The results of investigations of the properties of cyanine dye dimers in the triplet state are presented. The formation of dimers is demonstrated as two absorption bands of differing intensities, which are due to splitting of the S*-level of monomers as a result of their resonance interaction. The cyanine dye dimers are characterized by a relatively high quantum yield of the intersystem crossing. In the triplet-triplet absorption spectra two bands appear, where the long-wavelength band is assigned to a charge transfer state. The cyanine dye dimers in the triplet state are involved in the energy and electron transfer and can act as the photosensitizes of redox reactions.

The dark process (posteffect) of increasing the electrical conductivity and spectral absorption in the graphene oxide (GO) film after its preliminary UV irradiation has been studied. The posteffect is due to the conformational relaxation of the structure (flattening) of GO nanosheets after the UV-induced dissociation of oxygen-containing groups. At room temperature, the relaxation time is τ ≈ 300 h and the activation energy in the range of 20–70°C is E a ≈ 0.6 eV.

Spectral, luminescent and time-resolved characteristics of 2,5-dibenzylidenecyclopentanone and its symmetrical derivatives (bis( N,N -diethylamino-), dimethoxy-, tetramethoxy-, dimethylthio-, and bis-18- crown-6 derivative) have been studied in media of different polarity (cyclohexane, toluene, acetonitrile, DMSO, and methanol) at room temperature. The absorption maximum of dibenzylidenecyclopentanone shifts bathochromically by 15 nm with an increase in polarity of the medium (cyclohexane–methanol). The introduction of electron-donating substituents in the aromatic rings of dibenzylidenecyclopentanone also results in a bathochromic shift of the absorption maximum by 100–130 nm in the media of different polarity and shifts the fluorescence maximum by 130 nm relative to the maximum of the dimethoxy derivative. Upon laser irradiation of oxygen-free solutions of dibenzylidenecyclopentanone and its tetramethoxy- and bis-18-crown-6 derivatives in acetonitrile, the triplet state with a half-life time of 0.3–1 μs is generated. For dimethoxy-, dimethylthio-, tetramethoxy-, and bis-18-crown-6 derivatives of dibenzylidenecyclopentanone, the isomers with a lifetime of ~50 ms are formed.

Spectral properties of inclusion complexes of cucurbit[7]uril (CB[7]) with styryl dye dications containing N-ammonioalkyl substituents of various length (D1, D2, D3) in water have been studied. The optimized structures of these complexes calculated by DFT methods made it possible to correlate the observed effects with the position of the nitrogen atom of the pyridinum residue of styryl dyes with respect to the CB[7] cavity. The bathochromic shifts of long-wavelength absorption bands for the inclusion complexes of D1 and D2 and the absence of such a shift for D3 are caused by structural distinctions between the inclusion complexes.

Исследовали спектральные свойства комплексов включения кукурбит[7]урила (CB[7]) с дикатионами стириловых красителей с N-аммониоалкильными заместителями различной длины (D1, D2, D3) в воде. Рассчитанные квантово-химическими методами DFT оптимизированные структуры этих комплексов позволили связать наблюдаемые эффекты с положением атома азота пиридиниевого остатка стириловых красителей относительно полости CB[7]. Батохромные сдвиги длинноволновых полос поглощения для комплексов включения D1 и D2 и отсутствие такого сдвига для D3 обусловлены структурными различиями комплексов включения.

Thiacarbo- and thiadicarbocyanine indolenine and thiazoline polymethine dyes form host‒guest complexes with cucurbit[7,8]urils in water. Cucurbit[7]uril forms preferentially 1: 1 and 1: 2 monomeric complexes and cucurbit[8]uril forms 2: 1 and 2: 2 dimeric complexes. On the basis of quantum-chemical calculations, the structure of monomeric and dimeric complexes has been suggested. The complexation manifested itself in absorption, prompt and thermally activated delayed fluorescence spectra, as well as in the triplet‒triplet absorption spectra. Dimeric complexes in the triplet state are involved in one-electron oxidation and participate in triplet‒triplet energy transfer.

Alkylsubstituted thiacarbocyanines (3,3′-diethylthiacarbocyanine, D1 , and 3,3′-disulfopropylthiacarbocyanine, D2 ), existing in water as monomers and dimers, manifest the ability to transition to the triplet state. The spectrum of triplet-triplet (T–T) absorption of the D2 dimers is shifted in the range higher than 590 nm by 20 nm to the red in comparison with the T–T spectrum of monomers. The D1 dimers in the presence of cucurbit[8]uril form a dimeric complex with two bands in the differential absorption spectrum. The band at 550 nm belongs to the triplet-triplet absorption of the dimeric complexes, and the band in the range of 620–700 nm is the result of charge transfer in the triplet state. The rate constants of deactivation for these triplet states coincide.

Models of quantum-chemical calculation of rate constants for internal processes and intersystem crossing in polyatomic molecules are considered. The influence of the nature of electronically excited states in organic compounds is investigated. It is shown that the explicit allowance for the nature of wave functions of electronic states for estimation of electronic matrix elements of nonadiabaticity operators and spin-orbit interaction allows photophysical processes in organic compounds to be considered in detail.

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone (CH1) and its bis(aza-18-crown-6) derivative (CH2) in acetonitrile at ambient temperature and 77 K have been studied. The absorption, fluorescence, and phosphorescence spectra of CH1 and CH2 are similar. The probability of the formation of the triplet state is higher for CH2 molecules (λT-T max = 660 nm, lifetime τT ~ 20 μs). The lifetime of the CH1 molecule in the triplet state is estimated at τT ~ 2–3 μs. Photoisomers of CH1 and CH2 are formed along with the triplet state. According to DFT calculation results, the formation of trans–cis photoisomers of CH1 and CH2 is the most energetically favorable.

Experimentally revealed features of thermal and photochemical deoxidation of graphene oxide ( GO ) in films are reported. A difference in mechanism between the photoreduction and thermal reduction of GO has been shown. The mechanism of photochemical deoxidation of graphene oxide has been rationalized using the concepts of molecular photochemistry. A new model of photoelimination of molecular oxygen from epoxy groups on graphene nanosheet has been proposed. The photoprocesses lead to growing of π-domains of graphene.

Photoprocesses in bis(diethylaminobenzylidene)cyclopentanone (D1) and its bis(aza-18-crown-6) derivative (D2) have been studied in acetonitrile. The absorption, fluorescence, and phosphorescence spectra of D1 are similar to those of D2. Laser excitation of oxygen-free solutions of D1 and D2 leads to generation of a triplet state with a lifetime of ∼1 μs and two intermediate species with lifetimes of ∼100 μs and longer than 1 s.

Excitation energies of singlet and triplet pi pi* and n pi* transitions are calculated for chalcone and its aminoderivatives using quantum chemical approach. Solvent impact on the molecular geometry and excited state energies is investigated. Both universal (dipole-dipole) and specific (H-bond formation with C=O group) interactions are taken into account.Dipole-dipole interactions are shown to stabilize the excited S-pi pi* state in the systems studied in the same way as for others heteroaromatic luminophores. Specific interactions in protic solvents cause in addition significant geometry deformation to the non-planar structure of the chromophore. Large intramolecular spin-orbit coupling between the lowest singlet and triplet excited states in the latter case is revealed. It proves that intersystem crossing between these states should be the main channel of fluorescent quenching of 4-(N, N' - dimethylamino)-chalcone in protic solvents. (C) 2015 Elsevier B.V. All rights reserved.

The mechanism of formation of triplet excited states of molecular systems in photonics and radiation chemistry has been considered. Intersystem crossing processes, two-photon excitation of high triplet states, and their evolution are discussed. The specific features of the formation of triplet states in radiation chemistry have been considered. Examples of using the concepts of triplet states in various fields, such as molecular luminescence, photochemistry, radiation chemistry, photodynamic therapy, design of organic light-emitting diodes, and information recording, are presented.