Tuning Solid-State Switching of the First Dihydroazulene@MOF Hybrid Materials

Solid-state switching of photo- and thermochromic dye molecules like dihydroazulene (DHA) is drastically reduced due to steric demands compared to that of solutions. In this work, we present the first DHA–metal–organic framework (MOF) hybrid approach, utilizing MOFs of varying polarities as host matrices for DHA. The resulting DHA@MOF systems exhibit a T-type photochromism upon light irradiation, which is strongly dependent on the host matrix used. Further, changes in the vibrational modes during the switching process were traced via IR spectroscopy under ambient conditions, which are in accordance with the results obtained from quantum chemical calculations. Here, the optical properties were directly related to the MOF pore confinement. This fundamental insight into the optical response of a T-type chromophore within a porous host scaffold will further soften boundaries in basic applied sciences to push the systematic design of functional materials.