Triphenylamine substituted dipyrrinato metal complexes: Synthesis, optical and electrochemical studies

A series of triphenylamine substituted dipyrrinato metal complexes (1-8) have been synthesized. The mononuclear type complexes 1-6 have Ni(II), Co(II), Pd(II), In(III), and Zn(II) metal ions in the core. The binuclear type complexes 7 and 8 have Zn(II) metal ion in the center. All the compounds (1-8) were characterized by HRMS, NMR, IR, UV-vis absorption, cyclic voltammetry and fluorescence techniques. The presence of large electron rich triphenylamine moiety at dipyrrin ligands affected the spectral properties of complexes. Except Co(II) complex, other metal complexes exhibited blue shifted absorption maxima in UV-vis studies. The In(III) and Zn(II) metal complexes 4-6 showed red shifted emission maxima in fluorescence compared to their corresponding phenyl analogues. Complexes 3-8 exhibited good Stokes shifts in the range of 4600 to 7000 cm^{- 1} with reduced quantum yields. Singlet state lifetimes of complexes 3-8 were in the range of 2 to 4 ns; also the decrease in radiative decay constants k<inf>r</inf> and the increase in non-radiative decay constants k<inf>nr</inf> were in line with the quantum yield data. CV studies of complexes 1-8 showed anodic shifts in the oxidation potentials, suggesting that meso-triphenylamine group has affected the electronic properties of complexes by making them difficult to oxidize.