Solid-state one-way photoisomerisation of Z,E,Z-1,6-(4,4'-diphenyl)hexa-1,3,5-triene dicarboxylate examined using higher-order derivative spectra and powder XRD patterns.
Photochem Photobiol Sci
; 17(3): 271-280, 2018 Mar 14.
Article
em En
| MEDLINE
| ID: mdl-29364307
ABSTRACT
Higher order derivative spectra were applied at first to one-way ZEZ-to-EEE photoisomerisation of dimethyl ester (ZEZ-DPH1) of the titled compound in a methylcyclohexane solution. Many common crossing points emerged in UV-induced derivative-spectral changes to reveal the direct ZEZ-to-EEE photoisomerisation without the transient formation of an intermediate to suggest the bicycle-pedal mechanism. The solid-state photoisomerisation was subsequently monitored by tracing changes in the fourth-order derivatives of absorption spectra of a thin crystalline layer of ZEZ-DPH1 prepared by the drop-casting method, because the distortion of absorption spectra due to light scattering is cancelled. It was suggested that the solid-state photochemical event consists of three steps:
fast ZEZ-to-EEE photoisomerisation, a subsequent slow ZEZ-to-EEE photoisomerisation and very slow disappearance of the EEE-isomer. Studies on powder XRD were also carried out for a drop-cast solid layer of ZEZ-DPH1 to disclose the coexistence of a crystal form other than the original one, and the former exhibited faster ZEZ-to-EEE photoisomerisation when compared with the original crystal form. The results revealed by XRD analysis are in line with those obtained by higher-order derivative spectra, confirming the solid-state one-way photoisomerisation to take place through the bicycle-pedal process.
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MEDLINE
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2018
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Article