Spectroscopic and Theoretical Evidence for the Elusive Intermediate of the Photoinitiated and Thermal Rearrangements of Photochromic Spiropyrans

Abstract

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.

Metal complexes of the merocyanine form of nitrobenzospyran: Structure, optical spectra, stability

“…e MC data are available only for a few other spiropyrans. They were determined by photokinetic measurements carried out at different photon fluxes of the irradiating light [39,41,42], or by measuring simultaneously the NMR and absorption spectra of samples under UV irradiation [40]. The value of the association constants, K 2 , can be estimated if e MC is unknown from the temporal variation of the visible spectra of solutions prepared from the stable SP forms of spiropyrans and metal salts, in the dark and following UV irradiation [43].…”

Detailed Molecular Dynamics of the Photochromic Reaction of Spiropyran: A Semiclassical Dynamics Study

“…With the photon excitation, the electronic transitions vary with time. Before 86 fs, it can be seen in Figure 3 Table 3: Key geometry parameters for the dynamic simulation of photochromic ring-opening reaction of trans-SP (time in fs, bond distance in angstroms, and dihedral angles in deg) [41]. motion before 254 fs can be found to be the HOOP torsion of phenyl group nearby N atom as described in Figure 2(b).…”

“…using the model molecule [30][31][32][33][34][35][36][37][38][39][40][41]. There are three different pathways for the photochromic reaction proposed by computations.…”

Photo-and thermochromic spiranes 30*. Comparative study by X-ray structural analysis of the structure of spiropyrans of the indoline series containing a condensed furan fragment

“…Spiropyran 2c also displayed these properties in the solid phase, in thin films obtained by vacuum thermal spraying onto glass or quartz supports [2]. Unexpectedly it turned out that at lower temperatures (77 K) only in the case of compound 1 was the appearance observed of an absorption band with a maximum at 471 nm, which on prolonged irradiation is transformed into an absorption band with a maximum at 585 nm [3]. The spectral changes observed are linked with the formation in the first stage of the cis-cisoid X-isomer 1*, formed directly after fission of the C spiro -O bond, subsequent photoisomerization of which leads to the appearance of the trans-trans isomer 1* 2 .…”