Bright NIR-Emitting Styryl Pyridinium Dyes with Large Stokes ' Shift for Sensing Applications

Two NIR-emitting donor-pi-acceptor (D-pi-A) type regioisomeric styryl pyridinium dyes (1a-1b) were synthesized and studied for their photophysical performance and environment sensitivity. The two regioisomers, 1a and 1b, exhibited interesting photophysical properties including, longer wavelength excitation ( lambda(ex) approximate to 530-560 nm), bright near-infrared emission ( lambda(em) approximate to 690-720 nm), high-fluorescence quantum yields ( phi(fl) approximate to 0.24-0.72) large Stokes ' shift (Delta lambda approximate to 150-240 nm) and highenvironmental sensitivity. Probe ' s photophysical properties were studied in different environmental conditions such as polarity, viscosity, temperature, and concentration. Probes (1a-1b) exhibited noticeable changes in absorbance, emission and Stokes ' shift while responding to the changes in physical environment. Probe 1b exhibited a significant bathochromic shift in optical spectra (Delta lambda approximate to 20-40 nm) compared to its isomer 1a, due to the regio-effect. Probes (1a-1b) exhibited an excellent ability to visualize bacteria (Bacillus megaterium, Escherichia coli), and yeast (Saccharomyces cerevisiae) via fluorescence microscopy.