It was shown by electron absorption spectroscopy and X ray diffraction analysis that steric strains in photochromic 2 (N acyl N arylaminomethylene)benzo [b]thiophen 3(2Н ) one mol ecules ortho substituted in the N phenyl ring increase the quantum yield of the N→O photo induced rearrangement in accord with an increase in the steric constant of the ortho sub stituent.✾ Photochromism of 2 (N acyl N arylaminomethyl ene)benzo[b]thiophen 3(2Н ) ones (1) is based on photo initiated Z/E isomerization relatively to the С=С bond followed by the thermal N→O migration of the acyl group (Scheme 1). 1,2Compounds of this type (λ max (1) > λ max (2)) are of interest as systems with negative photochromism, 3,4 whose molecules can accumulate the light energy released dur ing the catalytically controlled process 2 → 1. A wide vari ability of their structures also predetermined a possibility of using ketoenamines 1 as chemosensors for metal cat ions 5,6 (1e), molecular switches of an optical signal 7 (1f), and fluorescent sensors for a change of the pH of a me dium 8 (1g) acting according to principle of the РЕТ ef fect. 9 Reasons for the appearance of chiral properties of ketoenamines 1 ortho substituted in the N phenyl ring were studied. 10 The examples presented show that the structure of a molecule of the type 1, in particular, spatial interactions between the N aryl and N acyl substituents and the heterocyclic moiety, can exert a determining ef fect on the spectral luminescence properties and photo chromism of these compounds. Nevertheless, a relation ship between steric interactions in the ground state in molecules of this type and their spectral and photochemi cal properties (λ max , ε max , λ b ,* ϕ 1→2 ) has not been studied up to date. It can be useful to establish such a relationship for design of chiral chemosensors or switches of an optical signal. According to this, the following tasks of the present Scheme 1 * Long wave absorption boundary λ b with ε ≈ 1.0 L mol -1 cm -1 .
Photochromic substances T 2200 Synthesis and Properties of Photoacylotropic (2Z)-2-(N-Acyl-N-arylaminomethylidene)benzo[b]thiophen-3(2H)-ones with a Chiral MigratingGroup. -Irradiation of new photochromic title benzothiophenones containing L-amino acid moieties as migrating groups (III) results in a photo-induced acyclotropic rearrangement N→O accompanied by migration of the chiral fragment. -(RYBALKIN*, V. P.; VOROB'EVA, Y. Y.; BORODKIN, G. S.; DUBONOSOV, A. D.; TSUKANOV, A. V.; TKACHEV, V. V.; ALDOSHIN, S. M.; BREN', V. A.; MINKIN, V. I.; Russ.
New photochromic (2Z ) 2 (N acyl N arylaminomethylidene)benzo[b]thiophen 3(2H ) ones containing L amino acid derivatives as migrating groups were synthesized. Light irradia tion of their solutions at 436 nm leads to the photoinduced acylotropic rearrangement N → O accompanied by migration of the chiral fragment. The bulky N acyl group causes steric strain thus destabilizing the amide form of compounds and facilitating the photorearrangement.
benzo[b]thiophen-3(2H)-ones. -Photochromic ketoenamines (I) and (II) of the benzothiophene series are studied by H NMR spectroscopy and X-ray diffraction analysis. Introduction of a bulky substituent into the ortho-position of the phenyl ring of the amine fragment in (I) and (II) yields stable chiral structures due to hindered rotation of the phenyl ring. The energy barrier to racemization is sufficiently high for the preparative resolution of enantiomers. -(RYBALKIN*, V. P.; SHEPELENKO, E. N.; VOROB'EVA, Y. Y.; BORODKIN, G. S.; BREN', V. A.; MINKIN, V. I.; ALDOSHIN, S. M.; TKACHEV, V. V.; UTENYSHEV, A. N.; Russ.
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