Direct Spectroscopic Evidence of Photoisomerization in para-Methoxy Methylcinnamate Revealed by Low-Temperature Matrix-Isolation FTIR Spectroscopy.

The photoisomerization of para-methoxy methylcinnamate (p-MMC) has been studied by low-temperature matrix-isolation FTIR spectroscopy. In particular, the difference spectrum of the mid-IR frequency region (1100-1800 cm(-1)) allows us to distinguish the structural change before and after ultraviolet (UV) light irradiation at ≥300 nm and to convince that the cis-isomer is produced from the trans-isomer by comparing with the calculated IR spectra. Additionally, a reversible isomerization of p-MMC is demonstrated upon a sequential irradiation with different wavelengths of UV light. These findings provide a new insight into the electronic excited-state dynamics of p-MMC.