Spectroscopic and theoretical evidence for the elusive intermediate of the photoinitiated and thermal rearrangements of photochromic spiropyrans.
Spectral properties and photochromic behavior of a series of novel 1',3',3'-trimethyl-1,2-tetramethylenespiro[7H-furo(3,2-f)-(2H-1)-benzopyran-7,2'-indolines] 1-4 have been studied. The mechanism of the photoinitiated ring-opening reaction involves the formation of an acoplanar cis-cisoid intermediate, the lifetime of which in the case of 6-(tert-butyl) derivative 4 is long enough to observe its absorption and fluorescence spectra under conditions of continuous irradiation. The occurrence of the intermediate on the reaction paths of the thermal and photochemical ring-opening processes has been also shown by the DFT and CIS calculations. The TD-B3LYP/6-31G//HF/6-31G calculated spectrum of the intermediate well matches that observed experimentally. For spiropyran 3 with a 6-NO(2) group, kinetic and activation parameters of the photoinitiated coloration and dark bleaching reactions have been determined.
Minkin
Vladimir I
VI
Institute of Physical and Organic Chemistry, Rostov University, Stachka Avenue 194/2, 344090, Rostov on Don, Russian Federation. minkin@ipoc.rsu.ru
Metelitsa
Anatoly V
AV
Dorogan
Igor V
IV
Lukyanov
Boris S
BS
Besugliy
Serguei O
SO
Micheau
Jean-Claude
JC