Light-induced cooperative electron-proton transfer in hydrogen-bonded networks of N,N-diaryl substituted 1,4-bisimines and meso-1,2-diaryl-1,2-ethanediols.
The 1:1 cocrystn. of 1,4-diaryl-1,4-bisimines (R-CH:N-CH2-)2 (R = aryl) and substituted meso-1,2-diaryl-1,2-ethanediols leads to supramol. structures in which the diol is H-bonded by 1 of its OH groups to an imine N atom of a 1,4-bisimine. The 2nd functionality in each mol. leads to the generation of ladderlike polymeric structures where each mol. of the diol is linked to 2 mols. of the 1,4-bisimine and vice versa. If the diol carries electron donor groups in the arom. residue and the 1,4-bisimine correspondingly acceptor groups, then charge transfer interactions are obsd. The excited CT complex which corresponds to a radical ion pair is stabilized by migration of a proton of a OH group to the N atom of an NH group. This is supported by the appearance of a N-H vibration in the IR spectra. The reorganization is also accompanied by changes in the UV/Vis spectra and by the generation of paramagnetism in the cryst. material. The results represent a type of photochromism which has its origin in a light-induced cooperative electron-proton transfer. The photochromism is thermally reversible.
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