2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato zinc(II) (3) and 2,3,9,10,16,17,23·24-octakis-(3,6-di-tert-butyl-9H-carbazole) phthalocyaninato zinc(II) (4) complexes were prepared and characterized by NMR and UV-vis spectroscopies, magnetic circular dichroism (MCD), matrix-assisted laser desorption ionization mass spectrometry, and X-ray crystallography. UV-vis and MCD data are indicative of the interligand charge-transfer nature of the broad band observed in 450-500 nm range for 3 and 4. The redox properties of 3 and 4 were probed by electrochemical and spectro-electrochemical methods, which are suggestive of phthalocyanine-centered first oxidation and reduction processes. Photophysics of 3 and 4 were investigated by steady-state fluorescence and time-resolved transient absorption spectroscopy demonstrating the influence of the carbazole substituents on deactivation from the first excited state in 3 and 4. Protonation of the meso-nitrogen atoms in 3 results in much faster deactivation kinetics from the first excited state. Spectroscopic data were correlated with density functional theory (DFT) and time-dependent DFT calculations on 3 and 4.

It is well‐known that treatment of β‐octaethylporphyrin with H2O2/conc. H2SO4 converts it to a β‐oxochlorin as well as all five constitutional isomers of the corresponding β,β’‐dioxo‐derivatives: two bacteriochlorin‐type isomers (β‐oxo groups at opposite pyrrolic building blocks) and three isobacteriochlorin‐type isomers (β‐oxo‐groups at adjacent pyrrolic building blocks). By virtue of the presence of the strongly electronically coupled β‐oxo auxochromes, none of the chromophores are archetypical chlorins, bacteriochlorins, or isobacteriochlorins. Here the authors present, inter alia, the single crystal X‐ray structures of all free‐base diketone isomers and a comparative description of their UV‐vis absorption spectra in neutral and acidic solutions, and fluorescence emission and singlet oxygen photosensitization properties, Magnetic Circular Dichroism (MCD) spectra, and singlet excited state lifetimes. DFT computations uncover underlying tautomeric equilibria and electronic interactions controlling their electronic properties, adding to the understanding of porphyrinoids carrying β‐oxo functionalities. This comparative study lays the basis for their further study and utilization.

An insight into the electronic structure of the metal-free, unsubstituted, and nonperipherally substituted with electron-donating groups tetraazaporphyrin (H2TAP), phthalocyanine (H2Pc), naphthalocyanine (H2Nc), anthracocyanine (H2Ac) platforms has been gained and discussed on the basis of experimental UV–vis and MCD spectra as well as density functional theory (DFT), time-dependent DFT (TDDFT), and semiempirical ZINDO/S calculations. Experimental data are suggestive of potential crossover behavior between the 1 1B2u and 1 1B3u excited states (in traditional D2h notation) around 800 nm. A large array of exchange-correlation functionals were tested to predict the vertical excitation energies in H2TAPs, H2Pcs, H2Ncs, and H2Acs both in gas phase and solution. In general, TDDFT-predicted energies of the Q x and Q y bands and the splitting between them correlate well with the amount of Hartree–Fock exchange present in a specific exchange-correlation functional with the long-range corrected LC-BP86 and LC-wPBE functionals providing the best agreement between theory and experiment. The pure GGA (BP86) exchange-correlation functional significantly underestimated, while long-range corrected LC-BP86 and LC-wPBE exchange-correlation functionals and semiempirical ZINDO/S method strongly overestimated the intramolecular charge-transfer (ICT) transitions experimentally observed for -OR, -SR, and -NR2 substituted at nonperipheral position phthalocyanines and their analogues in the 450–650 nm region. The hybrid CAM-B3LYP, PBE1PBE, and B3LYP exchange-correlation functionals were found to be much better in predicting energies of such ICT transitions. Overall, we did not find a single exchange-correlation functional that can accurately (MAD < 0.05 eV) and simultaneously predict the energies and the splittings of the Q x and Q y bands as well as energies of the ICT transitions in a large array of substituted and unsubstituted metal-free phthalocyanines and their benzoannulated analogues.

The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL 2 , PcFeL′L″, and [PcFeX 2 ] 2− complexes (Pc = phthalocyaninato(2-) ligand; L = NH 3 , n-BuNH 2 , imidazole (Im), pyridine (Py), PMe 3 , PBu 3 , t-BuNC, P(OBu) 3 , and DMSO; L′ = CO; L″ = NH 3 or n-BuNH 2 ; X = NCO − , NCS − , CN − , imidazolate (Im − ), or 1,2,4triazolate(Tz − )) were probed by electrochemical, spectroelectrochemical, and chemical oxidation as well as theoretical (density functional theory, DFT) studies. In general, energies of the metal-centered occupied orbitals in various six-coordinate iron phthalocyanine complexes correlate well with Lever Electrochemical Parameter E L and intercross the phthalocyaninecentered a 1u orbital in several compounds with moderate-to-strong π-accepting axial ligands. In these cases, an oxidation of the phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally confirmed.

Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mossbauer hyperfine parameters of 36 bisaxially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL 2 , PcFeL′L″, and [PcFeX 2 ] 2− , including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mossbauer quadrupole splittings and the correct trends in experimentally observed isomer shifts. In comparison, hybrid exchange-correlation functionals underestimated quadrupole splittings, while still accurately predicted isomer shifts. Out of ∼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL 2 complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu) 3 ≈ P(OEt) 3 < PMe 3 < P[(CH 2 O) 2 CH 2 ]-p-C 6 H 4 NO 2 < PEt 3 ≈ PnBu 3 ). Natural Bond Orbital (NBO) analysis was successfully used to explain the general trends in the observed quadrupole splitting for all compounds of interest. In particular, the general trends in the quadrupole splitting correlate well with the axial ligand dependent, NBO-predicted population of the 3d z2 orbital of the Fe ion and are reflective of the hypothesis proposed by Ohya and co-workers (Inorg. Chem., 1984, 23, 1303 on the adaptability of the phthalocyanine's π-system toward Fe-L ax interactions. The first X-ray crystal structure of a PcFeL 2 complex with axial phosphine ligands is also reported.