Synthesis, Photophysical Properties and Computational Studies of beta-Substituted Porphyrin Dyads

Beta-pyrrole-substituted porphyrin dyads connected by ethynyl linkage to N-butylcarbazole or triphenylamine donors are reported. Donor-π-acceptor type beta-substituted porphyrin dyads and their Zn(II) and Pd(II) complexes were characterized by MALDI-MS, NMR, UV-vis absorption, fluorescence and cyclic voltammetry techniques. The S₁ emission dynamics were analyzed by time-resolved spectroscopy (TCSPC); dyads exhibited efficient energy transfer up to 93% from beta-donors (N-butylcarbazole or triphenylamine group) to the porphyrin core. The efficiency of energy transfer for the beta-substituted porphyrin dyads were much higher than those of the corresponding meso-substituted porphyrin dyads, reflecting enhanced communications between the beta-donors and the porphyrin core. The Pd(II) dyads, showed characteristic phosphorescence in the near IR region and very efficient singlet oxygen quantum yields (53–60%); these dyads are promising candidates for photocatalytic oxidations of organic compounds. The donor-acceptor interaction between the porphyrin core and the beta-donors was supported by the DFT studies in the porphyrin dyads.