Luminescence and Geometric and Electronic Structures of Porphyrazines with Annelated 1,4-Diazepine Rings

Absorption, fluorescence, and phosphorescence spectra of metal complexes of 4-tert-butylphenyl-substituted tetra(1,4-diazepino)porphyrazine MPADz 4 Ph 8 ′ (M = Mg, Zn; PA = porphyrazine; Dz = diazepine; Ph = phenyl; Ph′ = 4-tert-butylphenyl) were recorded in DMF at 293 and 77 K. The Q(0–0) absorption bands of MgPADz 4 Ph 8 ′ and ZnPADz 4 Ph 8 ′ did not show signs of splitting, i.e., corresponded to the monomeric form. Singlet–triplet gaps of 4700 cm –1 for the Mg complex and 4800 cm –1 for the Zn complex were determined from fluorescence and phosphorescence spectra. Fluorescence quantum yields and lifetimes were measured. Rate constants of S 1,2 → S 0 radiative transitions and total rate constants of nonradiative deactivation of the S 1,2 states were determined. Internal conversion rate constants were estimated. Conformer geometries of MgPADz 4 Ph 8 (in the 6H tautomeric form) were calculated by density functional theory in the PBE/TZVP version. The conformer of symmetry S 4v (D 2d ) had the lowest energy. Nonplanar diazepine rings induced small but perceptible out-of-plane distortions in the central porphyrazine ring of MgPADz 4 Ph 8 . This feature correlated with the observed Stokes shifts of 400 and 350 cm –1 (at 293 K) for MgPADz 4 Ph 8 ′ and ZnPADz 4 Ph 8 ′ whereas the metal phthalocyanines had shifts of ~50 cm –1 . Excited electronic states of MgPADz 4 Ph 8 were calculated using INDO/Sm. The Q-state energy of 15,200 cm –1 agreed well with the observed value of 14,800 cm –1 . Strong featureless absorption in the range 330–450 nm (Soret band analog) with maxima at ~25,000 and ~29,000 cm –1 was due mainly to two strong electronic transitions with calculated energies of 24,100 and 31,500 cm –1 ; a shoulder on the long-wavelength side of the Soret band at ~23,000 cm –1 , to a transition of calculated energy 23,800 cm –1 .