Kinetics and mechanism of photochromic transformations of a 2,3-diarylcyclopentenone

Abstract

Photochemistry of recently synthesized 2,3 bis (2,5 dimethylthiophen 3 yl cyclopent 2 en 1 one) (diarylcyclopentenone, 1A) as a characteristic representative of photochromic 2,3 diarylcyclopent 2 en 1 ones (DCPs) was examined by means of stationary an nanosecond laser flash photolysis. Quantum yields of forward and backward photochemical reactions and molar absorption coefficient of the closed form were mea sured. Contradictions in the literature values of these parameters were eliminated. In laser flash photolysis experiments the formation of the 1A open form triplet state was exhibited, and the rate constants of the reactions of its decay were measured. 1A demonstrates rather low fatigue resistance, as any of other DCPs. In spite of the triplet state formation, photodegradation of 1A is not caused by the reactions of singlet oxygen.

Mechanistic Aspects of Photoinduced Rearrangement of 2,3-Diarylcyclopentenone Bearing Benzene and Oxazole Moieties

“…The spectrum of intermediate 2 (curve 1 in Figure ) contains the absorption band with the maximum in the region of 520 nm. The origin of this band is attributed to the system of conjugated π-electronic bands in 2 (Scheme C), similar to photoinduced isomers of the related photochromic diarylethenes. − Further transformation of 2 to 3 violates this conjugation and results in disappearance of the absorption band in the visible region.…”

“…The reaction mechanism includes three step: photocyclization, hydrogen shift, and disclosure of a heterocycle. However, the key intermediate 2 , which, by analogy with the photochromic diarylethenes of the cyclopentenone series, − had to exhibit an absorption band in the visible spectral region, was not registered either by UV spectroscopy or by 1 H NMR spectroscopy …”

Multifunctional fluorescent diarylethene: time-resolved study of photochemistry

“…17 Herein we report an in-depth study of photochemical properties for the selected switch D1 (Scheme 1) using nanosecond laser flash photolysis and ultrafast pump–probe spectroscopy for the quantitative description of the primary photophysical and photochemical properties. A comparison with previously reported data 18,19 for the parent DAE, DCP (Scheme 1), was performed, disclosing a more complicated mechanism of photochemical transformations for photoswitch D1 . Typically, electrocyclization of DAEs occurs in the picosecond time domain (see review 20 and references therein); the reaction is downhill and barrierless.…”

“…As for the microsecond time domain, the only intermediate absorption expected for photochromic DAEs seems to belong to the open form triplet state. 18,19,40,41 It should be noted that 6p-electrocyclization of DAEs via the triplet state occurring in the microsecond time domain is a fairly rare process. However, in several publications parallel singlet and triplet pathways of DAE photocyclization were reported.…”

“…19 The scheme illustrating DCP photophysics and photochemistry based on ref. 18 2a, b and c, d, respectively. Note that the absorption of short-lived intermediates in both solvents is superimposed with the bleaching caused by the disappearance of the initial compound.…”