Boosting Ultrafast Trans-Cis Photoisomerization and Intersystem Crossing in Nanocrystals of Double-Bond Photoswitching Molecules

摘要

Double-bond photoswitching molecules typically can undergo trans→cisphotoisomerization, but their photoisomerization mechanisms in the solidstate have been rarely reported. Herein, the excited-state evolutions oftrans-azobenzene (AB), trans-stilbene (TS), and N-benzylideneaniline (NBA)are studied to unveil the relationship between the double-bondphotoswitching molecules and the photoisomerization kinetics in the solutionphase and in nanocrystal suspensions (NCS). The photoisomerization rate ofNBA is the fastest among these three molecules in the solution phase due toits most apparent single-bond feature of the central double bond in the S_1state. The free space ordered crystal configuration boosts thephotoisomerization rates of AB and TS in NCS to be faster than that of thesolution phase because the hindrance of the wrapping solvent is eliminated inthe crystals. In contrast, when NBA is prepared into NCS, it becomesdistorted into a nonplanar structure because of the asymmetrical C-H··· interactions, resulting in NBA having a large spin-orbital coupling (SOC) valuewhich opens the intersystem crossing channel to generate the triplet stateinstead of undergoing photoisomerization in solution. Therefore, this workreveals that the crystal configuration and the molecular structure maycritically determine the photophysical properties of photoswitching materials.