최동진 (포항공대 화학과)

서종철 (포항공대 화학과)

최동진 (포항공대 화학과)

박상황 (포항공대 화학과)

서종철 (포항공대 화학과)

Musleh Uddin Munshi (포항공대 화학과)

2,3-Bis(2,4,5-trimethyl-3-thienyl)maleimide (BTTM) is a photochromic organic compound that exhibits reversible photoisomerization between its open and closed forms upon irradiation with UV and visible light. UV–Vis spectroscopy reveals a pronounced color transition from yellow to red under UV irradiation, followed by recovery of the original yellow color under visible-light irradiation. These spectral changes confirm the reversible conversion between the two photoisomers. However, UV–Vis spectroscopy yields only an ensemble-averaged response and cannot directly determine the relative populations of individual photoisomers. Gas-phase ion mobility–mass spectrometry (IM–MS), in contrast, separates ions according to their structure-dependent mobilities and allows the distributions of distinct isomeric species to be determined. In this study, we show that IM–MS resolves the BTTM photoisomers and permits quantitative analysis of their relative populations. Density functional theory (DFT) calculations further identify several possible protonation sites and suggest that protomers with lower interconversion barriers exhibit broader arrival time distribution (ATD) peaks. Structural assignments of the photoisomers and protomers were established through comparison of experimentally measured collision cross section (CCS) values with those predicted by DFT calculations. Future studies will employ gas-phase infrared spectroscopy to provide complementary structural characterization of both photoisomers and protomers. Overall, this approach provides an effective analytical platform for the separation and structural characterization of photoisomeric and protomeric species and offers further insight into the photoisomerization mechanism of BTTM.

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