The skeletal photorearrangement including 6πelectrocyclization induced by UV light of ortho-halogen-substituted diarylethenes has been studied. It has been found that the reaction pathways leading to bi-or tricyclic frameworks depend on the kind of halogen substituent and solvent. Photocyclization with halogen abstraction leads to bicyclic fused aromatics, while the tricyclic frameworks are formed due to the tandem 6π-electrocyclization/ sigmatropic shift reaction. THF is preferred as the solvent in the former process and chloroform in the latter reaction. It was found for the first time that, owing to the ability of this series of diarylethenes to undergo skeletal photorearrangement with the release of the bromide cation, they can be used both as brominating agents and as Lewis acids for catalyzing electrophilic reactions.

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In recent years, great synthetic potential of the photorearrangement of diarylethenes leading to naphthalene derivatives via a cascade process of photocyclization/[1,n]-H shift/cycloreversion has been demonstrated. In this work, first a multifaceted study of the influence of various factors on the efficiency of the photorearrangement of diarylethenes of furanone series containing benzene and oxazole derivatives as aryl residues has been carried out. The efficiency of this phototransformation (quantum yields) and the effect of methoxy substituents in the phenyl moiety have been studied. Despite the multistage process, the quantum yields of the photorearrangement are rather high (0.34-0.49). It has been found that the efficiency of photocyclization of diarylethenes increases with the introduction of electron-donating methoxy groups in the phenyl moiety. Using the DFT calculations, we have been able to estimate in the photoinduced isomer the distance between hydrogen atom and carbon atom to which it migrates in the result of the sigmatropic shift. For all studied diarylethenes, this value was 2.67-2.73 Å, which is less than the sum of van der Waals radii of carbon and hydrogen atoms (2.9 Å).

The photo‐ and thermochromic behaviour of a series of spiro[indolinepyridobenzopyrans] 1–5 has been studied. The thermodynamic and kinetic parameters of the thermal equilibria between the ring‐closed and ring‐opened (merocyanine) isomeric forms of spiropyrans have been determined using UV–Vis absorption and 1H NMR spectroscopies techniques. The most stable form of 1‐(2‐hydroxyethyl)‐spiro[indoline‐pyridobenzopyran] 4 is represented by its trans‐(hydroxystyryl)oxazolidineindoline isomer coexisting in acetone solution with the ring‐closed spiroform. In the presence in solution of metal salts, spiro[indoline‐pyridobenzopyrans] exhibit strong ionochromic effect due to the formation of complexes with the merocyanine ligand. The composition of the complexes formed by Zn2+ and Ni2+ ions has been determined with the use of spectrophotometric and electrospray ionisation mass spectroscopy techniques. The stepwise stability constants and spectral properties of the most stable 1:1 and 1:2 metal/merocyanine complexes have been determined. Selectivity of the complexation reaction depends on the position of the thermochromic equilibrium. Copyright © 2007 John Wiley & Sons, Ltd.

In solution, the photochromic molecule 5‐methoxyspiro[indole‐phenanthrolinoxazine] (SPO) is in equilibrium with its corresponding merocyanine open isomer. In pure acetonitrile, there is about 22.5% of the open form, whereas in acetonitrile–water binary solvents this proportion increases to more than 60% when the water molar fraction χ(H2O) is around 0.80. Irradiation in the visible range leads to a photobleached steady state in which the proportion of the merocyanine open isomer decreases significantly. When irradiation is switched off, a slow thermal reversion of the closed spirooxazine to the open merocyanine takes place until the initial equilibrium position is reached. Kinetic analysis of a whole set of relaxation curves recorded at various water contents was used to establish a model involving multiple equilibria between three merocyanines in different solvation states (solvated by acetonitrile, solvated by an acetonitrile–water complex and hydrated). Their relative proportions, which are dependent on the binary mixture composition, were determined, in addition to their corresponding visible spectra. Copyright © 2004 John Wiley & Sons, Ltd.

The photochromic properties of a series of six 5-O-n-alkyl,6′-CN substituted spironaphthoxazines has been investigated in toluene and methanol solution. The6′-CN and 5-O-n-alkyl substitutions lead to a bathochromic shift of the UV spectra of the closed forms. Theλmaxof the visible spectra of the open forms decrease with solvent polarity. Most of the photochromic parameters have been quantitatively determined. Among them, photocoloration and photobleaching quantum yields and molar absorption coefficients of the open forms have been derived from a numerical fitting of the photokinetic curves recorded under continuous monochromatic irradiation. Results show that the photo-steady-state properties are relatively independent of the 5-O-n-alkyl chain length, but are more sensitive to the size of the indolinic nitrogen substituent.

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