PHOTOCHEMISTRY ON SURFACES - SOLVENT MATRIX EFFECT ON THE SWELLING OFCELLULOSE - AN EMISSION AND ABSORPTION STUDY OF ADSORBED AURAMINE-O

Auramine O exhibits a significant fluorescence emission at room temper ature when adsorbed on microcrystalline cellulose. This emission is ab out two to four orders of magnitude higher than the previously reporte d emission in different solvents, also at room temperature. The fluore scence quantum yield, phi(F), varies with the residual degree of humid ity of the sample, as alterations in the rigidity of the environment g reatly affect the non-radiative de-excitation of auramine O. A limitin g upper value of phi(F) almost-equal-to 0.35 was obtained after prolon ged evacuation of the samples. A matrix-isolation mechanism was evalua ted by using room-temperature fluorescence measurements of powdered sa mples of auramine O adsorbed on microcrystalline cellulose. Using pola r protic and aprotic solvents, different degrees of swelling of the mi crocrystalline cellulose were obtained, resulting in changes of the gr ound-state reflectance spectra of auramine O trapped in the natural po lymer chains, as shown by remission function data. The amount of dye a dsorbed or entrapped is reflected in both the fluorescence quantum yie lds and life-times. When auramine O was adsorbed on porous silica, the fluorescence quantum yield was much lower, indicating a higher mobili ty of dye molecules on the silica surface. Oxygen does not affect the room-temperature fluorescence emission of auramine O in silica or in c ellulose.