Synthesis of meso-coumarin-substituted porphyrins

Three novel meso-coumarin-substituted porphyrins 3a, 3b and 3c have been synthesized via the reduction of the corresponding porphyrin-counmarin Schiff bases 2a, 2b and 2c, which were obtained by condensation of coumarin aldehydes with 5-(4-aminophenyl)-10, 15, 20-triphenylporphyrin in refluxing toluene. The three novel porphyrins were characterized by 1 H-NMR, HR-ESI, UV-vis and fluorescence spectra. Analysis of the fluorescence spectra indicate that there is energy transferring between the coumarin substituents and the porphyrin core in the excited states of the molecules. For porphyrin 3b in which there is an electron-donating methoxy substituent present on the coumarin ring, the energy is transfered from coumarin substituents to the porphyrin core. However for 3a or 3c, which contains a benzo-coumarin unit (3a) or a methyl substituted coumarin ring (3c), the energy is transfered from the porphyrin core to coumarin substituents.