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

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