PHOTOCHEMISTRY OF SQUARAINE DYES .10. EXCITED-STATE PROPERTIES AND PHOTOSENSITIZATION BEHAVIOR OF AN IR SENSITIVE CATIONIC SQUARAINE DYE

The singlet and triplet excited-state behaviour of a cationic squarain e dye, (Sq) in acetonitrile is investigated using pico- and nano-secon d laser flash photolysis. The dye in its protonated form has absorptio n and emission maxima at 780 and 812 nm, respectively. The singlet exc ited state exhibits a difference absorption maximum at 640 nm and a li fetime of 1.1 +/- 0.1 ns. The triplet excited state, generated by T-T sensitization method exhibited a difference absorption maximum at 620 nm and a lifetime of 45 +/- 5 mu s. At higher laser excitation intensi ties, the dye underwent photoionization to yield a cation radical (abs . max. 630 nm). Photosensitization properties of the IR sensitive squa raine dye are demonstrated by modifying a nanocrystalline SnO2 electro de and exciting it with visible-IR light.