N. V. Volbushko

Novel Spiropyrans With the Luminescent Larle in the 2H-Chromene Fragment

Abstract A series of novel spirobenaopyrans containing the fluorescent label, 3,5-diphenyl pyrazoline substituent, in the position 7 of the 2H-chromene fragment, has been prepared. The compounds display high efficiencies of the fluorescence (460–490 nm) and have a potential for application as negative luminescent materials for optical storage.

Structures and photo- and thermochromic properties of spiropyrans of the 2-oxaindan series with polycondensed chromene fragments

Spiropyrans of the 2-oxaindan series with 2H-chromene fragments benzo- and 2,3-naphthoannelated at the 7–8 bond were synthesized. The molecular structures of four of the spiropyrans obtained were determined by x-ray diffraction studies, and their photo- and thermochromic properties were studied. Annelation of arene rings significantly increases the relative stabilities fo the photocolored forms of the spiropyrans. A correlation between the length of the Cspiro-O bond and the capacity of spiropyrans for photocoloration was discovered. In addition, the free energies of activation of the thermochromic transformations of spiropyrans determined by dynamic NMR spectroscopy are insensitive to variations in the length of the indicated bond.

Photochromic coumarin spiropyrans

New photochromic spiropyrans (SPP) derived from 4-methyl-7-hydroxy-8-formylcoumarin have been synthesized. The effect of the heterene fragment on the spectral and photochromic properties of the SPP was examined. The photoproduct of the benzodithiolane SPP had the absorption with longest wavelength. Indoline SPP were found to have the most efficient photocoloring. Fluorescence of the cyclic form was found for the SPP.

Photochemistry of 2-amino-2H-benzochromenes

Diabatic photoinduced ring opening of the chromene ring of 2-amino-5,6-benzo-2H-chromenes and 2-amino-6-methyl-7,8-benzo-2H-chromenes leads, in the same way as a thermally induced reaction, to the establishment of ring-chain tautomer equilibrium in the ground electronic state, the position of this equilibrium depending on the polarity of the solvent, the temperature, and structural factors. o-Quinoid tautomers exist as several stable isomeric forms: an acoplanar cis-S-cis-trans-form absorbing in the shortwave region, and S-trans-isomers absorbing in the longwave region of the spectrum. Photoexcitation of the o-quinoid forms in the temperature range 125–190 K initiates mutual conversions of these and the initial 2H-chromene structure. The relative stability of the conformers of the o-quinoid form depends on steric and electronic factors: benzanellation in positions 5,6 leads to stabilization of the cis-S-cis-trans-isomer and in positions 7,8 the S-trans-isomers are more preferred: π-acceptor substituents on the amine component increase the stability of the cis-S-cis-trans isomer and electron-donor substituents stabilize the S-trans-isomer.

Mechanism of the photoreactions of fulgides based on 1,2-dimethyl-3-formylindole

Only E ⇄ Z isomerization is observed for the steady irradiation of fulgides based on 1,2-dimethyl-3-formylindole in contrast to the analogs based on 3-acetylindole. The formation of cyclic photoisomers is registered by the method of impulse photolysis. The presence of a methyl substituent in the position 2 of the indole portion leads to a significant increase in the stability of the photochromic system. The introduction of alternative reaction centers of cyclization in the form of bulky phenyl groups leads to the suppression of electrocyclization at the position 2 of the indole portion and the formation of dihydronaphthalene structures.

Energetics and structural mechanisms of photochemical processes in molecules of aldonitrone vinylogs

Depending on the multiplicity of the excited state, alternative photoreactions are realized in methoxy and acetoxy derivatives of aldonitrone vinylogs: diabatic nitrone-oxazypyridone rearrangement in the first excited singlet state and E-Z isomerization involving the C=N bond in the triplet state. In the case of aldonitrone vinylogs with an o-hydroxy group in the α-aryl ring one observed adiabatic proton transfer from the hydroxy group to the azotoxido group with a subsequent diabatic reaction involving cyclization to the 2H-chromene structure. The same transfer is also realized in the triplet state. The quantum yields were determined, and the energies of activation of the photoreactions and the reverse thermal processes were evaluated.

Structure and photochromic transformations of fulgides of the indole series

Previously undescribed fulgides of the indole series, viz., (1-methyl-3-indolylmethylene)- and (1-methyl-3-indolylethylidene) (isopropylidene)succinic anhydride, were synthesized. A Z conformation for (1-methyl-3-indolylmethylene) (isopropylidene)succinic anhydride and an E configuration for (1-methyl-3-indolylethylidene)-(isopropylidene) succinic anhydride were established by electronic and PMR spectroscopy and x-ray diffraction analysis. The photochromic properties of fulgides were observed and investigated. A scheme of photoinduced and thermal transformations of fulgides that includes a step involving Z → E isomerization in the excited state is proposed. An additional photoisomer was recorded by pulse photolysis and fluorescence.

Ring-chain tautomerism and thermo- and photochromism of 3-(1-hydroxy-4-methyl-2-naphthyl)propenal imines

A series of previously undescribed 3-(1-hydroxy-4-methyl-2-naphthyl)propenal imines was synthesized. In the crystalline state all of the imines, except the N-(p-nitrophenyl)imine, have an open o-quinoid structure, whereas in solutions in nonpolar solvents they exist in the cyclic 2H-chromene form. In polar solvents the imines display ring-chain tautomeric equilibrium of the 2H-chromene and o-quinoid forms, the relative percentages of which are determined by the character of the substituent in the amino component of the molecule and by the polarity of the solvent. The N-(p-nitrophenyl)imine has-the 2H-chromene structure in the solid phase and in solvents.