The effect of substituent position and solvent on thermal Z‒E isomerization of dihydroquinolylazotetrazole dyes: kinetic, thermodynamic, and spectral approaches

Kinetic and thermodynamic parameters have been investigated for the thermal Z‒E isomerization of dihydroquinolylazotetrazole dyes with alkyl substituents (Me, t -Bu, and Adm) at positions 1 (dyes 2 ) and 2 (dyes 3 ) of the tetrazole moiety in two solvents of different polarity, acetonitrile (MeCN) a...

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Bibliographic Details
Published in:Photochemical & photobiological sciences 2024-01, Vol.23 (1), p.177-187
Main Authors: Golovina, Galina V., Egorov, Anton E., Khodot, Evgenii N., Kostyukov, Alexey A., Timokhina, Elena N., Astakhova, Tatiana Yu, Nekipelova, Tatiana D.
Format: Article
Language:English
Subjects:
Biochemistry
Biomaterials
Chemistry
Chemistry and Materials Science
Original Papers
Physical Chemistry
Plant Sciences
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Summary:Kinetic and thermodynamic parameters have been investigated for the thermal Z‒E isomerization of dihydroquinolylazotetrazole dyes with alkyl substituents (Me, t -Bu, and Adm) at positions 1 (dyes 2 ) and 2 (dyes 3 ) of the tetrazole moiety in two solvents of different polarity, acetonitrile (MeCN) and toluene. The experimental results show crucial dependence of these parameters on a substituent position in the tetrazole moiety and on a solvent. For dyes 2 , E act and Δ H ‡ are lower in MeCN than in toluene that results in a high increase in the lifetimes of the Z isomers: from milliseconds in MeCN to minutes in toluene. For dyes 3 , the difference in E act and Δ H ‡ in the two solvents is opposite: E act and Δ H ‡ are by more than 20 kJ mol −1 higher in MeCN, nevertheless, the rate constants for 3 in toluene are comparable with those in MeCN at the ambient temperature and the difference in the behavior is determined by the value of negative entropy of activation. Quantum-chemical calculations of the thermal Z‒E isomerization show the possibility of the process to occur via crossing from the S 0 to the thermally induced T 1 state. The contribution of this path is highest for 3 in toluene. The analysis of the absorption spectra demonstrates that for the E isomers, the n‒π* and π ‒ π* transitions are within the long-wavelength absorption band and their positions relative each other are opposite in the solvents: the n‒π* transition is blue-shifted relative to the π ‒ π* transition in MeCN and is red-shifted in toluene. Graphical abstract
ISSN:1474-905X
1474-9092
DOI:10.1007/s43630-023-00511-4