Time-Resolved Absorption Studies on the Photochromic Process of 2H-Benzopyrans in the Picosecond to Submillisecond Time Domain

Yoichi Kodama, Takakazu Nakabayashi, Katsunori Segawa, Emi Hattori, Masako Sakuragl, Nobuyuki Nlshi, Hirochika Sakuragi

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Picosecond to submillisecond photochromic reactions of 2,4-diphenyl-2H-benzopyran and 2,2,4-triphenyl-2H-benzopyran have been investigated by time-resolved absorption spectroscopy. The C-O bond cleavage of the benzopyrans (closed forms) occurs via the first excited singlet state within 2 ps to produce vibrationally excited open forms in the ground electronic state. In the subnanosecond to submillisecond time domain, several decay components with almost the same spectral profiles are observed. These components are assigned to respective stereoisomers with respect to two double bonds and one single bond of the open enone forms. From the pump-laser power dependencies of the yields of the open forms, it is suggested that the photocleavage gives at first only the open forms revertible to the closed form by a single-bond rotation, and that the photoexcitation of the first generated open forms gives rise to other open forms which need a double-bond rotation for reversion to the closed form. The photochromic reactions of a series of 2H-benzopyrans bearing substituents on the pyran ring have also been studied using nanosecond time-resolved absorption spectroscopy. The size of a substituent in the 4-position fairly affects the rate constants of the thermal reversion of the open form to the closed form.

Original languageEnglish
Pages (from-to)11478-11485
Number of pages8
JournalJournal of Physical Chemistry A
Volume104
Issue number49
DOIs
Publication statusPublished - 2000 Dec 14
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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