Subpicosecond pump–probe measurements of the electronic relaxation rates of the S1 states of azulene and related compounds in polar and nonpolar solvents

Publisher Website
Google Scholar
Abstract
The lifetimes of the S1 states of azulene, azulene‐d8, 4,6,8‐trimethylazulene, and guaiazulene (1,4‐dimethyl‐7‐isopropylazulene) have been measured in three nonviscous solvents of different polarity and structure using a two‐photon, two‐color, pump–probe method with subpicosecond time resolution. A significant solvent effect is measured. The rate constants for S1■S0 internal conversion in all four compounds in all three solvents exhibit one common S1–S0 energy gap law correlation, indicating that variations in the electronic relaxation rates are governed exclusively by changes in the Franck–Condon factors for the transition. No effect is observed when the exciting wavelength is changed, indicating that vibrational relaxation is occurring on a time scale which is faster than that of electronic relaxation in these systems. No significant deuterium isotope effect is measured in azulene, indicating that high frequency C–H(D) stretching vibrations do not act as significant accepting modes in the radiationless transition.