Synthesis, Optical Spectroscopy, and Laser and Biomedical Imaging Application Potential of 2,4,6-Triphenylpyrylium Tetrachloroferrate and Its Derivatives

Abstract

Synthesis, optical spectroscopic properties, two-photon (TP) absorption-induced fluorescence, and laser and bioimaging application potentials of 2,4,6-triphenylpyrylium tetrachloroferrate (1),4-(4-methoxyphenyl)-2,6-diphenylpyrylium tetrachloroferrate (2), 2,6-bis(4-methoxyphenyl)-4-phenylpyrylium tetrachloroferrate (3), and 2,4,6-tris(4-methoxyphenyl)pyrylium tetrachloroferrate (4) are presented. The synthesis involves the conversion of pyrylium tosylates to pyrylium chlorides, followed by transformation into 1−4 on heating to reflux with FeCl 3 in acetonitrile. They are characterized using 1 H and 13 C NMR spectra in CD 3 OD, and FTIR and Raman spectroscopic techniques. The salts dissolve in organic solvents and water (pH = 7 to 3) even at high concentrations (10 −3 M). These solutions absorb light strongly from 500−300 nm. Solutions of 1, 3, and 4 fluoresce with high quantum yield in the 500−700 nm spectral range. Salts 1 and 4 exhibit fluorescence lifetime shortening, line width narrowing, and free-running laser action under intense pulsed laser excitation. Toxicity and cell imaging studies using human cancer cell lines reveal that salts 1 and 3 function as cellular fluorophores in vitro and have no adverse effects on cellular viability at nanomolar ranges. Furthermore, acetonitrile and methanol solutions of salts 1, 3, and 4 exhibit strong two-photon absorptioninduced fluorescence, opening potential applications in biomedical imaging and microscopy.