Issue 40, 2013

Porphyrin adsorbed on the (10[1 with combining macron]0) surface of the wurtzite structure of ZnO – conformation induced effects on the electron transfer characteristics

Abstract

Electron transfer at the adsorbate–surface interface is crucial in many applications but the steps taking place prior to and during the electron transfer are not always thoroughly understood. In this work a model system of 4-(porphyrin-5-yl)benzoic acid adsorbed as a corresponding benzoate on the ZnO wurtzite (10[1 with combining macron]0) surface is studied using density functional theory (DFT) and time-dependent DFT. Emphasis is on the initial photoexcitation of porphyrin and on the strength of coupling between the porphyrin LUMO or LUMO + 1 and the ZnO conduction band that plays a role in the electron transfer. Firstly, ZnO wurtzite bulk is optimized to minimum energy geometry and the properties of the isolated ZnO (10[1 with combining macron]0) surface model and the porphyrin model are discussed to gain insight into the combined system. Secondly, various orientations of the model porphyrin on the ZnO surface are studied: the porphyrin model standing perpendicularly to the surface and gradually brought close to the surface by tilting the linker in a few steps. The porphyrin model approaches the surface either sideways with hydrogen atoms of the porphyrin ring coming down first or twisted in a ca. 45° angle, giving rise to π-interactions of the porphyrin ring with ZnO. Because porphyrins are closely packed and near the surface, emerging van der Waals (vdW) interactions are examined using Grimme's D2 method. While the orientation affects the initial excitation of porphyrin only slightly, the coupling between the LUMO and LUMO + 1 of porphyrin and the conduction band of ZnO increases considerably if porphyrin is close to the surface, especially if the π-electrons are interacting with the surface. Based on the results of coupling studies, not only the distance between porphyrin and the ZnO surface but also the orientation of porphyrin can greatly affect the electron transfer.

Graphical abstract: Porphyrin adsorbed on the (10 [[1 with combining macron]] 0) surface of the wurtzite structure of ZnO – conformation induced effects on the electron transfer characteristics

Supplementary files

Article information

Article type
Paper
Submitted
19 Apr 2013
Accepted
21 Aug 2013
First published
10 Sep 2013

Phys. Chem. Chem. Phys., 2013,15, 17408-17418

Porphyrin adsorbed on the (10[1 with combining macron]0) surface of the wurtzite structure of ZnO – conformation induced effects on the electron transfer characteristics

M. Niskanen, M. Kuisma, O. Cramariuc, V. Golovanov, T. I. Hukka, N. Tkachenko and T. T. Rantala, Phys. Chem. Chem. Phys., 2013, 15, 17408 DOI: 10.1039/C3CP51685G

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements