Table of Contents
Laser Chemistry
Volume 1, Issue 5, Pages 357-386
http://dx.doi.org/10.1155/LC.1.357

Picosecond Absorption Spectra and Relaxation Processes of the Excited Singlet State of Pyrene in Solution

Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan

Copyright © 1983 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The method of analysis for the ps transient absorption spectra obtained by a ps Nd3+: YAG laser photolysis system is described in detail, showing the results of pyrene in solution. The SnS1 spectrum observed immediately after excitation is rather broad and its intensity in the short wavelength region is relatively enhanced, compared to the spectrum observed at later stages. For elucidating this fast spectral change, the spectrum at 0 ps was simulated from that at 100 ps, evaluating numerically the inner filter effect, depletion of the ground state molecules and temporal characteristics of the monitoring ps continuum. The difference between the simulated and experimentally observed spectra may be ascribed to the nonlinear refractive index change of the solvent, the thermal lensing effect, or to an intrinsic relaxation of the excited molecule. Examining absorption spectra obtained under various conditions, the former two possibilities were denied for the excited pyrene system. Vibrational relaxation as well as the S2S1 internal conversion with a time constant of less than 10 ps have been suggested to be responsible for this difference between the simulated and observed spectra.