Molecular forms of coumarin-307 in sol-gel glasses.

Coumarin-307(C-307) impregnated sol-gel glass samples were prepared by two methods - (I) predoping using HNO3 as catalyst, and (II) postdoping using HNO3 as catalyst and formamide as drying control chemical additive (DCCA). The absorption/fluorescence properties including fluorescence lifetime of the dye in these sol-gel host matrices were studied and results were compared with dye in methanol (MeOH). In addition to usual non-polar form of C-307 that exists in MeOH, amino-protonated form and dimer of dye have also been found to co-exist in the dried state of samples prepared by predoping method. This behaviour of dye was uncommon to sol and gel states of materials. The fluorescence quantum yield (Qf) of C-307 doped solid was found to be 0.77 and it was almost constant in the concentration range 5 x 10(16) to 8.8 x 10(17) cm(-3). On the other hand, only non-polar form of C-307 has been observed in the samples prepared by postdoping method. The Qf value of dye was 0.96 in the postdoped samples. To explain such behaviour of C-307 in the two types of sol-gel matrices: dye concentration, role of HNO3, water, formamide and matrix effect have been taken into account.