To experimentally elucidate conformation dynamics in the excited state, TRIR spectroscopy was performed for 1b in cyclohexane pumped by 267 nm (Figure ). The spectra converged to sharp spectra over 0.74-ps and 2.67-ps timescales, comparable to those observed for 1a. This indicated that the excited-state dynamics were primarily affected by the thienyl diketone core, while the silyl groups had minor effects. The two timescales were attributed to the conformation change and ISC. More importantly, the converged TRIR spectra were consistent with simulated spectra, assuming a TP conformation in the T1 state (Figure ). Thus, both the conformation changes and the ISC were ultrafast, and the RTP is confirmed to originate from the TP conformer.