The effect of n-type and p-type semiconductors on the photoconversion of colchicine. Experimental and computational study

The effect of n-type (CeO2, SnO2 and TiO2) and p-type (SnO and TiO) semiconductors on the photoconversion of colchicine (COL) was investigated. All investigated semiconductors induced quenching of the fluorescence emission of COL with Stern?Volmer quenching constants , ranging from (1.8 ? 0.1) ? 104 mol?1 ? L for CeO2 to (3.5 ? 0.1) ? 103 mol?1 ? L for TiO2. n-type semiconductors (SnO2 and TiO2) exhibited the most reduction in photo conversion rate constant and yields, achieving ?50% inhibition in the presence of 8?10?5 mol ? L?1 of TiO2 and SnO2. While p-types showed minimal effects. Density functional theory (DFT) calculations were used to provide a clear insight into the effects of semiconductors on Frontier Molecular Orbitals (FMO) structure and HOMO-LUMO energy gaps of COL. DFT calculations showed the presence of n-type semiconductors reduces the HOMO-LUMO energy gap. Moreover, in the presence of n-type semiconductors, changes in the electronic topologies and dihedral angles of phenyl, 7-membered ring and tropolone ring in COL indicate a noticeable involvement of the tropolone and phenyl ?-systems of COL with the conduction band of the semiconductors. These results support the observed fluorescence quenching and reduction of the photoconversion rate of COL in the presence of n-type semiconductors. The combined experimental and computational results elucidate the mechanism underlying fluorescence quenching and photoconversion inhibition, highlighting the crucial role of semiconductor type in modulating COL?s photochemical behavior.