Ground and Excited States of Zinc Phthalocyanine Studied by Density Functional Methods

Abstract

The first time-dependent DFT study of the excited states of ZnPc is presented. The theoretical results provide an accurate description of the UV−vis and vacuum−UV spectra and prove to be in excellent agreement with gas-phase spectra and generally in line with deconvolution analyses of solution and Ar/matrix absorption and MCD spectra. The nature and intensity of the main spectral features are highlighted and interpreted on the basis of the ground state electronic structure of the complex. A fragment approach where the four benzopyrrole rings and the aza bridges are taken as building blocks has proven to be a very important tool to fully understand the energy and composition of the MOs involved in the transitions and, from these, the excitation energies and intensities. The Gouterman a1u orbital is the HOMO and the assignment of the Q band is conventional and uncontroversial. The B band comprises five Eu excitations, whose positions and intensities are in very good accordance with the deconvolution of the experimental absorption band performed with the help of MCD spectra. However, this deconvolution invokes Jahn−Teller splitting of the Eu states which we have not calculated. We find at the red edge of the B band the weak 2nd π→π* transition and at the blue edge the weak n→π* transition which have been identified in the experiments. We do not confirm at low energy, in the tail of the Q band (the “Q02” region) an electronic origin for the band which has been suggested to arise from the lowest z-polarized n→π* transition. This transition is predicted by our calculations to be very weak and to lie in the B band region. The energies and intensities of the higher excitations are in excellent agreement with the UV N and L bands and with the far UV C and X bands. The predicted level pattern of the lowest triplet excited states fits in with phosphorescence data available and excited-state absorption spectra

Ground and excited states of zinc phthalocyanine, zinc tetrabenzoporphyrin, and azaporphyrin analogs using DFT and TDDFT with Franck-Condon analysis

“…The first TDDFT study of ZnPc by Ricciardi et al used an adiabatic local-density approximation (ALDA) in combination with a statistical average of different orbital potentials (SAOP) for the exchange-correlation potential to solve for the time-dependent density. 25 The Q-band result for the 0-0 transition was close to experimental values: 1.96 eV. 25 The significant contribution of Ricciardi et al was to separate and change the exchange-correlation energy.…”

Muoniated radical states in the organic semiconductor phthalocyanine

“…This would favor the anchoring of muonium to that nitrogen in a dative-bond way, leaving the conjugated structure of the inner carbon-nitrogen ring untouched and a nearby unpaired electron. Since the lowest unoccupied molecular orbital ͑LUMO͒ of phthalocyanines is predominantly made up from atomic orbitals belonging to that ring, 22,23 the lingering electron would assume a spatial configuration similar to the LUMO and become more delocalized than in the cases of states I or II.…”

“…The molecule has a lone electron on a half-occupied level positioned in the middle of the HOMO-LUMO gap, corresponding mainly to a 3d x 2 −y 2 character orbital originated from the Cu atom. 22 When an extra electron is added to the molecule, forming the CuPc − ion, it is energetically more favorable to deposit it directly into the LUMO than pairing it with the lone Cu electron in the 3d orbital. Theoretical calculations predict that the configuration having both electrons in the Cu 3d orbital is in fact the first excited state of the CuPc − ion, the ground state being formed with one electron in the Cu 3d orbital and one in the LUMO of the Pc molecule.…”

On the required shape corrections to the local density and generalized gradient approximations to the Kohn–Sham potentials for molecular response calculations of (hyper)polarizabilities and excitation energies

“…Recently, for example, the SAOP potential has been applied successfully to calculation of excitation spectra of transition metal tetrapyrroles and of zinc phthalocyanine, 13,14 and to calculation of polarizability and absorption spectra of alkali metal clusters. 15 Reliable results have been obtained with the BP-GRAC potential for the response properties of furan homologues.…”