박상황 (POSTECH)

서종철 (POSTECH)

박상황 (POSTECH)

서종철 (POSTECH)

Diarylethene (DAE) is a molecule well-known for its photochromic photoisomerization properties. DAE undergoes reversible ring opening and closing in response to light, typically closing upon exposure to UV light and opening under visible light. In this study, we investigated the photoisomerization of DAE using ion mobility spectrometry-mass spectrometry (IMS-MS). Specifically, we utilized 2,3-bis(2,4,5-trimethyl-3-thienyl)maleimide (DAE-C0) as the DAE molecule. A hand-held UV lamp served as the UV light source, while white light was used as the visible light source. Two main experimental approaches were employed: 1) Offline irradiation: DAE-C0 was irradiated with light and then analyzed using IMS-MS. 2) Online irradiation: DAE-C0 was exposed to light during the ESI process for real-time IMS-MS analysis. The IMS-MS results revealed distinct arrival time distributions (ATD) for the open-ring isomer (O-DAE-C0) and the closed-ring isomer (C-DAE-C0). The data suggest the potential existence of an intermediate structure between O-DAE-C0 and C-DAE-C0. Additionally, the effect of solvent conditions on isomerization was investigated. Under THF solvent conditions, O-DAE-C0 and C-DAE-C0 underwent efficient isomerization in response to light exposure. In contrast, in the protic solvent MeOH, photoisomerization was significantly less pronounced. These observations were consistently supported by both IMS-MS and UV-Vis absorption spectroscopy data. In conclusion, this study demonstrates the utility of IMS-MS in distinguishing between the open- and closed-ring isomers of DAE under various light and solvent conditions. The findings suggest the sensitivity of the photoisomerization process to solvent environment, with protic solvents like MeOH inhibiting isomerization compared to aprotic solvents like THF. These insights not only enhance our understanding of the photochromic behavior of DAE molecules but also suggest potential applications in designing responsive materials and devices based on controlled photoisomerization.