The synthesis and characterization of photonic materials composed of substituted fluorene donors and a porphyrin acceptor

Three novel porphyrin derivatives namely 5,10,15,20-tetra-[7-cyanophenyl-9,9’-bis-(2-ethylhexyl)fluoren-2-yl]-porphyrin, 5,10,15,20-tetra-[7-(4-acetylphenyl)-9,9’-bis-(2-ethylhexyl)fluoren-2-yl]-porphyrin and 5,10,15,20-tetra-[7-pyrenyl-9,9’-bis-(2-ethylhexyl)fluoren-2-yl]-porphyrin were synthesized. Substitution of the aryl groups on the meso-fluorene using Suzuki-Miyaura coupling enabled a study to be undertaken of the energy transfer from the meso fluorenyl to the porphyrin core. To calculate the extent of energy transfer, the corresponding model fluorene compounds 7-cyanophenyl-9,9’-bis-(2-ethylhexyl)fluorene, 7-acetylphenyl-9,9’-bis-(2-ethylhexyl)fluorene and 7-pyrenyl-9,9’-bis-(2-ethylhexyl)fluorene were also synthesized. Fluorescence studies of both the porphyrin derivatives and model compounds showed efficient energy transfer occured from the aryl-fluorene donor to the porphyrin acceptor. Upon excitation, due to energy transfer, a characteristic porphyrin emission was observed at ∼656 nm; ∼99% energy transfer in solution was observed in these donor–acceptor systems. Thin-film emission results indicate a low degree of aggregation in the donor–acceptor systems.