Resonance energy transfer study of laser dyes LD 489 and LD 473 with rhodamine 6G

The energy transfer using two laser dyes 6,7,8,9-tetrahydro-6,8,9-trimethyl-4-(trifluoromethyl)-2H-pyrano[2,3-b][1,8] naphthyridin-2-one (LD-489) and 1,2,3,8-tetrahydro-1,2,3,3,8-pentamethyl-5-(trifluoromethyl)-7H-pyrrolo[3,2-g]quinolin-7-one (LD-473) as donors and rhodamine 6G (Rh6G) as acceptor was investigated in methanol using steady state and time resolved fluorescence spectroscopy. The bimolecular quenching rate parameter, k(q), and the translation diffusion rate parameter, k(d), were calculated and these values indicated that the diffusion process alone does not operate in energy transfer process. The mean diffusion length, d(1), is found to be less than the Forster distance, R-O, supporting the dominance of long-range interaction. The critical transfer distances determined from both the Forster equation and the half quenching concentration are close to one another, revealing that the Forster mechanism plays an important role in overall energy transfer of the donors.