Nadejda Sertova

Photochromism of styryl cyanine dyes in solution

Abstract The photochemical and spectral behavior of two styryl cyanine dyes were studied in different solvents. The experimental results indicate that in solution the compounds exist in two forms—closed and open. The equilibrium is strongly shifted toward the closed form. From the absorption and luminescence properties, the conclusion can be made that absorbed energy can be lost through different channels:photochemical closed—open form and cis—trans isomerization and through photophysical processes such as fluorescence. The quantum yield of the process, closed—open form is measured. The reasons for the photochromic behavior of these compounds are discussed.

PVC as photodonor of HCl for protonation of polyaniline

Abstract A novel photoinduced protonation of PANI(EB) from PVC as donor of HCl is proposed. The polymer-composite is a Polyvinylchloride (PVC) blended with the base form of polyaniline called emeraldine base (EB). The UV-induced protonation of the polymer chain is studied through its optical absorption. The protonation of EB occurs through HCl diffusion within the polymer chains in the PANI(EB)/PVC composite. After UV-exposure, the PANI(EB)/PVC-composite turns to green-color, which is typical of the emeraldine salt (ES). Contrary to film prepared from THF, a negative coloration is obtained with blends prepared from N -methylpyrrolidinone (NMP). Origin could be a proton-trapping effect from solvent traces behaving as usual PVC additives.

Photochemical behavior of poly(ethylacryloylacetate) and poly(acryloylacetone) films

Films of poly(ethylacryloylacetate) (PEAA) and poly(acryloylacetone) (PAA) were subjected to UV irradiation (λ = 254 nm) at room temperature. The photoinduced structure transfer from cis-enol onto a diketo forms has been investigated. The structure transfer caused by UV light was found to be slower than for the corresponding process in solution. The spectral investigations (UV, IR) showed reversible process of photoketonization. The results were analyzed in terms of the model for the participation of the trans-enol form in the process of the ketonization. Based on the results obtained, some general conclusions were made about the organization of the units in the polymer chain.

On the photosensitivity of poly (acryloylacetone) in solution

Abstract The influence of UV irradiation on the keto-enol ratio of poly (acryloylacetone) (PAA) in solution was examined. The tautomeric equilibrium is strongly displaced to the keto form. Important differences in the photosensitivity of the monomeric β-diketone (acetylacetone) (AA) and PAA were established depending on the structural features. The polymeric structure of PAA is an important parameter in the process. A possible route for the formation of the keto form is discussed.

Photoinduced ketonization of poly(ethylacrolylacetate) in solution

Abstract The influence of UV irradiation on the keto to enol ratio of poly(ethylacrolylacetate) (PEAA) in solution was examined. The major process is photoketonization, which is rapid and reversible. The role of the polymer chain is discussed in terms of its effect on the phototransformation. It is suggested that the high rate of photoketonization may be associated with the formation of sandwich complexes between the different units.

A New Pseudophotochromic Benzothiazoles Doped PVC Films

Abstract Under the influence of the UV light in 2-aryl substituted benzothiazoles doped PVC films take shapes, a new pseudophotochromic system. The coloured films were formed by two processes - the liberation of HCl during the photodegradation of PVC and an interaction between HCl and 2-arylsubstituted benzohiazoles (BT). They can return thermally to the colourless films and this process depends on the stability of the complexes BTH+.Cl−. Reversible photochromism was observed in the films on repeating irradiation with UV light. The experimental results, possible applications and future work on this pseudophotochromic system are also discussed.

Optically structured plastic electro-optic devices: about the particular photoinduced migration mechanism of bis-azodyes doped into polymers

Thin films of polymers containing photochromic azobenzene chromophores have been shown to be suitable materials for optical inscription. We report on surface relief gratings induced in poly(methylmethacrylate) thin-films doped with bis-azodyes. This brings some insight into the molecular migration mechanism which is responsible for the photoinduced surface relief grating formation.