Articolo in rivista, 2019, ENG, 10.1039/C9CP00954J

The effect of long-range order on intermolecular interactions in organic semiconductors: zinc octaethyl porphyrin molecular thin film model systems

A. Kumar, D. Naumenko, G. Rossi, E. Magnano, S. Nappini, F. Bondino, E. Segoloni, L. Amidani, F. d'Acapito, F. Boscherini, L. Barba, E. Pace, M. Benfatto, S. Casassa and M. Pedio

Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche, TASC Laboratory, Trieste, Italy Dipartimento di Fisica, Università di Trieste, Trieste I-34127, Italy Department of Physics and Astronomy, University of Bologna, Italy Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006 Johannesburg, South Africa Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche, c/o ESRF, Grenoble, France Istituto CNR-IC, Area Science Park Basovizza, Trieste, Italy LNF-INFN, Frascati 00044, Italy Dipartimento di Chimica, Università di Torino and NIS, Nanostructured Interfaces and Surfaces, Centre of Excellence, Via Giuria 5, 10125 Torino, Italy

In order to optimize the performance of devices based on porphyrin thin films it is of great importance to gain a physical understanding of the various factors which affect their charge transport and light-harvesting properties. In this work, we have employed a multi-technique approach to study vacuum deposited zinc octaethyl porphyrin (ZnOEP) thin films with different degrees of long-range order as model systems. An asymmetrical stretching of the skeletal carbon atoms of the porphyrin conformer has been observed and attributed to ordered molecular stacking and intermolecular interactions. For ordered films, a detailed fitting analysis of the X-ray absorption near edge structure (XANES) using the MXAN code establishes a symmetry reduction in the molecular conformer involving the skeletal carbon atoms of the porphyrin ring; this highlights the consequences of increased ?-? stacking of ZnOEP molecules adopting the triclinic structure. The observed asymmetrical stretching of the ? conjugation network of the porphyrin structure can have significant implications for charge transport and light harvesting, significantly influencing the performance of porphyrin based devices.

Physical chemistry chemical physics (Online)

Keywords

Organic semiconductors, Porphyrin thin Film, X-ray absorption spectroscopy, Intermolecular interaction

CNR authors

Boscherini Federico, Kumar Abhishek, Barba Luisa, Nappini Silvia, D Acapito Francesco, Pedio Maddalena, Bondino Federica, Magnano Elena

CNR institutes

IC – Istituto di cristallografia, IOM – Istituto officina dei materiali