PERPLEXING ASPECTS OF THE TWO PHOTON CHEMISTRY OF ROSE BENGAL

Christopher R. Lambert*, Irene E. Kochevar** and Robert W. Redmond**

*Chemistry Department, Connecticut College, 270 Mohegan Avenue, New London, CT 06320

**Wellman Laboratories of Photomedicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, U.S.A.

Correspondence: Christopher R. Lambert ..... crlam@conncoll.edu

Irene E. Kochevar ..... kochevar@helix.mgh.harvard.edu

Robert W. Redmond ... redmond@helix.mgh.harvard.edu

Keywords: photosensitization; rose bengal; non-linear photochemistry; two-photon

Abstract

Two photon laser flash photolysis has been used to investigate the upper excited state chemistry of rose bengal. The rose bengal triplet state, generated using 532 nm irradiation, has been monitored as a function of wavelength of the second photon. The second pulse is derived from a tunable OPO laser which allows for excellent selectivity in the excitation of the transient intermediate. It is found that the triplet state bleaches when only the triplet state absorbs the second photon however, no bleaching is observed when there is significant ground state absorption at the wavelength of the second photon. It is possible that the difference in the two experiments described, arises because of an experimental artifact or because the two photon chemistry is wavelength dependent.