Spectroscopic studies on the excited-state properties of the light-induced antiviral drug hypocrellin A loaded in the mesoporous solid

Hypocrellin A (HA) is encapsulated in the mesoporous material MCM-41 for the first time, and its excited-state behaviors are elucidated by means of steady-state spectroscopies and excited-state lifetime measurements. No ground-state tautomer of HA in the mesoporous solid is deduced based on the spectra observed. Normal fluorescence energy level results from the (l, aπ) state with pπ conjugation; the excited-state intramolecular proton transfer (ESIPT) fluorescence is mostly due to the two-photon excitation (or absorption) of HA. The ESIPT emission intensity becomes truly remarkable with increasing excitation laser intensities. The time-resolved fluorescence measurements are also performed as the further evidence.