Fluorescent Polystyrene Microbeads as Invisible Security Ink and Optical Vapor Sensor for 4-Nitrotoluene

Abstract

Color-tunable solid-state emitting polystyrene (PS) microbeads were developed by dispersion polymerization, which showed excellent fluorescent security ink characteristics along with sensitive detection of vapors of nitro aromatics like 4-nitro toluene (4-NT). The fluorophores pyrene and perylenebisimide were incorporated into the PS backbone as acrylate monomer and acrylate cross-linker, respectively. Solid state quantum yields of 94 and 20% were observed for the pyrene and perylenebisimide, respectively, in the PS/Py and PS/PBI polymers. The morphology and solid state fluorescence was measured by SEM, fluorescence microscopy, and absorbance and fluorescence spectroscopy techniques. The ethanol dispersion of the polymer could be used directly as a fluorescent security "invisible" ink, which became visible only under ultraviolet light. The color of the ink could be tuned depending on the amounts of the pyrene and perylenebisimide incorporated with blue and orange-green for pyrene alone or perylenebisimide alone beads respectively and various shades in between including pure white for beads incorporating both the fluorophores. More than 80% quenching of pyrene emission was observed upon exposure of the polymer in the form of powder or as spin-coated films to the vapors of 4-NT while the emission of perylenebisimide was unaffected. The limit of detection was estimated at 10(-5) moles (2.7 ppm) of 4-NT vapors. The ease of synthesis of the material along with its invisible ink characteristics and nitro aromatic vapor detection opens up new opportunities for exploring the application of these PS-based materials as optical sensors and fluorescent ink for security purposes.

Near infrared absorption/emission perylenebisimide fluorophores with geometry relaxation-induced large Stokes shift

“…Recently, perylenebisimide (PBI) and its derivatives have been widely applied to the areas of uorescence probe and intracellular uorescence imaging image, [1][2][3][4][5] organic photovoltaic devices, [6][7][8][9][10][11][12] charge transporting materials, [13][14][15][16][17][18] luminescent materials [19][20][21][22][23][24] and triplet photosensitizers [25][26][27][28][29][30][31][32] due to its excellent luminous performance, photo-stability and electronic transmission capacity. Traditional PBI dyes always show the strong absorption in visible region and with small Stokes shi (generally less than 60 nm).…”

Photophysical Properties of Phthalimide and Pyromellitic Diimide Tethered Imidazolium Nitrophenolate Salts

“…In general, nitro‐phenolic compounds are pollutant and high energy materials . There are good numbers of reports on their detection in solution or as vapor . Majority of studies are based on the emission quenching and relative sensitivity of the quenching.…”

Probing cavity versus surface preference of fluorescent template molecules in molecularly imprinted polystyrene microspheres

“…Among the sensitive methods of characterization, emission techniques like fluorescence, phosphorescence, and chemiluminescence are interesting areas of research that is being pursued world wide . Fluorescent probes have the ability to exhibit different photophysical characteristics under different environments, which can be effectively made use of in rebinding studies in MIPs .…”

“…27 Among the sensitive methods of characterization, emission techniques like fluorescence, phosphorescence, and chemiluminescence are interesting areas of research that is being pursued world wide. [28][29][30] Fluorescent probes have the ability to exhibit different photophysical characteristics under different environments, which can be effectively made use of in rebinding studies in MIPs. 31 MIPs incorporated with fluorescent dyes in the backbone has been reported for application Additional Supporting Information may be found in the online version of this article.…”