Electron rich supramolecular polymers as fluorescent sensors for nitroaromatics

Abstract

Three p-electron rich fluorescent supramolecular polymers (1-3) have been synthesized incorporating 2-methyl-3-butyn-2-ol groups in reasonable yield by employing Sonagashira coupling. They were characterized by multinuclear NMR ( 1 H, 13 C), ESI-MS and single crystal X-ray diffraction analyses [1 = 1-(2-methyl-3-butyn-2-ol)pyrene; 2 = 9,10-bis(2-methyl-3-butyn-2-ol)anthracene; 3 = 1,3,6,8-tetrakis(2methyl-3-butyn-2-ol)pyrene]. Single crystal structures of 1-3 indicated that the incorporation of hydroxy (-OH) groups on the peripheral of the fluorophores helps them to self-associate into an infinite supramolecular polymeric network via intermolecular hydrogen bonding interactions between the adjacent discrete fluorophore units. All these compounds showed fluorescence characteristics in chloroform solution due to the extended p-conjugation and were used as selective fluorescent sensors for the detection of electron deficient nitroaromatics. The changes in photophysical properties of fluorophores (1-3) upon complex formation with electron deficient nitroaromatic explosives were studied in chloroform solution by using fluorescence spectroscopy. All these fluorophores showed the largest quenching response with moderate selectivity for nitroaromatics over various other electron deficient/rich aromatic compounds tested (Chart 1). Analysis of the fluorescence titration profile of 9,10-bis(2-methyl-3butyn-2-ol)anthracene fluorophore (2) with 1,3,5-trinitrotoluene/2,4-dinitrotoluene provided evidence that this particular fluorophore detects nitroaromatics in the nanomolar range [2.0 ppb for TNT, 13.7 ppb for DNT]. Moreover, sharp visual color change was observed upon mixing nitroaromatic (DNT) with fluorophores (1-3) both in solution as well as in solid phase. Furthermore, the vapor-phase sensing study of thin film of fluorophores (1-3) showed efficient quenching responses for DNT and this sensing process is reproducible. Selective fluorescence quenching response including a sharp visual color change for nitroaromatics make these tested fluorophores (1-3) as potential sensors for nitroaromatic compounds with a detection limit of ppb level.

ICT based molecular recognition of 2,5-dinitrophenol in methanol

“…Wavelength ratiometric sensors for explosive are really scanty. Though analyte can modulate fluorescence emission in a number of ways, either by excited state or by ground state phenomena or even by a combination of the two, yet most chemosensors of NAC reported to date operate by the modulation of one photophysical process, namely the photoinduced electron transfer (PET) [1][2][3][4][5][6][7][8][9][10][11][12][13] and not the internal charge transfer (ICT) The only report of ICT is by Xu et al [14] for picric acid available as a ratiometric sensor to date to the best of our knowledge. Typically the Schiff base fluorophore contains both electron-donating and electron-accepting groups in its backbone.…”

“…But in almost all cases only intensity based sensors are reported [1][2][3][4][5][6][7][8][9][10][11][12][13] till date. Wavelength ratiometric sensors for explosive are really scanty.…”

“…A number of satisfactory chemosensors for NACs, with particular importance to TNT have been reported [1][2][3][4][5][6][7][8][9][10][11][12][13][14] to date. Mostly in all cases whether it is polymeric matrix, polymer imprinted fluorophore or electron rich discrete fluorophore, the fluorescence interaction exhibited quenching.…”

Resonance light scattering detection of uranium based on its reaction with a Schiff base containing tetradentate ligand and phosphate groups to form supramolecular polymer

“…They can be applied in many fields by utilizing their properties. An important application field of SPs is utilizing their spectroscopic properties for the determination of target analytes [22][23][24][25]. The self-assembly of monomers to form SPs is a procedure of particle volume enlargement and can cause an enhanced RLS signal.…”

Fluoroscence Quenching Studies of Bsa Doped Polyaniline

“…Hence Polyaniline and its similarities find use in the field of sensors, actuators, super-capacitors, electromagnetic-shielding, corrosion protection, as well as electronic, electroluminescence and electro chromic devices [5][6][7][8][9]. Because of this prolonged conjugation inter-molecular hydrogen bonds are formed between the NH2 and NH-R group of the head-to-head chain and π stacking occurs.…”