Novel excited state proton transfer reaction observed for proflavine encapsulated in the channels of modified MCM-41

Abstract

Proflavine (3,6-diamino acridine) was encapsulated in mesoporous MCM-41 and in a silane modified MCM-41. Synthesised MCM-41 and modified MCM-41 materials were characterised by XRD, BET, and FT-IR methods. In the dye-encapsulated mesoporous materials the interactions between encapsulated proflavine and the internal surfaces of the porous materials are found to modify the optical spectra and the excited state dynamics of the confined proflavine molecules. In MCM-41 as evidenced by the absorption and emission spectra, proflavine exists in the monocationic form (PFH⁺) with a characteristic absorption maximum at 444 nm. In the silane modified MCM-41, proflavine is found to be present in the neutral form with the characteristic absorption maximum at 394 nm. Steady state fluorescence spectra for all the dye-encapsulated mesoporous materials and lifetimes of the excited state of proflavine encapsulated in these hosts were investigated. Excited state proton transfer reaction is observed for the dye lodged in the nanometer-sized pores of the silane modified MCM-41. A delayed emission in the picosecond time resolved emission decay measurements of the excited state of the dye confirms this process.