Effect of natural and modified cyclodextrins on the excited state proton transfer of 7-hydroxy-4-methylcoumarin

Abstract Effect of natural and modified cyclodextrins on the absorption and 2D, 3D fluorescence spectra of 7‑hydroxy‑4‑methyl coumarin (HMC) have been investigated in different buffer solutions (pHs – 1.0, 6.5 and 10.0). Both neutral and monoanion species were formed in the ground state, whereas three species such as zwitterion, neutral and monoanion in the excited state in the above mentioned pH ranges. The excited state property of HMC obviously varied with the results from the absorption data. The excited state proton transfer was observed at low pH from the hydroxyl group to carbonyl group of HMC. FT-IR, PXRD, SEM results showed the apparent variation in the natural and modified CDs with the HMC molecule. The results demonstrated that in three pH solutions, HMC forms 1:1 inclusion complex with the three CDs. Finally the proposed structures of the inclusion complexes were predicted using Semi-empirical calculations.