Dependency of the Dimethyldihydropyrene Photochromic Properties on the Number of Pyridinium Electron-Withdrawing Groups |
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Authors: | Elise Lognon Dr Marie-Catherine Heitz Dr Assil Bakkar Dr Saioa Cobo Prof Frédérique Loiseau Prof Eric Saint-Aman Prof Guy Royal Dr Martial Boggio-Pasqua |
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Institution: | 1. LCPQ UMR 5626, CNRS et Université Toulouse III – Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France;2. Univ. Grenoble Alpes, CNRS UMR 5250, DCM, 38000 Grenoble, France |
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Abstract: | Photochromic dimethyldihydropyrenes substituted with electron-withdrawing pyridinium groups have shown an increase of photo-induced ring-opening efficiency and a light sensitivity that is red shifted relative to the unsubstituted compound. However, a recently synthesized tetrapyridinium derivative showed a considerable decrease of the photo-isomerization quantum yield relative to the monopyridinium and bispyridinium derivatives. We provide a rationale for this unexpected photochemical behavior based on the comparative theoretical investigations of the relevant excited states of these systems. In particular, we found that the nature and order of the lowest two excited states depend on the number of pyridinium groups and on the symmetry of the system. While the lowest S1 excited state is photo-active in the monopyridinium and bispyridinium derivatives, the photo-isomerizing state is S2 in the reference unsubstituted compound and both S1 and S2 lead to isomerization in the tetrapyridinium derivative, albeit with a low efficiency. In the latter derivative, the photo-isomerization is hindered by the particular S1/S2 conical intersection topology. |
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Keywords: | computational chemistry conical intersection excited states photochromism photo-isomerization |
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