Abstract
AbstractPiroxicam (PRX), a nonsteroidal anti‐inflammatory drug, exhibits a large Stokes‐shift emission owing to the excited‐state intramolecular proton transfer (ESIPT) from enol‐PRX to keto‐PRX. In contrast, the Cu‐coordinated PRX complex (CuPRX) does not show any emission at 300 K. In the time‐resolved transient absorption (TA) spectra, PRX showed two positive TA bands at 430 and 700 nm, corresponding to the S1–Sn transitions of keto‐PRX* and a negative bleaching band at 540 nm due to ESIPT emission. These TA bands decayed with a lifetime of approximately 50 ps. CuPRX showed similar TA features, but no bleaching band was observed for CuPRX and decayed rapidly within 3 ps, indicating a rapid intersystem crossing process owing to the heavy atom effect. Based on the experimental results and theoretical calculations, the fate for excited keto‐PRX is discussed in terms of the ESIPT and reverse ESIPT processes.
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