I. I. Dilung

Dipole moments of exciplexes of heteroaromatic compounds with N, N-dimethylaniline

The influence of the polarity of a solvent on the position of the maximum of the fluorescence band of exciplexes of N, N-dimethylaniline (DMA) with exctied molecules of phenazine, acridine, and their benzo-, dibenzo- and tetrabenzo derivatives was studied. From the regularities found, the Μ2/γ3h values were evaluated, giving an estimate of the dipole moments of the exciplexes under consideration. An attempt was made to find a correlation between Μ2/ϱ3h values and the value of the enthalpy of formation δH of the corresponding excited complexes. It was concluded that for the first members of the azine series, the Μ2/ρ3h value does not reflect the degree of charge transfer in the exciplex, and cannot be correlated with AH. Explanations are presented which give as the main reason for this lack of correlation the possible conformational changes undergone by the excited molecules of azines during the formation of the exciplexes.

Generation of radical particles in the excited complexes of polynuclear aromatic compounds with acrylic monomers

The existence of ternary excited complexes of the electron-acceptor type was confirmed by quenching the fluorescence of the exciplexes of polynuclear aromatic compounds with N,N-dimethylaniline by additions of butyl methacrylate. It is suggested that when photoinitiator-N,N-dimethylaniline-monomer systems is increased the ternary complex is transformed into an ion triplet, which is situated in a solvent cage, and that the ion triplets participate in the initiation of the polymerization of butyl methacrylate.

Effect of the electronic structure of heteroaromatic compounds on their phototransformations in polar media

The effect of the electronic structure of aromatic (anthracene) and heteroaromatic (phenazine, acridine, 9-methyl-1,2-benzacridine) compounds on the mechanism of the formation of exciplexes with N,N′-dimethylaniline and their further transformations in media with various polarities was investigated by the quenching of the fluorescence of the exciplex. It was shown that for heteroaromatic compounds characterized by a substantial contribution from the nπ* electronic configuration to the lowest excited singlet state, in contrast to aromatic compounds, the exciplex is formed in two stages, i.e., nonequilibrium Franck-Condon and equilibrium stages. The photodissociation processes for these systems in polar media also take place from a non-equilibrium state. The important role of the steric configuration of the components of the exciplex in its relaxation process was also noticed.

Participation of exciplexes in the photochemical reactions of trinuclear aromatic compounds with N,N′-dimethylaniline in solutions with various polarity

Characteristics of the photoreduction of trinuclear aromatic compounds (phenazine, acridine, and anthracene) by N,N-dimethylaniline (DMA) in media with various polarity (benzene and benzonitrile) were investigated. On the basis of the obtained relationships between the reciprocals of the quantum yields of photoreduction and the reciprocals of the DMA concentration and also on the basis of experiments with biacetyl it was established that the photoreduction is realized with the participation of the lowest excited S1 and T1 states. It was shown that the photochemical reduction of the trinuclear aromatic compounds takes place by a mechanism involving an exciplex.

Electron transfer reaction in the initiation of polymerization of butyl methacrylate in solution

The dilatometric method was used in establishing that in acetonitrile the rate of photopolymerization of butyl methacrylate (λex = 366 nm) initiated by phenazine, acridine, or anthracene in combination with N,N′-dimethylaniline is 1–1.5 orders higher than in benzene. The fluorescence damping and pulsed photoexcitation methods were used to show that in acetonitrile solvate-separated ion radicals form owing to the photodissociation of exciplexes of photoactive compounds with DMA. It is proposed that these ion radicals are primary active products that initiate the polymerization chain in acetonitrile. Initiation of polymerization in benzene is accomplished by a free-radical mechanism. The formation of ternary excited complexes with the monomer and their role in initiation are discussed.

Effect of the orbital nature of the excited state on the reactivity of phenazine compounds

A relationship was established between the nature of the lowest electronically excited singlet state (nπ* or ππ* configuration) and reactivity in the formation of exciplexes with N,N-dimethylaniline as an electron donor on the basis of a study of the spectroluminescent properties of phenazine and its benz, dibenz, and tetrabenz derivatives. The reactivity was found to depend on the energy, type of electronic transition, and structure of the complexes formed. Hypotheses are presented concerning the participation of the second excited state in the reaction.

Role of the vibrational coupling of 3nπ* and 3ππ* states in reactions resulting in the formation of triplet exciplexes of phenazine compounds with dimethylaniline

The relationship between the nature of the reactive triplet state of phenazine, as well as its mono-, di-, and tetrabenzo derivatives, and their reactivity in the formation of triplet exciplexes with amines has been investigated. It has been shown that the reactivity of triplet excited states of phenazines is determined mainly by the presence of vibrational mixing of the lower T1 and T2 triplet states with different electronic configurations (of the nπ* or ππ* type) and the position of the T2 level. The total reaction rate is determined by the sum of the rates of the processes with the participation of the T1 and T2 states.

Reaction of excited aminophenazine molecules with alcohols

I t Was shown e a r l i e r that exci ted me thoxy, ace ty l , and aminophenazine molecu les a r e capable of r e a c t in4~ with va r ious e lec t ron donors and a c c e p t o r s , fo rming exciplexes [1, 2]. T h e i r fo rma t ion is accompanied by a sharp change in the f luo rescence quantum yield of the init ial f luorophor . An equation was der ived in [3], desc r ib ing the obse rved changes in f luo rescence quantum yield of phenazine compound on the concentra t ion of added e lec t ron donor or accep to r . However , it should be cons idered that this equat ion holds t rue only fo r such s y s t e m s in which the introduced addi t ives do not tend to s e l f a s s o c i a t e and cannot be used fo r s y s t e m s where the addit ives f o r m aggrega te s with each o ther .