Morphology-dependent exciton emission and energy transfer in fluorene-polymer-related fluorescent and phosphorescent composite films spin cast from a mixture of two dissimilar organic solvents

We report morphology-dependent exciton emission and energy transfer in fluorene-conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl)-related fluorescent and phosphorescent materials by using a mixture of two dissimilar organic solvents for spin-cast film formation. The electron microscopic characterizations revealed that the mixture of a high-boiling-point orthodichlorobenzene and a low-boiling-point chloroform results in a formation of both crystalline and amorphous morphological structures in fluorene-conjugated polymers. The UV-visible absorption and photoluminescence studies indicated that the low-energy crystalline phase domains, randomly distributed in the continuous high-energy amorphous phase, function as potential quantum wells. As a consequence, the mixture of two dissimilar organic solvents significantly affects the exciton emission from fluorescent fluorene-conjugated polymer and the energy transfer in phosphorescent composite of fluorene polymer and iridium complex molecules, presenting a pathway to control fluorescent and phosphorescent processes in polymer light-emitting materials.