Assignment of the optical spectrum of metal porphyrin and phthalocyanine radical anions

Abstract

<jats:p> The approach developed previously to assign the major π → π* and π* → π* bands in the optical spectra of metallophthalocyanine radical species [ MPc (−n)]<jats:sup>(n−2)−</jats:sup> (n = 1–6), which was based on spectral band deconvolution analyses of the UV-vis absorption and magnetic circular dichroism (MCD) spectra and ZINDO calculations, is reviewed in this paper and extended to the major bands observed in the spectrum of the zinc tetraphenylporphyrin radical anion [ ZnTPP (−3)]<jats:sup>−</jats:sup>. The magnetic circular dichroism spectrum is dominated by an intense pseudo A term associated with the B (or Soret) transition with bands at 445 and 465 nm. Weaker bands associated with the π* → π* transition out of the partially filled LUMO give rise to two widely separated, oppositely signed, coupled B terms in the MCD spectrum at 538 and 910 nm. The Q transition is assigned to a weak absorption band at 750 nm and a shoulder slightly to the blue at 728 nm. </jats:p>

Photophysics and spectroscopic properties of zinc phthalocyanine revisited using quantum chemistry

“…The peak related to this transition is difficult to be observed experimentally due to the very small values of oscillator strength (0.007 and 0.019, respectively in gas phase and in DMSO). This state was described by other TD-DFT calculations, 37,39,40 being our value for the gas phase similar to the reported by Nguyen and Pachter, 39 and about 0.4-0.5 eV greater than the reported by Liao et al 37 and Ricciardi et al 40 Using the ZINDO method, 34 a weak transition related to a E u state (p,p*) at 3.72 eV (333 nm) was also found. However, this state presents a different electronic configuration.…”

“…For the isolated system, the intense Q peak transition energy at 2.05 eV is nearly similar to the reported in other TD-DFT calculations (1.96, 2.09 eV), 37,39,40 and more displaced from the data furnished from ZINDO and Slater transition state methods (1.84, 1.76, 1.44 eV). [34][35][36]38 Experimental data in gas phase, under supersonic jet, cryogenic matrix and Ar matrix suggest values related to Q transition between 1.85 and 1.98 eV, 1,20,24,25,27 slightly smaller than our TD-DFT forecast. The inclusion of solvent effects (DMSO) with the IEFPCM model leads to a diminishing of the excitation energy of the Q band, from 2.05 to 1.96 eV, with the consequent shift of the maximum absorption wavelength from 604 to 632 nm.…”

“…Similarly, in other TD-DFT and ZINDO calculations, the authors were also unable to describe this transition. 34,37,39,40 A possibility to elucidate it should be using elaborate multiconfigurational methods, like CASSCF, CASPT2 or MRCI.…”

“…Semi empirical ZINDO method generated orbital ordering similar to that proposed with Gouterman's model. [34][35][36] The time-dependent density functional theory (TD-DFT) has been employed with relative success in several studies. [37][38][39][40][41][42] The effect of peripheral groups on the electronic structure and properties of unbounded and bonded metal phthalocyanines were investigated by Liao et al 37 Liao and Scheiner 38 investigated the electronic structure and bonding in metal phthalocyanines and obtained Q and Soret transition energies.…”

Reactivity of Rare Earth Metal Porphyrins/Phthalocyanines in Acid Media

“…870 nm in such neutral solvent as benzene is also attributed to the double-and tripledecker complex absorption not only for oxidized doubledecker LnPc 2 · bat for neutral LnPc 2 H [82] and triple-decker Ln 2 (PcR 4 )P 2 (R = dinaphto[1,2-e:1',2'-g]-1,4-dioxocine group, P = 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin dianion). [76] ZINDO calculations of molecules, cations and anions of simpl ZnPc using 16-orbital model and data of magnetic circular dichroism [83,84] show that highly symmetric ZnPc demonstrates the orbital degenerated main state: two boundary HOMO are degenerated. When the removal of one electron, on the example of the transition from ZnPc to the ZnPc + , takes place, the similar degeneracy lifting and the appearance of new bands of π→π transition within the occupied shells (π*→π* transition in the case of ZnPc -) together with bathochromic shifted Q bands at 958 and 925 nm, a band of second π→π* transition at 300−450 nm and B 1 , B 2 and n→π * bands are observed.…”