Lateral Interactions and Order–Disorder Phase Transitions of Metal Phthalocyanines on Ag(111)

Abstract

The intermolecular interaction among phthalocyanine molecules deposited on Ag(111) has been investigated at submonolayer coverages. By means of IRAS and SPA-LEED unambiguous evidence for an attractive interaction between neighboring TiOPc molecules is found for dilute layers, which is in contrast to the intermolecular repulsion reported for the CuPc/Ag(111) system. Accordingly, the formation of dense 2D islands of TiOPc molecules with well-defined long-range order (commensurate phase) is observed upon cooling to temperatures below 75 K while a disordered arrangement is retained for adsorbed CuPc. Using DFT calculations as a guide, these differences have been traced to the competition of attractive van der Waals and repulsive electrostatic interactions. Specifically, the vertically oriented molecular dipoles are substantially smaller for adsorbed TiOPc as compared to CuPc due to a compensation of the oppositely oriented dipole moments arising from the Pauli push-back effect on the one hand and the internal molecular dipole associated with the axial Ti-O group on the other. A detailed account and comparison of the molecule-substrate interaction, molecular binding geometries and intermolecular interactions of TiOPc and CuPc on the Ag(111) surface is provided in a theoretical analysis based on DFT.

Adsorption configurations of Co-phthalocyanine on In2O3(111)

“…Combining metalation with modifications by functional side groups makes this p-type semiconductor attractive in photovoltaics [4,5] and catalysis [6]. Surface science investigations of (M)Pc on crystalline metal and metal oxide substrates have provided rich information about structural and electronic details of single molecules [7][8][9][10][11], self-assembly into layers [12][13][14][15][16][17][18][19], and thin film growth behavior [20][21][22]. Another hot topic in this field are single-molecule magnets where the Kondo temperature of MPc is related to the interaction with a metallic substrate [23][24][25][26][27].…”

Molecular origin of structural defects in the zinc phthalocyanine film

“…Therefore, only a few of the MPc molecules on the metal surface were dealt with, including ZnPc on Ag(111). 36–38…”

“…4 eV (alias 380 kJ mol −1 ). 36,38 Should such giant values be taken on trust? Typical MPcs are liable to reduction; 39 so, if these calculations are true, the molecules on the noble metal surface should be converted into the radical anions.…”

“…Therefore, only a few of the MPc molecules on the metal surface were dealt with, including ZnPc on Ag(111). [36][37][38] Reportedly, the MPc-Ag/Au binding energy varies from 1.4 eV to ca. 4 eV (alias 380 kJ mol À1 ).…”

“…S10, ESI †) and some DFT calculations 36,37 (2.9 Å for Co-Ag and 3.0 AE 0.1 Å for Cu/Zn-Ag). On the other hand, researchers 38 obtained the maximal binding energy (3.95 eV), which was allegedly gained within the unprecedented long Cu-Ag distance of 3.2 Å.…”