Olga D. Laukhina

Evidence for an adiabatic reaction pathway for trans-to-cis photoisomerization of di(α-naphthyl)ethylene

Abstract Direct photocyclization of trans-di(α-naphthyl)ethylene to dihydropicene with a quantum yield of 0.03 was observed. The kinetics of the photochemical transformations and the effect of the excitation intensity on the yield of dihydropicene was studied. A novel adiabatic reaction pathway for trans-to-cis photoisomerization of di(α-naphthyl)ethylene was suggested.

Spectral and photochemical properties of bifunctional compounds and their complexes

Quantum yields of the step-by-step photocyclization of diphenylamine (DPA) derivatives Ph2N−(CH2)n−NPh2,n=3–6, 9, to the corresponding α,ω-di(carbazolyl)alkanes were measured. Atn>3, the presence of the second DPA group had no effect on the cyclization of the first DPA group; however, cyclization of the second DPA group was retarded after cyclization of the first DPA group. The effect was explained by quenching of the excited DPA group by the carbazole group newly formed in the semi-cyclic compound. For disubstituted propane (n=3), the mutual influence of the two groups at both stages of the reaction was found.

Bimolecular cyclization of di-p-tolylamine to 2,7-dimethylacridine in the presence of bromoform: microsecond flash photolysis study

Abstract The UV irradiation of di- p -tolylamine and bromoform results in the formation of 2,7-dimethylacridine (with a quantum yield of 0.20 ± 0.04). The primary transient spectrum (λ max ≈ 700 nm), recorded following microsecond flash lamp excitation, can be attributed to the amine cation radical and, probably, the neutral diarylnitrogen radical, which arises from the former on deprotonation. Both of these radicals can recombine with the dibromomethyl radical to give the intermediate IM1. This is transparent in the visible region of the spectrum and is transformed into the second intermediate IM2 (λ max ≈ 540 nm), which finally gives rise to acridine. The observed first-order rate constant of IM2 formation is dependent on amine concentration, indicating the participation of an additional amine molecule in the transformation of IM1 to IM2. A new reaction scheme is proposed which assumes that the attack of the alkyl radical is predominantly directed towards the nitrogen atom of the amine radical.

Effect of silver ions on the photochemical properties of N-methyldiphenylamine

Abstract Silver(I) ions have been found to quench the fluorescence of N-methyldiphenylamine (1) and reduce the quantum yield of cyclization reaction of 1 to N-methylcarbazole (3). Comparison of relative quenching rate constants for the singlet- and triplet-excited states of 1 has enabled the evaluation of two components, physical and chemical, in silver(I) action on the triplet-excited 1 ( 3 1 ), namely: acceleration of the intersystem crossing processes 3 1 → 1 and inhibition of the reaction of 3 1 photocyclization to the triplet-excited N-methyldihydrocarbazole (2).

Spectral and photochemical properties of bifunctional compounds and their charge-transfer complexes. Derivatives of diphenylamine

Spectral properties of diphenylamine (DPA) derivatives Ph2N-(CH2)n-NPh2 (n = 1, 3, 5, and 9) and their charge-transfer complexes with CBr4 have been studied. The interaction of two Ph2N groups results in hypsochromic shifts of absorption bands and changes in their intensities in spectra of diamines whenn = 1 and 3 compared to the spectra ofN-alkyl-substituted derivatives of DPA. The spectrum of the diamine complex whenn = 1 is shifted hypsochromically, while those of the other diamine complexes are shifted bathochromically relative to the spectrum of theN-methyldiphenylamine complex. The positions of absorption maxima in the spectra correlates with the values of redox potentials of amines. Irradiation at the charge-transfer band (λ ≈ 365 nm) of complexes between diamines and CBr4 results in the formation of dyes, which absorb at 550 to 700 nm and presumably have di- and triphenylmethane structures.

Photochemical reaction oftrans-di(α-naphthyl)ethylene with diphenylamine

Diphenylamine adds to the ethylene bond of excitedtrans-di(α-naphthyl)ethylene (1). Dependence of the quantum yields of mono- and bi-molecular reactions of1,cis-di(α-naphthyl)ethylene2, and dihydropicene3 on amine concentration was studied. On this basis and theoretical analysis of the kinetic scheme a conclusion was drawn that amine interacts with excited1 with a diffusion-limited rate but has no effect on the photochemical activity of2 and3. The reaction mechanism was discussed.

Intermediates in the photochemical reaction for the formation of 2,7-dimethylacridine from ditolylamine and bromoform

The reaction of the photochemical synthesis of 2,7-dimethylacridine from di(para-tolyl)amine and bromoform was studied utilizing the method of microsecond impulse photolysis. The proposed new scheme for the formation of acridine assumes the recombination of the primary alkyl radicals at the nitrogen atom of the cation radical and/or the radical of the amine as the main route of the reaction. The data obtained indicate the common character of the nature of some intermediate stages and the structures of the intermediates in the photochemical formation of acridine compounds and triphenylmethane dyes from aromatic amines and halogenomethanes.

Study of the thermal stages of the photoinitiated cyclization of diarylamines with polyhalogenated methanes

On the basis of a study of the kinetics of the dark stages of the photoinitiated formation of acridines from substituted diphenylamines and bromoform the ionic nature of these stages was confirmed. Quantum chemical calculations confirmed the assumption of the dependence of the efficiency of cyclization on the charge state of the reacting molecules.