Tetrakis(thiadiazole)porphyrazines. 6. Spectroelectrochemical and Density Functional Theory Studies of the Anions [TTDPzM]n- (n = 1-4; M = ZnII, MgII(H2O), CuII, 2HI )

Following previous cyclic voltammetric studies of tetrakis(thiadiazole)porphyrazines [TTDPzM] where M = ZnII, MgII(H2O), CuII, or 2HI in nonaqueous media, a thin-layer spectroelectrochemical investigation was carried out in pyridine to characterize each stepwise one-electron reduction of the electrogenerated [TTDPzM]n− complexes where n = 1−4. A similar UV−visible spectrum was observed for each form of the anion, independent of the central metal ion and detailed theoretical calculations by density functional theory (DFT) and time-dependent DFT (TDDFT) methods were applied to interpret the spectral features of [TTDPzZn]n− (n = 1−4) which was selected as representative for describing the ground and excited-state electronic structures of the entire [TTDPzM]n− series. The use of two exchange-correlation functionals, the pure, asymptotically correct statistical average of orbital potentials (SAOP) and the hybrid B3LYP functionals, proved to be essential for attaining a correct assignment of the key spectral features. The nature and intensity of the main spectral features are highlighted and interpreted on the basis of the ground-state electronic structure of the complexes.