Sensing properties of light-emitting single walled carbon nanotubes prepared via click chemistry of ylides bound to the nanotube surface †

Pyridinium ylide functionalized single-walled carbon nanotubes (SWCNTs) generated from simple quaternary pyridinium salts covalently bound to the SWCNT surface undergo a 1, 3 dipolar cycloaddition with dimethyl acetylenedicarboxylate in a ‘ click ’ chemistry type fashion to yield indolizine modi ﬁ ed light-emitting SWCNTs. Conversion of quaternary pyridinium salts into indolizines on the SWCNT surface was con ﬁ rmed by XPS, ﬂ uorescence spectroscopy and optical microscopy. The resulting modi ﬁ ed SWCNTs were found to emit blue light when excited at 330 nm. Fluorescence quenching experiments performed via nitroaromatic compounds displayed that the ﬂ uorescence of the modi ﬁ ed SWCNTs was quenched by nitrophenol derivatives in both solution-state and solid-state, probably due to strong H-bonding interaction between host and guest molecules. The functionalized SWCNTs were further characterized using TGA-MS, FTIR and UV-vis-NIR spectroscopy.


Introduction
Chemical sensing has gained much attention due to increasing demand for monitoring environmental pollution, detecting warfare and security threats, developing diagnostics for medical care and providing efficient and sensitive tools for quality control in industrial applications. 1 Due to their interesting chemical and physical properties carbon nanotubes (CNTs) have been used for chemical sensor applications, each based on alterations of a particular feature of a functional material including conductivity for chemiresistors 2,3 and back gate eld effect transistors [3][4][5][6] and the intensity of scattered light resulting from the adsorption of chemical species for photo chemical or optical sensors. [7][8][9][10][11] Substantial effort, therefore, has been devoted in fabricating SWCNT based sensors and the surface functionalization of CNTs in order for utilizing them for sensing. Following the discovery of bright uorescence in the 800 to 1600 nm wavelength range of the near infrared from onedimensional direct band gap semiconducting tubes, 12 a SWCNT based near-infrared optical sensor for glucose detection was fabricated by assembling a monolayer of the enzyme on nanotube surface followed by ferricyanide functionalisation. 13 Pyrene-modied b-cyclodextrin-decorated SWCNT eld-effect transistor device as a photosensor was used to probe a uorescent adamantyl-modied Ru complex through a chargetransfer mechanism from pyrenecyclodextrin-SWCNT hybrids to adamantyl-modied Ru complex. 14 A chemiresistive sensor based on SWCNT and hexauoroisopropanol functionalised polythiophene for the detection of chemical warfare agents including sarin gas and dimethyl methylphosphonate has been shown by a simple spin-casting technique, 3 where the sensory response was investigated measuring the conductance of the SWCNT deposition. Fabrication of uorescent chemosensors were achieved by covalently quinoline modied CNTs for Cu 2+ and Zn 2+ ions 15,16 and CNTs bearing adsorbed DNA with 6-car-boxyuorescein groups for Hg 2+ . 17 Introducing surface groups also enhanced the processability of CNTs, particularly SWCNTs, in both aqueous and nonaqueous solvents by interrupting the strong van der Waals forces causing aggregation or bundling of the material. Covalent strategies to functionalize SWCNTs have included carbene, 18 radical, 19,20 cycloaddition, 21-24 organolithium addition 25,26 and oxidation 27,28 reactions and been recently reviewed. 29 Among radical reactions aryl diazonium salts addition 19,[30][31][32][33][34] has widely been studied using diazonium salts directly 30 or generating them in situ by oxidation of the corresponding aniline with inorganic 31 or organic 32 oxidants. In our research group, it was shown that pyridine diazonium salts underwent a radical addition reaction to SWCNTs to yield pyridine-functionalized SWCNTs which were able to act as cross-linkers and hydrogen bond to poly(acrylic acid) to form SWCNT hydrogels. 35 'Click' chemistry, dened as a modular reaction bringing together two simple units to generate a more complex substance, is gaining momentum in materials science. 21,36 For CNTs 'click' chemistry is predominately based around the Huisgen cycloaddition of azides to alkynes and has been used to attach polystyrene, 37 b-cyclodextrin 38 and phthalocyanines 39 to the surface of nanotubes. Although other simple 1, 3-dipolar cycloaddition reactions also t the criteria of 'click' chemistry such as the reaction described here.
Herein diazonium salt addition and 1, 3-dipolar cycloaddition reactions were utilized in a modular type fashion to introduce light emitting groups to the surface of SWCNTs in a 'click' chemistry type fashion at low temperatures. Fluorescent SWCNTs were tested as sensor to probe nitroaromatic compounds in both solution-state and solid-state.

Experimental
Material preparation 1. SWCNTs. Puried SWCNTs, produced by the HiPco method, were purchased from Unidym, USA, and further puri-ed by heating in air at 400 C and soaking in 6 M HCl overnight. The puried SWCNTs were isolated by ltration over a polycarbonate membrane (0.2 mm, Whatman), and washed with copious amounts of high-purity water until pH neutral. The puried SWCNTs were annealed under vacuum (10 À2 mbar) at 900 C to remove residual oxygen containing functional groups and any adsorbed gases or solvents.
2. SWCNT-pyridine (SWCNT-Py). SWCNT-Py was prepared following the literature procedure. 35 In brief, pyridine diazonium salt generated was reacted with SWCNTs at 0 C in N,N-dimethylformamide (DMF). The modied SWCNTs were ltered through a nylon membrane (0.2 mm, Whatman), re-dispersed in 2 M HCl (100 mL), ltered and washed with copious amount of water until pH neutral. The resulting solid material was dispersed in 2 M NaOH (100 mL) and stirred overnight to ensure deprotonation of the pyridinium salt to pyridine. The functionalized SWCNTs were then isolated by ltration through a nylon membrane (0.2 mm, Whatman) and washed with water until pH neutral and re-dispersed and ltered using THF (2 Â 30 mL), acetone (2 Â 30 mL) and ethanol (2 Â 30 mL), respectively and dried overnight at 80 C to afford SWCNT-Py.

Results and discussion
Herein, an elegant synthetic protocol to introduce lightemitting groups to the surface of SWCNTs via diazonium salt addition followed by 'click' chemistry is demonstrated using the reactivity of pyridine lone pair. The pyridinium ylide, rather than reacting with the CNT surface directly, is covalently bonded to the nanotube which then undergoes 1, 3-dipolar cycloaddition with dimethyl acetylenedicarboxylate (DMAD) to yield uorescent indolizines, Scheme 1. In contrast to previously reported method, 21,23 combined diazonium salt-click chemistry approach described here offers high yielding indolizine formations at low temperatures, more control on reaction conditions, possible choice of dipoles/dipolarophiles with desired side groups (e.g. cyclodextrins, 40 activated alkynes or alkenes at low temperatures 41 ) and the characterization of reaction intermediates. It may further provide a route to generate various quaternary pyridinium salts bearing alkyl, aryl or polymers (e.g. poly(ethylene glycol)) that is likely to enhance the solubility and processability of SWCNT material. However, multistep surface functionalization of SWCNTs resulted in low yields of isolated products that had noteworthy effect on the characterization of modied SWCNTs by concentration/thickness dependent techniques including FTIR and XPS.
In agreement with the previous literature ndings, 35 electronic spectrum of SWCNT-Py in DMF showed suppressed van Hove singularities, indicative of covalent surface modication (see ESI Fig. S1 †). A stable dispersion of SWCNT-Py had a concentration of $160 mg mL À1 , calculated using the Beer's law and an extinction coefficient of 30 mL mg À1 cm À1 and absorption values at l ¼ 700 nm, 42 which decreased dramatically to 0.2 mg mL À1 upon the addition of ethyl-2-bromoacetate to form the Kröhnke salt (1a) which increased to 40 mg mL À1 following 'click' reaction to form the indolizine functionalized SWCNTs (1b). Table 1 shows the solubility of the stable dispersion of Kröhnke salt modied SWCNTs (1a, 2a and 3a), indolizine functionalized SWCNTs (1b, 2b and 3b) and pyridine functionalized SWCNTs (SWCNT-Py) in both DMF and ethanol (EtOH). Solubility of SWCNT-Py in both DMF and EtOH decreased aer the formation of 1a, 2a and 3a. However, solubility in DMF increased aer the cycloaddition reaction to yield indolizines while the solubility of in EtOH decreased, probably due to solute/solvent interactions.
The ATR-FTIR spectra of 1b-3b, Fig. 1, displayed the presence of the ester groups attached to the indolizine ring as a broad band (n CO ) centred around 1730 cm À1 (along with multiple bands between 1600-1300 cm À1 , presumably from the formation of the indolizine). 43 The bands ca. 2850-2990 cm À1 in the spectrum of 3b that are up-shied compared with 1b were attributed to the aromatic C-H stretching, and the band at 1270 cm À1 indicated the -NO 2 symmetric stretching (n NO 1270 cm À1 ), conrming the presence of nitro groups. 44,45 The FTIR spectrum of 2b was noisy compared to others, probably due to the thickness of the lm prepared.
In order to conrm the pyridinium salt formation and their conversion into indolizine via 'click' reaction, quaternary pyridinium salt modied (1a and 3a) and indolizine modied (1b and 3b) SWCNTs were further analyzed by X-ray photoelectron spectroscopy (XPS). Fig. 4 shows deconvoluted N 1s XPS spectra of (1a, 1b, 3a and 3b). The deconvoluted N 1s XPS spectrum of 1a showed three peaks that can be probably attributed to the quaternary nitrogen (N + ) at ca. 402.3 eV, 23,46 pyridinic nitrogen at 398.9 eV (ref. 21, 23 and 35) and pyridine radical cation (N + c) at 400.2 eV. 47,48 Aer the 'click' reaction of 1a with DMAD, the deconvoluted N 1s XPS spectrum of 1b displayed two unchanged peaks positioned at ca. 399.9 and 398.9 eV and a new peak generated at 401.4 eV that probably correspond to indolizine ring nitrogen (-N<). 49 The deconvoluted N 1s XPS spectrum of 3a showed signature of nitro group (-NO 2 ), 23 pyridine diazo (-N]N), 50 quaternary nitrogen (N + ) 23 and pyridine radical cation (N + c) 47,48 at ca. 406.2, 403.8, 402.4 and 400.1, respectively. Similar to 1b, aer the 'click' reaction, the deconvoluted N 1s XPS spectrum of 3b displayed a new peak formation positioned at ca. 401.5 eV as an indication of indolizine formation. N 1s XPS spectra of both 1b and 3b showed no peak related to quaternary pyridinium nitrogen (N + ), conrming that  pyridinium salts were successfully converted into pyridinium ylides, which subsequently reacted with DMAD to yield indolizines. Compared to the atomic per cent (at%) nitrogen (2.90%) found in SWCNT-Py, XPS elemental analysis results of 1b, 2b and 3b veried the presence of 2.22 AE 0.33, 1.60 AE 0.22 and 2.16 AE 0.56 atomic per cent (at%) nitrogen, respectively, suggesting nitrogen free new group addition (e.g. DMAD, PEG, benzene ring etc.) to SWCNT surface.

Fluorescence properties of indolizine modied light-emitting SWCNTs
The presence of uorescent groups, so-called indolizine heterocycles, on nanotube surface was also conrmed by uorescence spectroscopy where the studies showed that the indolizine functionalized SWCNTs (1b and 2b) emitted light upon excitation (Fig. 5). Excitation of 1b and 2b at 330 nm resulted in a blue emission at ca. 404 nm. To compare, free indolizine (FI), 3-ethyl 1,2-dimethyl indolizine-1,2,3-tricarboxylate was synthesised following the literature 45 via the addition of ethyl-2-bromoacetate to pyridine to afford N-(ethoxycarbonylmethyl)-pyridinium bromide which undergoes the 1, 3-dipolar cycloaddition reaction with DMAD in the presence of a base (NEt 3 ) (see Experimental section and ESI Scheme S1 †). Compared to 1b and 2b, excitation of FI at 330 nm resulted in a blue shied emission at ca. 382 nm, suggesting an electron transfer between electron rich indolizine and SWCNT upon the covalent attachment of indolizines to SWCNT surface. Control experiments mechanically mixing the FI with puried SWCNTs followed by washing with THF, acetone and ethanol showed no sign of uorescence indicating that the uorescence is not due to the physically adsorbed uorescent indolizines (Fig. 5). In contrast to 1b and 2b, excitation of 3b at 330 nm showed no sign of uorescence (Fig. 5). It was no surprise since the structures like 3b bearing strong electron withdrawing groups (e.g. -NO 2 groups) are likely to be quenched. 51 Nitro groups of 3b were reduced to amine (-NH 2 ) moieties using Sn/HCl 52 to synthesize amino group modied SWCNTs (3c) (Scheme 1). As expected, excitation of 3c at 330 nm emitted at 430 nm following the conversion (Fig. 5). XPS was used to conrm the reduction of nitro (NO 2 ) groups into amines (NH 2 ). N 1s XPS spectrum of 3c showed three components positioned at 406.4, 401.0 and 399.2 eV, corresponding to nitro groups (-NO 2 ), 23 the indolizine ring nitrogen (-N<) 49 and pyridinic nitrogen, 35 respectively (see ESI Fig. S2 †). Decrease in the ratio of the relative peak intensity between the peak positioned at ca. 406.4 eV (nitro group nitrogen) and $400 eV (pyridinic nitrogen) (I 406 /I 400 ¼ 0.57) in N 1s XPS spectrum of 3b (see Fig. 4) suggested that nitro groups were almost reduced when compared to the N 1s XPS spectrum of 3c with I 406 /I 400 ratio of 0.08 (see ESI Fig. S2 †).
Furthermore, the presence of a signicant tail in the green region ($500 nm) of the emission spectra allowed us to optically image modied SWCNT materials (1b, 2b and 3c). Fig. 6 shows the white light optical image (le) and the epi-uorescence image (right) of indolizine modied SWCNTs (1b, 2b and 3c). Fluorescence images were recorded using excitation light transmitted through a 420 to 480 nm excitation lter and uorescence observed aer passage through a 500 nm emission lter (Olympus CX-DMB-2 cube). The green spots can be clearly seen on the epi-uorescence image (right) of modied SWCNTs (1b, 2b and 3c) as an indication of covalently attached light emiting indolizine groups on SWCNT surface, suggesting that the quantum efficiency of the emitted light is probably sufficient for practical applications (e.g. uorescent imaging) (Fig. 6). However, we were unable to calculate the absolute quantum efficiencies of the indolizine modied SWCNTs (1b, 2b and 3c) due to the strong scattering and absorption of the SWCNTs. As comparison it was possible to determine the quantum yield of the FI heterocycle. The uorescence quantum yield (F f ) of FI was determined from the corrected uorescence spectra as 0.055, using anthracene dissolved in ethanol as a standard (F st f ¼ 0.27 at 25 C). 51

Solution state photochemical sensing properties of indolizine modied light-emitting SWCNTs
With the given uorescent properties it is expected that indolizine modied SWCNTs may be used as molecular sensing probes. Indolizine modied light-emitting SWCNTs (1b) was used as a host molecule to probe potentially dangerous nitroaromatics photochemically in solution-state. Phenol (P), 2nitrophenol (2NP), 3-nitrophenol (3NP), 4-nitrophenol (4NP), 4nitrotoluene (4NT) and 2,4-dinitrotoluene (2_4NT) were selected as guest molecules. A literature method has been followed to evaluate the solution phase photochemical sensing properties of 1b. 53 Shortly, a stock solution of 1b ($1.50 mg mL À1 , $1.25 Â 10 À4 mol L À1 ) and the guest molecules (1 Â 10 À4 mol L À1 ) were prepared in acetonitrile (CH 3 CN) for uorescence spectral analysis. Each time a 3 mL solution of 1b was lled in a quartz cell of 1 cm optical path length, and stock solutions of guest molecules were added into quartz cell portion wise (2, 2, 2, 2, 2, 5, 5, 5, 25, 25, 25, 100 mL) and mixed for 10 seconds. Measurements were performed immediately aer mixing. An excitation wavelength of 330 nm and a temperature of 25 C were employed in all experiments. Emission spectra of the guest molecules in CH 3 CN showed no emission upon excitation at 330 nm (see ESI Fig. S3 †). Fluorescence response of 1b (3 mL, $1.25 Â 10 À4 mol L À1 ) to the guest molecules was initially tested by adding known amount of aromatic compound (P, 2NP, 3NP, 4NP, 4NT and 2_4NT) (200 mL, 1 Â 10 À4 mol L À1 ). Aromatic nitrophenol derivatives (2NP, 3NP and 4NP) caused a signicant decrease in the uorescence intensity of 1b compared to P and nitrotoluene derivatives (4NT and 2_4NT) (see ESI Fig. S4 †). Fluorescence spectra of 1b aer the guest molecule addition suggested that uorescent quenching efficiency (FQE) of 4NP was the highest among the guest molecules although it was not the least electron decient one. FQE was observed in the order of 4NP > 2NP > 3NP > P > 4NT > 2,4NT (see ESI Fig. S4 †). As expected, portion wise addition of 4NP (2, 2, 2, 2, 2, 5, 5, 5, 25, 25, 25, 100 mL) showed a signicant, regular decrease trend in uorescence intensity of 1b, suggesting an intermolecular interaction between 1b and 4NP (Fig. 7). Detection limit of photochemical sensing was estimated as 6.66 Â 10 À8 mol L À1 , considering the nal concentration of 4NP aer 2 mL addition. However, the detection limit may be lower than the estimated value since some of 4NP molecules are likely to be physically adsorbed by SWCNT surface and reduce the concentration of free 4NP in analysed solution. Adsorption of 4NPs was previously shown where a SWCNT based device was developed assembling nanotubes to electrodes using AC dielectrophoresis technique which allows the real-time detection of adsorbed nitrophenols in aqueous solution. 54 The Stern-Volmer relationship allows us to investigate the kinetics of a photophysical intermolecular deactivation process and, luminescence in solution obeys the linear Stern-Volmer relationship, 55 , where F 0 denotes the initial intensity of the uorescent species without quencher, F represents the  nal intensity of the uorescent species with quencher, k q is the quencher rate coefficient, s 0 is the uorescence lifetime of the uorescent species without a quencher and [Q] is the concentration of the quencher. The Stern-Volmer plot constructed by the emission data obtained from the addition of 4NP to 1b displayed a linear prole, probably indicating a single set of uorophores, all equally accessible to the quencher (Fig. 8). 56 Similarly, uorescent quenching of 1b using other guest molecules (P, 2NP, 3NP, 4NT and 2,4NT) was also studied. Addition of 2NP and 3NP displayed similar decreasing trend in uorescent intensity of 1b while the change in the uorescent intensity upon the addition of P, 4NT and 2,4NT is not signicant (see ESI Fig. S5-S9 †).
In order to further explore the intermolecular interactions between 1b and 4NP, photochemical sensing properties of free indolizine (FI) structure, as a model, were also studied by uorescence spectroscopy, FTIR and NMR. In agreement with 1b, uorescence spectral analysis of FI (3 mL, 2.09 Â 10 À7 M) in the presence of P, 2NP, 3NP, 4NP, 4NT and 2,4NT (200 mL, 1 Â 10 À4 mol L À1 ) showed similar decreasing trend in the uorescent intensity of FI, displaying a FQE order of 4NP > 2NP > 3NP > P > 4NT > 2,4NT (see ESI Fig. S4 †). Given the highest ability of 4NP to quench the uorescence of FI this process was further investigated performing binding experiments. Similar to 1b, FI was titrated with 4NP. As expected, similar trend in the uorescence intensity of FI was observed aer the addition of 4NP, conrming that the change in intensity is purely due to the intermolecular interactions between host and guest molecules (see ESI Fig. S10 †). It further conrmed that SWCNTs were functionalized by light-emitting indolizine groups that are able to sense particularly nitrophenol derivatives.
To investigate the nature of intermolecular interactions between FI and 4NP, spectroscopic analysis of the FI, 4NP and possible FI:4NP complex were carried out by NMR and FTIR. Equimolar amounts of vacuum-dried FI (10.64 mg, 3.28 Â 10 À2 mmol) and 4NP (4.5 mg, 3.28 Â 10 À2 mmol) were dissolved in 1 mL of anhydrous freeze-dried CDCl 3 for NMR spectroscopy analysis. Dry experimental conditions ensured that there was no possible proton exchange with water. Fig. S11 † shows the 1 H NMR spectra of FI, 4NP and the mixture (FI:4NP). The 1 H NMR spectrum of FI:4NP showed that the hydroxyl proton of 4NP (H a ) at 5.74 ppm disappeared upon mixing with FI, suggesting a strong intermolecular interaction that can probably be attributed to H-bonding interaction/proton transfer between hydroxyl proton of 4NP and FI. 43,57,58 However, no signicant signal shi was observed for the aromatic protons H c , H e , H j and H k , probably indicating weak or no p-p interactions between FI and 4NP. Complementary FTIR spectroscopy further conrmed the possible H-bonding interaction between FI and 4NP. FTIR spectra of compounds were recorded by dropping the stock solutions of the compounds (FI and 4NP) and the mixture (FI:4NP) on vacuum dried KBr disk (see ESI Fig. S12 †). FTIR spectrum of FI displayed three n C]O stretching vibrations at 1740, 1710 and 1695 cm À1 due to the presence of ethoxy and methoxy ester carbonyl groups. In contrast, FTIR spectrum of the mixture (FI:4NP) showed a strong broad n C]O stretching at 1700 cm À1 . Signicant change in shape and position of the n C]O stretching bands of FI aer the addition of 4NP revealed a strong intermolecular interaction, probably H-bonding between ester carbonyl of FI and hydroxyl proton of 4NP. 43,53,59 Solid state photochemical sensing properties of indolizine modied light-emitting SWCNTs Due to their exceptional physical and chemical properties, SWCNTs can be used as solid support materials for various applications including sensors. 60,61 Previously, it was shown that calculated photoluminescence quantum yield (PLQY) of uorescent systems could be used as a tool to probe the sensing properties of uorescent materials. 62 Similar to previous work, solid state photophysical properties of 1b and 3c were studied by exposing them to saturated 4NP vapour using a commercial spectrometer coupled with an integrating sphere. 62 The vapour pressure of 4NP at room temperature was previously reported as 1.9 Â 10 À5 mm Hg that corresponds to a vapour concentration of 19 ppb. 63 Fluorimetry experiments were performed on a quartz substrate coated with light-emitting SWCNTs. An excitation wavelength of 340 nm was selected for all measurements. PLQY of 1b and 3c was determined using the formalism outlined by de Mello where F PL is PLQY, E i (l) and E 0 (l) are, respectively, the integrated luminescence as a result of direct excitation of SWCNTs and secondary excitation, L i (l) and L 0 (l) are the integrated excitation when SWCNTs are directly excited and the excitation light rst hits the sphere wall, respectively and, L e (l) is the integrated excitation prole for an empty sphere. 64 Using the equation, PLQY of 1b and 3c was calculated as 0.9 and 0.3%, respectively (Fig. 8). As expected the PLQY of the modied SWCNTs was less than the free indolizines (FI and FI NH 2 (ref. 43)) with calculated PLQY of 5.5 and 3.5%, respectively, probably due to the charge transfer from the electron rich indolizine system to the electron poor SWCNTs. These ndings were in agreement with the blue-shi in emission spectra of 1b and 3c compared to pure spectra of FI and FI NH 2 . 43 Similar decreasing trend in PLQY due to interaction between surface groups and SWCNT walls was previously reported in which the emission quantum yield of 2,4,6-triphenylpyrylium functionalized SWCNTs (F ¼ 1%) was lower than 2,4,6-triphenylpyrylium alone (F ¼ 33%). 65 The change in absorption (A in the equation) of the corresponding indolizine modied SWCNTs (1b and 3c) can be used as a measure of the photochemical response to 4NP vapour since the absorption of uorescent material is expected to change upon the adsorption of 4NP to modied SWCNT surface. 62 Before exposing to 4NP vapour, the absorption values of 1b and 3c were determined as 0.62 and 0.79, respectively. The values decreased to 0.57 and 0.78 aer exposing uorescent SWCNTs to 4NP vapour for 10 seconds (Fig. 8). Furthermore, the calculated PLQY of 1b and 3c slightly increased to 1.1 and 0.4%, respectively following 4NP exposure (Fig. 8). The change in absorption (A in the equation) of the corresponding indolizine modied SWCNTs (1b and 3c) together with the change in the calculated PLQYs revealed that nitrophenol derivatives can be photo chemically probed by indolizine modied light-emitting SWCNTs in solid-state at room temperature on a solid substrate.

Conclusions
A low temperature, highly controllable and efficient synthetic protocol to prepare indolizine modied light-emitting SWCNTs from pyridinium ylides generated on SWCNT surface was presented. Reactivity of the pyridine nitrogen lone pairs allowed the preparation of several quaternary pyridinium salt modied SWCNTs, which were subsequently used to synthesize pyridinium ylide functionalized SWCNTs and indolizine functionalized SWCNTs via 'click' chemistry. Shortly, the current study proposed a new perspective for the synthesis of carbon nanotube supported uorescent molecules and their use in sensing of potentially dangerous nitrophenol derivatives. The indolizine modied light-emitting SWCNTs (1b, 2b and 3c) were shown to emit blue light (400-450 nm) upon excitation at ca. 330 nm. Fluorescent quenching of 1b demonstrated that trace analysis of nitrophenol derivatives could be performed by indolizine modied light-emitting SWCNTs in both solutionstate and solid-state. The orescent quenching was discussed work equally as well with 3c. 1 H NMR and FTIR analysis of free indolizine (FI) structure suggested that the uorescence of the modied materials quenched via probably an electron transfer from electron-rich indolizine to electron-decient nitrophenolics through H-bonding interaction between ester carbonyls of indolizine and hydroxyls of nitrophenol. Optical microscopy images together with solid-state photophysical data revealed that indolizine modied uorescent SWCNTs may potentially be used for imaging in cell transfection and drug delivery due to their high enough quantum efficiencies. Described methodology can be further expanded to introduce various molecules including cyclodextrins and cucurbituril with uorescent indolizine tags on SWCNT surface that may be used for protein sensing and crystallisation. Furthermore the preparation of uorescent hierarchical networks of carbon nanomaterials (e.g. carbon nanotubes and graphene) are anticipated via the reaction of bisdipolarophiles (e.g. bisacetylenes) with pyridinium ylides generated on carbon materials. The principles outlined here are expected to be applicable to other low dimensional materials including graphene and related inorganic layered materials.