Photochromic resorcin[4]arenes: stabilization of intramolecular anthracene dimers in solution.

Several resorcin[4]arenes functionalized with two anthracene units on opposite sides of the upper rim of the macrocycle were synthesized. We investigated the potentially photochromic properties of these systems, with the main focus on the intramolecular [4+4] cycloaddition of the anthracenes and its reversibility by thermal ring opening. Whereas compound 9 proved to be a switchable host system (by irradiation and temperature, T-type photochromic substances), compounds 10-12 formed intramolecular photodimers upon irradiation, which are only stable at low temperature. The reopening occurred immediately at room temperature and was followed by UV/VIS spectroscopy. Further investigations showed that the cyclodimer of 11 can be stabilized significantly by sodium cations due to crown ether-like complexation. Additionally, quantum chemical calculations were performed to evaluate the different behaviour.