Synthesis of multibranched porphyrins with two-photon absorption and intrarnolecular energy transfer

Three new multibranched porphyrins: 5-(4-nitrobenzoxy)-phenyl-10,15,20-tris-(4-bromophenyl)-porphyrin (TPP-NO2), 5-(4-nitrobenzoxy)-phenyl- 10, 15,20-tris-(4-N,N-diphenylamino-styryl)phenyl-porphyrin (TPP-X-3) and 5,10,15,20-tetra-(4-N,N-diphenylamino-styryl)-phenyl-porphyrin (TPP-X-4) were synthesized and characterized by IR, H-1 NMR and MS measurements, respectively. Pumped by 800 nm and 532 nm laser pulses, respectively, the sample solution could emit strong up- and down-conversion fluorescence, wherein the former cound be interpreted by two-photon absorption (TPA) mechanism and the latter was attributed to two-photon absorption and intramolecular energy transfer. TPA cross-section was measured by femtosecond Z-scan technique at 800 nm Ti : sapphire laser. It was found that TPA cross-section of multibranched porphyrins was enhanced by larger dipole moment difference between the ground- and the excited-state, that is, \Delta mu(ge)\ value, and stronger conjugation effect, that is, pi-pi conjugation, between porphyrin "core" and branches linked to the porphyrin periphery.