A. V. Metelitsa

Luminescent complexes with ligands containing C=N bond

Data on luminescent complexes with azomethine ligands are generalized and systematized. The synthesis and luminescent properties of complexes with acyclic and cyclic azomethines are considered.

Role of structural flexibility in the fluorescence and photochromism of salicylideneaniline: the general scheme of the phototransformations

Abstract The mechanism of light-induced transformation in the salicylideneaniline molecule was studied by semiempirical PM3 calculations. The structures and energies of the minima and saddle points (transition states) on the S 0 , S 1 and T 1 potential energy hypersurfaces (PESs) were obtained, together with the gradient lines on the PESs. The structure-energy scheme was compared with the experimental findings. According to the results obtained, the following principle processes are observed: fast S 1 excited state intramolecular proton transfer (ESIPT), followed by typical ESIPT fluorescence; the formation of two S 1 twisted intramolecular charge transfer (TICT) structures which quench the ESIPT fluorescence; the diabatic formation of two ground state metastable coloured “post-TICT” structures responsible for photochromism.

Role of structural flexibility in fluorescence and photochromism of the salicylideneaniline: the “aldehyde” ring rotation

Abstract X-ray analysis, absorption and luminescent steady-state spectroscopy as well as quantum-chemical calculations have been used for comparative investigations of salicylideneaniline (i) an the more rigid phenylimine of 7-hydroxyindanine-1 (ii) molecules. In the latter the “aldehyde” ring A rotation is inhibited by inclusion of the saturated bridge fragment. Fluorescence with anomalous Stokes shift (ASS fluorescence) is typical for both (i) (only in glassy solvent) and (ii) (in liquid or glassy solvent). The ASS fluorescence occurs only as the result of excited-state intramolecular proton transfer (ESIPT). In liquid solvents the ESIPT in (i) may be followed by twisted intramolecular charge transfer (TICT) formation via adiabatic 90° ring A twist around the C AR C bond in the CN bond (Z)-isomer of the zwitterion NH structure. TICT state is one of the channels to quench the ASS fluorescence of (i) in the liquid solvent. The compound (ii) is found to have no photochromism unlike (i). The photochromism of the latter is connected not only with ESIPT but also with ring A 60–80° twist about the C AR C bond in the CN ( E )-isomer of the NH structure. It is proposed that the photocolored form originates from the concerted diabatic process (ring A twist and ( Z )-( E ) isomerization) competing with ASS fluorescence and the formation of the “TICT-like” structure.

The structural transformations and photo-induced processes in salicylidene alkylimines

Abstract The detailed comparative investigations of the mechanism of the fluorescent properties, formation and photochromic reaction in the salicylidene alkylimine (SALK) molecules with various N -Alk substituents and in corresponding more rigid model structures without C–Ph ring (A) twist have been carried out by the experimental and quantum-chemical methods. The crucial role of the A ring twist and the importance of the N -Alk substituent structure in the light-induced processes including the ESIPT, TICT formation, fluorescence with anomalous Stokes shift (ASS) and the formation of the metastable coloured so-called “post-TICT” structures has been shown. The mechanism of these processes is similar to that of the salicylidene aniline (SA) molecule but there are some important distinctions caused mainly by the lack of the l N –π Ph electrons interactions and also by the steric ones. In general the decrease of the photochromic efficiency and the increase of the ASS in comparison to the SA molecule are provoked by the SALK structures’ peculiarities.

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.

Synthesis, Photophysical and Redox Properties of the D–π–A Type Pyrimidine Dyes Bearing the 9-Phenyl-9H-Carbazole Moiety

Novel donor-π-acceptor dyes bearing the pyrimidine unit as an electron-withdrawing group have been synthesized by using combination of two processes, based on the microwave-assisted Suzuki cross-coupling reaction and nucleophilic aromatic substitution of hydrogen. Spectral properties of the obtained dyes in six aprotic solvents of various polarities have been studied by ultraviolet–visible and fluorescence spectroscopy. In contrast to the absorption spectra, fluorescence emission spectra displayed a strong dependence from their solvent polarities. The nature of the observed long wavelength maxima has been elucidated by means of quantum chemical calculations. The electrochemical properties of these dyes have been investigated by using cyclic voltammetry, while their photovoltaic performance was evaluated by a device fabrication study. The experimental and calculation data show that all of the dyes can be regarded as potentially good photosensitizers for dye-sensitized solar cells.

Metal complexes with azomethines containing the isomeric E-Z azo fragments

Cobalt and zinc complexes with phenylazosalicylaldehyde azomethines were obtained by chemical and electrochemical syntheses. The B3LYP/6-311G(d, p) calculations showed that the azo group in both the ligands and the complexes are mainly in the E-form.

Synthesis of Novel Iono- and Photochromic Spiropyrans Derived from 6,7-Dihydroxy-8-Formyl-4-Methyl-2H-Chromene-2-One

�-hydroxy group were synthesized and their spectral properties as well as abilities for complexation with metal ions studied. In solutions they exist as equilibrium mixture of spirocyclic (A) and merocyanine (B) isomers. The largest content of merocyanine form was found for the derivative with an electron-donating methyl group in position 5 of hetaryl fragment. The irradiation of SPPs in acetonitrile shifts the equilibrium to the B form. Similar effect causes the addition of metal cations due to formation of colored complexes with merocyanine isomers.

Solid state photochromism of spiropyrans

A series of spiropyrans possessing photochromic properties in solid state were investigated. UV irradiation (λmax=365 nm) of the thin vacuum deposited spiropyran films results in conversion of the colorless form to the photocolored one. The reaction is photochemically and thermally reversible. The photochromic activity of the solid material and polystyrene matrix has been compared. Raman spectroscopy has been used for studying the influence of metallic surface on the adsorbed spiropyran layers.

Electrochemical and Chemical Synthesis of New Luminescent Schiff Base Complexes

Bis-chelate complexes of zinc, cadmium, lead, and mercury with o-N-tosylbenzylidene imines containing the C7H15 and C18H37 substituents at the C=N group nitrogen atom were prepared by the methods of electrochemical and chemical syntheses. The structure of the azomethines and their complexes was established by the methods of heteronuclear 1H, 13C NMR spectroscopy (multidimensional and multinuclear COSY, HETCOR and HETCOR_LONG techniques). The complexes, as demonstrated by the X-ray analysis for the zinc chelate, have strongly distorted octahedral structure formed by the four azomethine nitrogen atoms and two oxygen atoms of the tosyl fragments. The coordination compounds show fluorescence in the blue part of the spectrum in high quantum yields for the zinc chelates.