Confinement‐Driven Photophysics in Hydrazone‐Based Hierarchical Materials

Confinement‐imposed photophysics was probed for novel stimuli‐responsive hydrazone‐based compounds demonstrating a conceptual difference in their behavior within 2D versus 3D porous matrices for the first time. The challenges associated with photoswitch isomerization arising from host interactions with photochromic compounds in 2D scaffolds could be overcome in 3D materials. Solution‐like photoisomerization rate constants were realized for sterically demanding hydrazone derivatives in the solid state through their coordinative immobilization in 3D scaffolds. According to steady‐state and time‐resolved photophysical measurements and theoretical modeling, this approach provides access to hydrazone‐based materials with fast photoisomerization kinetics in the solid state. Fast isomerization of integrated hydrazone derivatives allows for probing and tailoring resonance energy transfer (ET) processes as a function of excitation wavelength, providing a novel pathway for ET modulation. As hibiscus flowers bloom in the morning and close at night, hydrazone derivatives exhibit photoresponsive behavior as a function of an excitation wavelength. While hydrazone “flowers” wilt in the wrong environment, they blossom in a MOF “vase”. Thus, integration of hydrazone‐photoswitches in proper 3D environments cultivates solution‐like photophysical properties in solid‐state materials and allows for modulation of energy transfer processes.