Vladimir Lokshin

Synthesis and unexpected photochemical behaviour of biphotochromic systems involving spirooxazines and naphthopyrans linked by an ethylenic bridge

Abstract Using the Wittig reaction, six new biphotochromic compounds have been prepared by the coupling of conveniently functionalised spiro[indoline–naphthoxazines] and naphthopyrans. Compared to molecules taken individually, unusual photochromic behaviour has been detected with compounds for which a double bond of Z -configuration links both entities by the 5 or 5′ positions of the naphthalenic parts. Indeed, in this case the thermally stable uncoloured and coloured forms (bistable system) can be photochemically converted acting as photochemical switches.

Synthesis and reactivity of formyl-substituted photochromic 3,3-diphenyl-[3H]-naphtho[2,1-b]pyrans

Synthetic accesses to formylated photochromic 3,3-diphenyl-[3H]-naphthopyrans (or 2H-benzochromenes) are developed through classical cyclization between appropriate hydroxynaphthaldehydes and 1,1-diphenylpropyne-1-ol and also via substituent transformations on the naphthopyran skeleton including bromine/lithium exchange and the oxidation of an hydroxymethyl group. Examples of formyl group reactivity (Wittig and Knoevenagel reactions, imine formation) from these compounds are given, showing their interest in the subsequent preparation of supramolecular systems involving a photoreactive entity.

Effect of heteroaromatic annulation with five-membered rings on the photochromism of 2H- [1] -benzopyrans

Abstract Photochromic properties (colorability, UV-VIS spectra of photo-merocyanines, rate constant of thermal bleaching) of chromenes annulated with different five-membered azaheterocycles or with furan cycles were investigated under flash photolysis. All the compounds, i.e., the 7H-pyrano[2,3-g]benzazoles 4–6, the 7H-pyrano[3,2-e]benzazoles 7–10, the 7H-pyrano[3,2-e]indoles 11–12, the 3H-pyrano[3,2-a]carbazole 13, the 8H-pyrano [2,3-e] indole 14 and the 3H-furano [ 3,2-f]chromenes 15–18 undergo reversible photochromic reaction at room temperature. They are compared with naphthopyranic parents 1–3. Whatever the structure of the heteroaromatic moiety, the annulation of the benzopyrans leads to the splitting into two bands of the electronic absorption spectra of the photoinduced forms with a significant bathochromic shift, a feature of interest for variable optical absorption systems. Unfortunately, diaryl-substituted azolo-fused chromenes exhibit decreased colorabilities. Furofused benzopyrans are particularly interesting with respect to naphthopyran parents owing to the bathochromically shifted and broadened absorption spectra of photoinduced forms and slightly enhanced colorabilities.

Effect of metal cations on the photochromic properties of spironaphthoxazines conjugated with aza-15(18)-crown-5(6) ethers

Spironaphthoxazines conjugated with aza-15(18)-crown-5(6)-ether moieties at the 6′-position of the naphthalene fragment (Crown-containing Spironaphthoxazines, CSN) were synthesised and studied for the first time. The addition of Li+ and alkaline earth (Mg2+, Ca2+, Sr2+ and Ba2+) metal cations to CSN solutions results in a hypsochromic shift of the UV absorption band of the spiro form and a bathochromic shift of the absorption band of the merocyanine form in the visible region. In addition, the equilibrium shifts to the merocyanine form, and the lifetime of the photoinduced merocyanine form increases. Analysis of the spectral and kinetic data allows a complexation scheme to be proposed and the stability constants of the resulting complexes to be calculated. According to the results obtained, the complexation with Li+ and alkaline earth metal cations in acetonitrile initially involves the crown ether moiety; the participation of the merocyanine oxygen atom in the complexation process occurs at a high metal cation concentration. The UV-induced isomerisation of CSN into the merocyanine form causes a decrease of the cation binding ability.

Photochromism and solvatochromism of push???pull or pull???push spiroindolinenaphthoxazinesElectronic supplementary information (ESI) available: Analysis of products 12, 13, 14 and 17 absorbance of solutions of 2. See http://www.rsc.org/suppdata/b2/b204603b/

The photochromic and solvatochromic behaviour of 17 variously substituted spiroindoline naphthoxazines has been investigated in cyclohexane, toluene, acetonitrile and methanol in fluid solution. Specific parameters such as the wavelengths and the molar absorption coefficients of the closed spiro- and open merocyanine forms, together with the photocoloration and photobleaching quantum yields, rate constants and activation energies of thermal fading have been determined under continuous monochromatic irradiation. It has been shown that most of these parameters are closely related to the electron distribution on the highly conjugated photomerocyanines and on their quinoidal or zwitterionic character. Depending on the acceptor or donor properties and on the position of their substituents, three classes of compounds have been detected.

Practical synthesis of 8-acyl-7-alkyl-1,6-naphthyridin-5(6H)-ones

Reaction of a set of enaminones with 2-chloronicotinoyl chloride or 2,6-dichloro-5-fluoronicotinoyl chloride mainly leads to N-acylation products which cyclize directly or reacting with sodium hydride to give 8-acyl-7-alkyl-1,6-naphthyridin-5(6H)-ones. Due to their easy availability these compounds are attractive precursors for synthesis of polycondensed heterocycles like naphtho[2,3-h][1,6]naphthyridin-5-ones and pyrido[3,2-c][1,6]naphthyridin-6-ones.

First permanent opened forms in spiro[indoline-oxazine] series: synthesis and structural elucidation

The geometrical structure (TTC isomer), as well as the electronic distribution (quinoidic form), of the first permanent opened forms of spirooxazines 5a and b have been determined by 1H NMR spectroscopy and dipole moment measurements. The crystal structure of compound 5b has been determined by X-ray diffraction to confirm the conformations. Molar absorption coefficients were found to be 4.8 × 104 and 4.9 × 104 dm3 mol–1 cm–1, respectively, for 5a and b.

New Photochromic 2,2-Diphenyl-[2H]-Chromenes Annellated With Nitrogenated Sex-Membered Ring

Abstract New photochromic 2,2-diphenyl-[2H]-chromenes 1–6 annellated with nitrogenated six-membered ring have been synthetized by optimized reaction of suitable metal phenolates and β-phenyl cinnamaldehyde. All compounds exhibit photochromic behavior at room temperature. Chemical yields and photochromic characteristics depend significantly on the relative position of annellation on the chromenic moiety.

Influence of DNA-binding on the photochromic equilibrium of a chromene derivative

The photochromic properties of a chromene derivative, which contains a positively charged substituent, were investigated in the presence of ct DNA. Upon irradiation in the absence of DNA the colored quinoid open form is highly unstable and rapidly reverts back to the initial closed form (bleaching). In the presence of DNA the open form is significantly stabilized, presumably because of the association with the macromolecule. The kinetics of the bleaching reaction of the bound ligand were determined and employed to estimate the binding constant.

Studies of polyphotochromic behaviour of supermolecules by NMR spectroscopy. Part 1. A bis-spirooxazine with a (Z)-ethenic bridge between each moiety

The photoproducts resulting from the irradiation of a closed colourless biphotochromic molecule formed by two spironaphthoxazine entities linked through an ethenic bridge and its model compound, a singular spironaphthoxazine joined by a double bond to a 2-methoxynaphthalene nucleus in the Z configuration have been studied by high resolution 1H NMR spectroscopy. At low temperature, a clean conversion between closed and open structures has been observed with the demonstration of mono and bi opening of the biphotochromic molecule. In contrast, studies at ambient temperature have implied an irreversible loss of the photochromic properties, with the formation of diastereoisomers, resulting from the cyclisation-oxidation reaction of the systems. But, by carrying out experiments on degassed samples, a significant reversion to closed initial structures was observed.