Fabrication and photophysical studies of phenosafranine and proflavine dyes encapsulated in mesoporous MCM-41 along with titanium dioxide nanoparticles

Phenosafranine, PS, (3,7-diamino-5-phenylphenazenium chloride) was encapsulated in mesoporous MCM-41, AlMCM-41 and in a silane modified MCM-41, proflavine, PF, (3,6-diamino acridine) was encapsulated in mesoporous AlMCM-41. Synthesised MCM-41 materials were characterised by SAXRD, surface area measurements, and FT-IR methods. Phenosafranine encapsulated in MCM-41 shows little change in the absorption maxima whereas fluorescence maxima shows a blue shift of 28 nm as compared to that in water revealing a less polar and more hydrophobic nature of MCM-41 channels. Fluorescence lifetime studies show the heterogeneity of the host surface as indicated by the decay curves fitted to biexponential function. Diffuse reflectance laser flash photolysis studies of PS encapsulated in MCM-41 nanocomposites show absorption bands with maxima at around 605, 660 and 700 nm for the transients which are attributed to the protonated form of the triplet excited state (3PSH2+). Photosensitisation of the titanium dioxide nanoparticles encapsulated into the channels of the mesoporous silicates is interpreted to be due to the singlet excited states of the dye molecules and the titanium dioxide nanoparticles in contact with the dye molecules. The mechanism of photosensitization is suggested to be of charge transfer type which occurs at time scale in the sub-pico second domain.