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.     

Spiropyrans and spirooxazines. 2. Synthesis,structures, and photochromic properties of 6"-cyano-substituted spironaphthooxazines

A series of 6"-cyano-substituted spiro[indoline-2,3"-naphtho[2,1-b]oxazines] containing substituents with carbon chains of different lengths in the indoline fragment were synthesized. The structure of one of these spironaphthooxazines was established by X-ray diffraction analysis. The influence of substituents on the photochromic properties of the resulting compounds in solutions and polymeric films was studied.     

The structural transformations and photo-induced processes in salicylidene alkylimines

The detailed comparative investigations of the mechanism of the fluorescent properties, formation and photochromic reaction in the salicylidene alkylimine (SALK) molecules with various N-Alk substituents and in corresponding more rigid model structures without C–Ph ring (A) twist have been carried out by the experimental and quantum-chemical methods.

The crucial role of the A ring twist and the importance of the N-Alk substituent structure in the light-induced processes including the ESIPT, TICT formation, fluorescence with anomalous Stokes shift (ASS) and the formation of the metastable coloured so-called “post-TICT” structures has been shown. The mechanism of these processes is similar to that of the salicylidene aniline (SA) molecule but there are some important distinctions caused mainly by the lack of the l_N–π_Ph electrons interactions and also by the steric ones. In general the decrease of the photochromic efficiency and the increase of the ASS in comparison to the SA molecule are provoked by the SALK structures’ peculiarities.     

Novel photochromic spirocyclic compounds of thienopyrroline series: 2. Spirooxazines

Photochromic properties of novel spirooxazines of the thienopyrroline series have been studied in comparison with those of an indoline analogue. Solvatochromism of the merocyanine photoisomers has been investigated using the Kamlet–Taft model. It has been found that inversion of the trends in the solvatochromic behavior of the spirooxazines takes place when passing from non-protogenic to protic solvents. Thienopyrroline spirooxazines possess relatively poor fatigue resistance. The origin of the processes causing their photodegradation has been studied.     

Spiropyrans and spirooxazines. 1. Synthesis and photochromic properties of 9"-hydroxy- and 9"-alkoxy-substituted spironaphthooxazines

A procedure was developed for phase-transfer catalyzed alkylation of 5-hydroxyindolenine and 9"-hydroxy-substituted spiro[indoline-2,3"-naphtho[2,1-b]oxazines] by alkyl halides. New 9"-hydroxy- and 9"-alkoxy-substituted spironaphthooxazines, spirooxazinyloxyacetic acids, and their esters containing substituents with different length of the carbon chain in the indoline moiety were synthesized. The influence of the substituents on the spectroscopic properties of the starting and colored forms and the kinetic characteristics of photochromic transformations of 9"-substituted spironaphthooxazines in solutions and polymeric films was investigated. The bipolar merocyanine forms of spirooxazines were found to produce H-aggregates.