Electronic properties of CuPc and H2Pc: an experimental and theoretical study

Abstract

Phthalocyanine (H2Pc) and its open-shell copper complex (CuPc) deposited on amorphous gold films have been studied by combining the outcomes of several synchrotron based spectroscopic tools (X-ray photoelectron spectroscopy, UV photoelectron spectroscopy and near-edge X-ray absorption fine structure, NEXAFS, spectroscopy) with those of density functional theory (DFT) calculations. The assignment of experimental evidence has been guided by the results of DFT numerical experiments carried out on isolated molecules. With specific reference to CuPc NEXAFS data collected at the N K-edge, they have been assigned by using the open-shell time-dependent DFT (TDDFT) in the framework of the zeroth order regular approximation (ZORA) scalar relativistic approach. The agreement between theory and experiment has been found to be satisfactory, thus indicating that the open-shell TDDFT (F. Wang and T. Ziegler, Mol. Phys., 2004, 102, 2585) may be used with some confidence to look into the X-ray absorption spectroscopy results pertinent to transition metal complexes. As far as the metal-ligand interaction is concerned, the combined use of NEXAFS spectroscopy and DFT outcomes ultimately testified the significant ionic contribution characterizing the bonding between the metal centre and the nitrogen atoms of the phthalocyanine coordinative pocket.

High resolution NEXAFS of perylene and PTCDI: a surface science approach to molecular orbital analysis

“…28 Time dependent DFT calculations have been successfully extended to treat also core level excitations in heterocyclic aromatics. 29 On the other hand, the renovated interest in NEXAFS simulations of poly-and heterocyclic aromatics is associated with the study of their interaction with substrates of technological interest. In this context, the relevant parameters for understanding the molecule to substrate interaction from NEXAFS measurements are the atom resolved contributions to the absorption spectra and the electronic structure of the unoccupied molecular orbitals, MOs, in the presence of the core-hole.…”

Ligand‐Field Strength and Symmetry‐Restricted Covalency in CuII Complexes – a Near‐Edge X‐ray Absorption Fine Structure Spectroscopy and Time‐Dependent DFT Study

“…More specifically, the relative intensities and relative positions of the X L 2,3 (X = I-III) features satisfactorily agreed with theoretical oscillator strength distributions ( X f). Such a result, combined with estimates of (1) a Cu-S interaction in III more covalent than the Cu-Cl one in I, [9,11] (2) a Cu-N interaction in II less covalent than the Cu-Cl one in I, [11,12] (3) a ligand field in III weaker than that in I [15] and (4) a ligand field in II stronger than that in I [15] represented a successful test of the SO-ZORA TDDFT-TDA method when applied to the modelling of CuII L 2,3 spectra. Interestingly, the composition analysis of the excitations associated with II L 3 revealed that, in addition to 2p 3/2 Ǟ 3d transitions, [18] metal-to-ligand charge-transfer (MLCT) transitions involving low-lying ligand-based π* MOs contribute to the II L 3 intensity and, thus, weaken its believed relationship with the M-L covalency.…”

“…[8, 12,21] The NEXAFS spectra recorded at the Cu II L 2,3 edges of highly oriented thin films of II and IV are displayed in Figure 2.…”

“…[8,9] Recently, [11] some of us have successfully simulated the L 2,3 spectra of I, [8a] copper phthalocyanine (II, Figure 1) [12] and the so-called oxidized blue copper site in plastocyanin (III, Figure 1) [8a,13] through time-dependent density functional theory (TDDFT) calculations within the TammDancoff approximation (TDA) coupled to the relativistic zeroth-order regular approximation (ZORA) including SO effects. More specifically, the relative intensities and relative positions of the X L 2,3 (X = I-III) features satisfactorily agreed with theoretical oscillator strength distributions ( X f).…”

“…Both π 4 The NEXAFS spectra recorded at the Cu II L 2,3 edges of IV deposited as a thin film on Au(100) are presented and discussed with reference to the results of SO-ZORA TDDFT-TDA calculations on the isolated molecule. The adopted computational setup [11,12,26] allowed a comparison with homogeneous literature data pertaining to both I and II. Moreover, insights into the Cu-X (X = Cl, N and O) symmetry-restricted covalency of the different CuX 4 square-planar chromophores have been gained by exploiting both experimentally and theoretically the dependence of NEXAFS spectra of II and IV deposited on Au(100) on the direction of the photon electric field.…”