Aryl imidazoisoindoles for intrinsic 10π pericyclic photochromism with nonlinear acid responsiveness

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Abstract
Photochemical and thermal peri-cyclization and cycloreversion reactions of organic polyenes are typically governed by orbital symmetry considerations. Here, we report two aryl-imidazoisoindole derivatives featuring benzene and thiophene rings that undergo reversible photochromic reactions via 10π cyclization and cycloreversion. The synthetic study was fully characterized using NMR, mass spectroscopy, and X-ray analyses, which are further supported by quantum chemical calculations based on density functional theory (DFT). Both molecules exhibit a reversible color change under UV and visible light irradiation. Photochemical quantum yields are presented, showing suppression with solvent polarity. The colored ring-closed form displayed a spontaneous fading reaction, whose thermodynamic parameters are well characterized. The thiophene-based substance exhibited a lifetime of 67 h, which was markedly reduced upon protonation of the imidazole ring. Notably, small amounts of acid markedly enhanced the spontaneous fading reaction through a catalytic mechanism. DFT calculations clearly supported the ground-state structures and the major contribution of the neutral mesomeric form in both substances. The reaction pathway and transition state for the thermal reaction were also characterized, which rationally support the major contribution of reversible 10π-photocyclization/cycloreversion reactions.
Funding Information
  • Ministry of Education, Culture, Sports, Science and Technology (JPMXP1224NR5023)
  • Institute for Molecular Science (JPMXP1223MS0021)
  • Institute for Molecular Science (JPMXP1224MS0035)
  • Japan Society for the Promotion of Science (JP23H04876)
  • Japan Society for the Promotion of Science (JSPS KAKENHI Grant-in-Aid for Transformative Research Areas, Materials Science of Meso-Hierarchy)

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