redox-responsive ligand was utilized to tune the intrinsic fluorescence features of the Xene. Fluorescence spectroscopy measurements are shown in Figure 6a. The emission spectra of both pristine 2D-GeH and functionalized 2D-GeFce was centred at A_em = 452 nm, while the excitation wavelength was shifted from A_ex = 354 nm to A_ex = 338 nm after molecular functionalization (Figure 6a, inset), in line with the band-gap change observed in Figure 1g. The highest the electronic band-gap, the lowest the A_ex. In addition, a quenching in the fluorescence intensity as high as 35% was observed for the functionalized 2D-GeFce with respect to the pristine 2D-GeH sample. This result points out the efficiency of the ligand-exchange process and the relevant tunability of the fluorescence properties of 2D-GeH once it is covalently functionalized via Ge-S bond formation. Subsequently, a spectro-electrochemical experiment was performed to study whether the fluorescence features of the 2D-GeFce can be also modulated by manipulating the oxidation state of the iron core of the molecular moiety through a redox-driven bistable molecular switch on the Xene (2D-GeFce <- [2D-GeFce]⁺). As shown in Figure 6b, the fluorescence intensity of 2D-GeFce slightly change up to 3% depending on the redox potential applied to either oxidize (+0.6 V) or reduce (-0.2 V) the Fc moiety. Herein, an increase in the fluorescence intensity was observed after oxidizing the iron core of the ligand, inducing to the reaction: 2D-GeFce — > [2D-GeFce]⁺. Bearing in mind that two possible events can derive from the fluorescence quenching mechanism as a dependence of the redox state of electroactive groups — electron donor or acceptor — , such an intensity increase suggests that the photoinduced electron transfer is more favored when Fc acts as a donor group (2D-GeFce, state OFF) rather than as an acceptor group ([2D-GeFce]⁺, state ON). Importantly, no change in the fluorescence intensity of pristine 2D-GeH (control experiment) was observed after manipulating the redox potential because of the lack of electroactive groups. To further verify this small change in the fluorescence properties of 2D-GeFce, the reversibility of the redox-driven bistable molecular switch was also interrogated. Figure 4c depicts the time vs. fluorescence intensity plot of 2D- GeFce, in which a reversible and stable fluorescent switch with two distinguishable optical states can be clearly observed, demonstrating that the small changes observed in the fluorescence intensity with regarding to the applied bias potential are consistent over time. In addition, while a quick switch in the fluorescence intensity (TON = 0.18 s) was obtained during the oxidation process (bias potential: +0.6 V), the quenching process during the reduction process (bias potential: -0.2 V) was significantly slower (TOFF = 158 s). According to this data, the hole injection mechanism seems to be favored during the oxidation process from 2D-GeFce to [2D-GeFce]⁺, while the electron injection mechanism is hindered during the reduction process from [2D-GeFce]⁺ to 2D-GeFce. As a result, a stable and reversible bistable molecular switch with two distinguishable ON/OFF states was electrically driven and optically readout using a molecule- programmable Xene synthesized via a direct Ge-S bond formation (Figure 6d). Modulation of the electrochemical properties of 2D-GeFc₆ and 2D-GeFcn (Electrical Input-Electrical Output)

Beyond their optical properties, the electrochemical properties of 2D-GeFce were also explored by taking full advantage of the redox responsiveness of the ligand-terminated group. To this end, a fixed amount of 2D-GeFce was drop-casted onto a conventional glassy carbon electrode (GCE) and exposed to a phosphate-buffered saline (PBS) solution at pH 7.2. Figure 7a-b displays the voltametric behavior of pristine 2D-GeH and functionalized 2D-GeFce, respectively, over 50 consecutive cycles. As expected, the electrochemical performance of pristine 2D-GeH just resulted in non-Faradaic currents (Figure 7a), while 2D-GeFce notably displayed a pair of well-defined anodic and cathodic peaks centered at 269 and 224 mV (vs. Ag/AgCI), respectively, which might correspond to a Fc/Fc⁺ redox couple from the iron core (Figure 7b). Importantly, a peak-to-peak separation value (AE) as low as 54 mV was yielded, which must be attributed to the high confinement of the molecular moieties on the semiconductor surface. Remarkably, a lack of fatigue after 50 consecutive cycles was observed as demonstrated by the low current intensity decrease, demonstrating the outstanding robustness of the system as expected by a covalently anchored ligand. In addition, different scan rate vs. current intensity measurements were also conducted for 2D-GeFce in order to corroborate the proper confinement of the molecular moieties (Figure 7c). As shown in Figure 7d, an outstanding linear relationship with the square root of the scan rates for both anodic (r² = 0.999) and cathodic (r² = 0.998) peaks was achieved, indicating a reversible diffusion-controlled process for the Fc/Fc⁺ redox pair.

Afterwards, the suitability of electrochemically monitoring two different electrical states was elucidated by means of electrochemical impedance spectroscopy (EIS), in which the resulting electrical output signals were acquired by means of the real part of the interfacial complex capacitance (C_re) in the frequency range of 0.1 Hz to 100 kHz. This parameter is known to be directly related to the density of charge accumulated at the electrode/electrolyte interface. As shown in the bode plot of Figure 7e, two well- distinguished electrical states were reached before (bias potential: 0.0 V) and after (bias potential: +0.3 V) the redox peaks, leading to a state-to-state gap (AC_re) of 22.0 F cnr² in the low-frequency regime. Importantly, the control experiment carried out using pristine 2D-GeH revealed unaltered C_re changes at the electrode/electrolyte interface, making it possible to ascribe the aforementioned capacitive changes of 2D-GeFce to the different charge states leaded by the ligand-terminated group. Finally, the reversibility of the system was also interrogated by applying successive oxidation/reduction pulses over 12 consecutive cycles (Figure 7f), demonstrating the excellent stability and robustness of two electrical molecular states: [2D-GeFce]⁺ (state ON) and 2D-GeFce (state OFF). All in all, such capacitive changes together with the reversibility and stability of the system upon manipulating the DC bias voltage (ON/OFF) demonstrates the feasibility of the EIS technique to electrically monitor a bistable molecular switch through molecularly programming a Xene with an electroactive ligand-terminal group as Fc. Importantly, this approach is especially appealing owing to the electrical nature of both the input and the output signals, which can be easily integrated with current technologies.

Considering the redox-responsive properties of the GeFcn-SH moiety, the electrochemical performance of the resulting 2D-GeFcn was also evaluated. The cyclic voltammograms of Figure 8a clearly verified the presence of the redox-responsive moiety with oxidation (Fe²⁺/Fe³⁺) and reduction (Fe³⁺/Fe²⁺) peaks located at 382 and 99 mV, respectively. From CV, an estimated F of 1.0T 10'⁹ mol cnr² was obtained for2D-GeFcn, in line with the one yielded by 2D-GeFce (F = 3.89- 10'⁹ mol cm^-2). Finally, EIS measurements were run in order to read out two electrochemical states by means of Cdl, resulting in a ACdi value of 12.5 pF cm^-2 (Figure 8b). In addition, the 2D-GeFcn sample was subjected to several redox cycles by modulating the bias potential, demonstrating an excellent reversibility (Figure 8c). The outstanding molecular switchability can be ascribed to the robustness of the covalent anchoring.

Modulation of the optical properties of 2D-GeCD (Chemical Input-Optical Output)

2D-GeCD was used as a chiral biorecognition agent for the optical enantiodiscrimination of tryptophan (Trp) enantiomers. The fluorescence assay was conducted in a quartz cuvette with acetonitrile solution containing a fixed amount of 2D-GeCD (2 ml, 0.025 mg mL"¹) and a 20 pL aliquot of different concentrations (1 x 10"⁸ to 1 x 10"³ M) of either L-Trp or D-Trp model drugs. After incubating the mixture for 3 min to induce the supramolecular p-CD/Trp complex formation, variations in fluorescence signals were monitored.

Figure 9a-b showed the typical fluorescence emission peak of 2D-GeH (control) at ~ 450 nm before and after increasing concentrations of either L-Trp (Figure 9a) or D-Trp (Figure 9b). Importantly, no changes in the fluorescence signals were observed after increasing concentrations of either L-Trp or D-Trp, indicating the lack of chiral recognition ability of 2D-GeH since no biorecognition moiety (i.e., p-CD) is present in the system. Then, the fluorescent emission spectra of 2D-GeCD was recorded before and after increasing concentrations of either L-Trp (Figure 9c) or D-Trp (Figure 9d). Herein, clear changes in the fluorescence signals were observed, contrary to the pristine 2D-GeH counterpart. Consequently, those changes can be attributed to the supramolecular hostguest interactions between p-CD and Trp enantiomers. In addition, those changes were notably different depending on the enantiomeric form of Trp. Then, the characteristic fluorescence signals were extracted to construct the corresponding calibration curves. As shown in Figure 9e, the sensitivity (slope) of the linear regression curves were clearly different for L-Trp (0.26) and D-Trp (0.13) recognition. Such a large difference in the enantiomeric fluorescence response, which can be explained due to divergent inclusion binding strength of the host p-CD with the different guest enantiomers (stability constant (log K): 2.33 for L-Trp vs. 1.11 for D-Trp) [C. Han, et al. Small, 2008, 4(9), 1344-1350] makes the 2D-GeCD a useful responsive material for the chiral fluorescence sensing of Trp. Notably, the L/D ratio of the slopes was 2:1 , which is consistent with the tabulated log K ratio (2.1 :1).

Modulation of the electrochemical properties of 2D-GePh (Chemical Input- Electrochemical Output)

2D-GePh was utilized for the electrochemical determination of carbon nanoparticles in water by taking advantage of the TT-stacking recognition ability of the anchored aromatic group (Ph). For this goal, 2D-GePh was drop-casted on a GC electrode and used as the working electrode. Electrochemical measurements were run in a conventional three- electrode configuration cell filled with a 0.1 M KCI solution containing 10 mM [Fe(CN)e]³' ^/4‘ as the redox marker.

Figure 10a shows the electrochemical performance of 2D-GePh before and after adding different concentrations of carbon nanoparticles (i.e., carbon dots, CDs). Interestingly, the total impedance of the system (Z) increased with increasing the concentration of CDs. This fact might be ascribed to the semiconducting nature of CDs that favors the overall conductivity of the system. The measurements were carried out per triplicate (n=3), and the resulting calibration curve (Figure 10b) was plotted by representing AZ/Zo, where AZ = Z_x - Zo, being Zo and Z_x the total impedance before and after adding different x concentrations of CDs, respectively.

Claims

1. 2D germanane derivative comprising units of formula (I):

Ge-R (I) wherein R is a sulfur-containing ligand covalently bound through its sulfur atom (or one of its sulfur atoms) to germanium atoms and which is selected from the group consisting of: a) -S-(CH2)n-ferrocenyl wherein n is from 1 to 20, b) a thiolated cyclodextrin which is covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin and which may be optionally substituted by one or more substituents selected from group consisting of which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; -Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-Ci-Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl- NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl, c) -S-A, wherein A is a 6- to 14-membered monocyclic or polycyclic aromatic or heteroaromatic ring system, and which may be optionally substituted by one or more substituents selected from group consisting which may be optionally substituted by one or more substituents selected from group consisting of Ci-Ce alkyl; Ci-Ce alkoxy; -Ci-Ce alkyl-CO(R¹), wherein R¹ is selected from the group consisting of H, -OH, -O-Ci-Ce alkyl, -NH2 and -NH-Ci-Ce alkyl; and -Ci-Ce alkyl- NR²R³, wherein R² and R³ are independently selected form the group consisting of H and -Ci-Ce alkyl, and d) wherein * represents the attachment point to the Ge atom.

2. 2D germanane derivative according to claim 1 , wherein R is -S-(CH2)n-ferrocenyl, wherein n is from 1 to 20, preferably from 5 to 12, more preferably from 6 to 11 , still more preferably 6 or 11.

3. 2D germanane derivative according to claim 1 , wherein R is an unsubstituted thiolated cyclodextrin covalently bonded to the Ge atom by a S atom of the thiolated cyclodextrin.

4. 2D germanane derivative according to claim 1 or 3, wherein R is wherein * represents the attachment point to the Ge atom.

5. 2D germanane derivative according to claim 1 , wherein R is -S-A, wherein A is a 6- to 14-membered monocyclic or polycyclic aromatic ring system, preferably wherein R is - S-phenyl.

6. Process for the preparation of a 2D germanane derivative according to any one of the preceding claims, wherein the process comprises reacting 2D germanane with a compound of formula (II):

R-H (II) wherein R is as defined in any one of the preceding claims, wherein the reaction is carried out in the absence of oxygen or wherein the oxygen concentration is lower than 5% by volume.

7. Process according to claim 6, wherein the process is carried out in a polar solvent, preferably in a solvent selected from the group consisting of acetonitrile and C1-C4 alkanol, more preferably acetonitrile.

8. Process according to claim 6 or 7, wherein the process is carried out under an atmosphere selected from the group consisting of argon atmosphere, nitrogen atmosphere and helium atmosphere, preferably argon atmosphere.

9. Process according to any one of claims 6 to 8, wherein the molar ratio of the 2D germanane to the compound of formula (II) is from 10:1 to 4:1 , preferably from 6: 1 to 4:1 , more preferably about 5:1 .

10. Use of a 2D germanane derivative according to claim 2 for processing logic information.

11 . Use of a 2D germanane derivative according to claim 3 or 4 for enantiodiscrimination of chiral molecules.

12. Use of a 2D germanane derivative according to claim 5 for sensing carbon nanoparticles having a TT bonds.