Synthesis and photovoltaic properties of new metalloporphyrin-containing polyplatinyne polymers

Three new solution-processable platinum(II) polyyne polymers containing zinc(II) porphyrinate chromophores P1, P2, and P3 and their corresponding dinuclear model complexes were synthesized via the CuI-catalyzed dehydrohalogenation reaction of the platinum(II) chloride precursor and each of the respective bis(ethynyl)-zinc(porphyrin) metalloligands. The thermal, photophysical (absorption, excitation and emission spectra), electrochemical, and photovoltaic properties of P1-P3 were investigated. These results are also correlated by time-dependent density functional theory (TDDFT) calculations. The computations corroborate the presence of moderate conjugation in the π-systems, somewhat more accentuated for P3 where more favorable dihedral angles between the porphyrin and thiophene rings are noted. Moreover, the computed excited states are predicted to be π-π* in nature with some charge transfer components from the trans-[-C≡CPt(L)₂C≡ C-]_n unit to the porphyrin rings. The optical bandgaps range from 1.93 to 2.02 eV for P1-P3. Intense π-π*-localized fluorescence emissions typical of the Q-bands of the polymers were observed. The effect of thiophene ring along the polymer chain on the extent of π-conjugation, luminescent and photovoltaic properties of these metalated materials was also examined. Bulk heterojunction solar cells using these metallopolymers as an electron donor blended with a methanofullerene electron acceptor were studied. In one case, the metallopolymer P3 showed a power conversion efficiency of 1.04% with the open-circuit voltage of 0.77 V, short-circuit current density of 3.42 mA cm^-2 and fill factor of 0.39 under illumination of an AM 1.5 solar cell simulator.