Photochemistry of squaraine dyes. Part 10.—Excited-state properties and photosensitization behaviour of an IR sensitive cationic squaraine dye

Abstract

The singlet and triplet excited-state behaviour of a cationic squaraine dye, (Sq) in acetonitrile is investigated using pico- and nano-second laser flash photolysis. The dye in its protonated form has absorption and emission maxima at 780 and 812 nm, respectively. The singlet excited state exhibits a difference absorption maximum at 640 nm and a lifetime 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 µs. At higher laser excitation intensities, the dye underwent photoionization to yield a cation radical (abs. max. 630 nm). Photosensitization properties of the IR sensitive squaraine dye are demonstrated by modifying a nanocrystalline SnO₂ electrode and exciting it with visible–IR light.