Ya. N. Malkin

Quantitative study of the photostability of spiropyrans

A quantitative method of determining the quantum yield of irreversible photodegradation (ϕC) of photochromic spiropyrans (SPP) was proposed for the first time. The ϕC of a large number of SPP of different types (with a different heterocyclic part) were determined. It was shown that for all of the SPP studied (except for dithiolane SPP), ϕC is almost independent of the heterocyclic part and is determined by the structure of the chromene part of the SPP. In addition to photodegradation, photooxidation takes place as a result of the reaction of the triplet state of the closed form of the SPP with O2 for nitrosubstituted SPP of all types. The value of ϕC is determined by the efficiency of the reaction of isomer X of the colored form with the solvent or impurities, i.e., the lifetime of this isomer.

The thermochromic and photochemical properties of bis-spiropyranes

1. The spectral properties of the indoline bis-spiropyrans are substantially different from the properties of the components of their monoderivatives. 2. In bis-spiropyrans with two open pyrane rings the absorption band is split into long wavelength and short wavelength components. 3. The ratio of the intensities of the short wavelength and long wavelength components is determined by the angle between the chromophores and corresponds to the theoretically calculated ratio.

Photodissociation of aromatic thiols and disulfides

For the first time, the quantum yields of cleavage of SS and SH bonds in a disulfide and a thiol and also the extinction coefficient of the photoinduced aminophenylthiyl radical were determined, on the basis of which the relation of the photodissociation quantum yield to the energy of an absorbed quantum was observed.

Role of the lower triplet state in photoreactions of aromatic amines

Conclusions1.The quantum yields of photodissociation of the simplest amines were determined and it was shown that the reaction of photodissociation of aniline takes place from the lower triplet state.2.The efficiency of photodissociation and the multiplet character of the excited state are determined by the ratio of the energy of the lower electron-excited states and the energy of cleavage of the N-H bond.

Spin-trapping study of radical products of photolysis of 1,2-dihydroquinolines

Conclusions1.Radicals formed during the photolysis of dihydroquinolines react with spin traps at two reactive centers.2.The constant of the interaction of the aminyl radical of 2,2,4,6-tetramethyl-1,2,-dihydroquinoline with C-phenyl-N-tert-butylnitrone has been determined.

Transformations of radicals during photolysis of 2,2-dimethyldihydroquinolines

Conclusions1.In solvents with a low electron affinity (hydrocarbons, alcohols) the photolysis of dihydroquinolines leads to cleavage of the N-H bond and to the formation of RN. radicals, which are capable of dimerization, and not to cleavage of the C-N bond and the formation of the o-quinone aldine structure.2.The low recombination rate of the RN. radicals is one of the reasons for the greater effectiveness of ethoxyquin as antioxidant.

QUANTITATIVE STUDY OF THE PHOTOSTABILITY OF SPIROPYRANS

A quantitative method of determining the quantum yield of irreversible photodegradation (ϕC) of photochromic spiropyrans (SPP) was proposed for the first time. The ϕC of a large number of SPP of different types (with a different heterocyclic part) were determined. It was shown that for all of the SPP studied (except for dithiolane SPP), ϕC is almost independent of the heterocyclic part and is determined by the structure of the chromene part of the SPP. In addition to photodegradation, photooxidation takes place as a result of the reaction of the triplet state of the closed form of the SPP with O2 for nitrosubstituted SPP of all types. The value of ϕC is determined by the efficiency of the reaction of isomer X of the colored form with the solvent or impurities, i.e., the lifetime of this isomer.

Photochemistry of spiropyrans of the dithiolane series with polycondensed chromene fragments

It has been shown on the basis of determinations of the values of the quantum yields of the photocoloration of spiropyrans of the 1,3-dithiolane and benzo1,3-dithiolane series that the annelation of a benzene ring in the chromene part of the molecule results in an increase in the efficiency of photocoloration and an increase in the stability of the merocyanine forms of the compounds investigated.

Determination of the quantum yields of the photochromism of spiropyrans with two chromene fragments

ConclusionsThe quantum yields of the photochromism of spiropyrans with two chromene functions have been determined. The combining of nitrochromene and benzochromene fragments in a single molecule results in an increase in the quantum yields of the photochromism of the benzochromene part of the molecules.

Photochemistry of spiropyrans of the dihydroisobenzofuran series

Conclusions1.A scheme of the photochemical transformations in photolysis of spiropyrans (SSP) of the dihydroisobenzofuran series was proposed: The elementary rate constants of formation of long-lived isomers of the merocyanine form were determined.2.Photodecolorization of the merocyanine form of SPP is also observed together with dark decolorization.3.The lower boundaries of the extinction coefficients of the photoinduced merocyanine forms and the upper limits of the quantum yields of photocoloration were estimated.