Heteroatom substitution induced changes in excited-state photophysics and singlet oxygen generation in chalcogenoxanthylium dyes: Effect of sulfur and selenium substitutions

Photophysical properties of a series of tetramethylrosamine dyes in which the xanthylium oxygen atom has been replaced with sulfur or selenium were examined. Dyes with sulfur and, especially, with selenium show decreased fluorescence quantum yield and lifetimes, while at the same time proportionally larger increases in the rates of intersystem crossing lead to higher triplet yields (0.23 and 0.97, correspondingly). The selenium-containing dye (TMR-Se) displays prominent phosphorescence at 77 K and at room temperature when the solution is purged of oxygen. This is reflected in a high yield for singlet oxygen generation as shown by measurements of singlet oxygen phosphorescence. The high singlet oxygen yield for TMR-Se (0.87) suggests its use as an efficient photosensitizer for the generation of singlet oxygen in biology and chemistry applications.