V. G. Plotnikov

The graphite oxide photoreduction mechanism

The mechanisms of dissociation of oxygen-containing moieties (-OH, -HCO, -COOH) upon the photoreduction of graphite oxide by UV light have been considered. It has been concluded that the photoreduction, which involves the detachment of the OH group and the molecular elimination of CO and CO2, occurs in singlet excited states. The energy threshold of the photoreduction processes is determined by the position of the repulsive terms of the system.

Experimental and Theoretical Investigation of the Spectral and Luminescent Properties of Some Acridine Compounds

Complex (experimental and quantum-chemical) investigation of the spectral and luminescent properties of acridine, 9-aminoacridine, 2,7-dimethyl-9-ditolylaminoacridine, and their protonated forms was performed. The electronic absorption and fluorescence spectra of the acridine dyes were studied at room temperature in ethanolic solutions at different pH values and in other solvents of different chemical nature and polarity. The energies of the excited states, the deactivation rate constants for the excited states, and the dipole moments are presented, which were obtained by calculations using the method of intermediate neglect of the differential overlap with special spectroscopic parameterization.

Intermolecular interactions and spectral and luminescent properties of optical molecular sensors

The effect of intermolecular interactions of different types (universal interactions, H-bonding, electronic donor-acceptor interactions, and interactions with proton transfer) on the absorption and luminescence spectra of organic molecules of different classes, which are or can be used as optical molecular sensors, was considered. The classification of the types of intermolecular interactions and corresponding spectroscopic effects is given, which can be used, particular, in the development of optical sensors for detection of organic molecules in liquid and gaseous media.

Photophysical Processes and the Photodissociation of Chemical Bonds in Polyatomic Molecules

The main concepts of the nature of electronically excited states in polyatomic molecules and the intramolecular and intermolecular processes of their evolution are reported. The dependence of the probabilities of these processes on the electronic structure of the molecule is considered. Possible mechanisms of the dissociation of electronically excited molecules with bond cleavage are discussed, and the theoretical results of this consideration are given. The experimental data obtained by the authors are interpreted. In this case, attention is focused on C-H-bond photodissociation processes in a condensed phase, which are the best studied processes. The dissociation of other bonds is briefly discussed.

Two-photon photoprocesses in molecular systems

A review of two-photon photoprocesses of polyatomic molecules in the condensed phase is presented. The mechanism and the kinetics of absorption of the second photon of light are discussed, as well as the features of the main two-photon processes (ionization, electronic excitation energy transfer, dissociation with abstraction of hydrogen atoms and molecular products). The research capabilities of the method are demonstrated. It is emphasized that one of the main requirements to molecules of effective light stabilizers for polymers is the absence of two-photon processes for these molecules, which is provided by the nonradiative conversion processes initiated by reversible adiabatic reactions. On this basis, interpretation of the properties of the main classes of light stabilizers for polymers is given.

Photonics of bis(diethylaminobenzylidene)cyclopentanone and its analogue with the bisazacrown moiety in acetonitrile

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.

Triplet states of 3,3′-alkylsubstituted thiacarbocyanine dimers and dimeric complexes with cucurbit[8]uril in water

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.

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone and its bis(aza-18-crown-6)-containing analogue in acetonitrile

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-Tmax = 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.

Photochemical processes in graphene oxide films

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.

Exciplexes in highly excited triplet states

A mechanism of energy transfer from highly excited triplet aromatic molecules has been developed, which involves a stage of formation of an exciplex between a highly excited energy-donor molecule and an unexcited energy-acceptor molecule. Interpretation of the experimental data on the shape and the intensity of triplet-triplet absorption bands and the energy transfer probability is presented. In this interpretation, the results of quantum-chemical calculations of the energies of highly excited triplet states of toluene and benzene molecules are used.