Table of Contents
Laser Chemistry
Volume 19, Issue 1-4, Pages 375-379
http://dx.doi.org/10.1155/1999/37692

Direct Observation of S2–S1 Internal Conversion in Pyrene by Femtosecond Transient Absorption

1LENS, Largo E. Fermi 2, Florence 50125 , Italy
2Dipartimento di Chimica, via G. Capponi 9, Florence 50121, Italy

Received 11 April 1997

Copyright © 1999 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

UV pulses of 100 fs at 340 nm are utilised to excite pyrene to the vibrationally cold S2 state. Population and depopulation processes occurring in the S2 state are investigated by transient absorption spectroscopy with a white continuum probe. In the first 400 fs after excitation it is possible to measure the growth and disappearance of a band at 585 nm which is assigned to the S14←S2 transition. As a consequence of the internal conversion process from S2 to S1 state, the disappearance of the 585 nm band and the growth of the transient spectrum due to Sn←S1 transitions can be observed. Kinetic measurements of the S2 decay and S1 growing signals provide an estimate of the rate of internal conversion which occurs with a time constant of 150±50 fs.