Abstract

Pyranine or tsPyOH (8-hydroxy-1,3,6-trisulfonated pyrene) belongs to the family of aromatic alcohols which have been widely studied since Förster¹ and Weller². These molecules are known to undergo proton transfer (PT) both in the ground (GSPT) and singlet excited (ESPT) states, with Ka jump of seven orders of magnitude between the two processes. The dynamics of pyranine ESPT has been studied in various polar media ³-⁵. In all cases, ESPT was probed by observing the disappearance of the protonated species and the formation of the deprotonated form, using time resolved fluorescence techniques with picosecond or nanosecond time resolution. A long decay time (~100 ps) of tsPyOH^*, correlated with the formation time of tsPyO^-*, was found in aqueous solutions and ascribed to the ESPT time constant⁶. In contrast to these findings, Mataga's group, who probed ESPT of the related compound hydroxypyrene (PyOH) hydrogen-bonded to a strong base (triethylamine) in various non-polar and polar solvents, found a first, fast time constant (850 fs) followed by a slower one⁷. The first time constant, which is solvent independent, was ascribed to a fast ESPT, while the second one was assigned to the ion pair separation.

© 1996 Optical Society of America