Electronic Structure of One-Dimensional Biradical Molecular Chain
- PDF / 27,642,319 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 195 Views
Electronic Structure of One-Dimensional Biradical Molecular Chain H. Koike1, K.Ogawa1, T. Kubo2, K. Uchida2, M. Chikamatsu3, R. Azumi3, K. Mase4, K. Kanai1 1 Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan 2 Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan 3 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan 4 KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan ABSTRACT We investigated electronic structure of one-dimensional biradical molecular chain which is constructed by exploiting the covalency between organic molecules of a diphenyl derivative of sindacenodiphenalene (Ph2-IDPL). To control the crystallinity, we used gas deposition method. Ultraviolet photoelectron spectroscopy (UPS) revealed developed band structure with wide dispersion of the one-dimensional biradical molecular chain. INTRODUCTION London dispersion forces are responsible for the aggregation of closed-shell organic molecules. In most cases, intermolecular interactions between organic molecules with a closedshell configuration are much weaker than intramolecular interactions such as covalent bonds because of their relatively small intermolecular overlap of wave functions. In fact, previous studies using ultraviolet photoelectron spectroscopy (UPS) have experimentally found a small band dispersion width, W (e.g., BTQBT thin film: W ≈ 0.4 eV, Pentacene thin film: W ≈ 0.46 eV) [1,2]. Kubo et al. reported synthesis of a delocalized singlet biradical hydrocarbon, diphenyl derivative of s-indacenodiphenalene (Ph2-IDPL) [3]. The ground state of Ph2-IDPL molecule is described by the resonance structure between Kekulé and biradical structures. Ph2-IDPL consists of two coplanar phenalenyl units linked by a s-indacene moiety. Phenalenyl is well-known stable organic radical that bears an unpaired electron in singly occupied molecular orbital (SOMO). Its biradical nature causes strong coupling between the molecules. In the Ph2-IDPL crystal, Ph2-IDPL forms a quasi-one-dimensional molecular chain in a slipped stacking arrangement with an extremely short average π-π stacking distance of 3.137 Å (figure 1 (a)) [3]. Figure 1 (b) indicates simulated bonding orbital of the trimmer. The orbitals are spread in the intermolecular spaces showing covalency. Therefore, Ph2-IDPL is a suitable material for our aim to investigate electronic structure of one-dimensional biradical molecular chain.
Downloaded from https:/www.cambridge.org/core. Columbia University Libraries, on 07 Jun 2017 at 17:48:46, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/opl.2014.63
Figure 1. (a) One-dimensional molecular chain of Ph2-IDPL (Ph: phenyl). (b) Simulated molecular orbital of Ph2-IDPL trimmer. (Molecular orbital calculation was performed based on density functional theory by using the GAUSSIAN 09 package at the PW91/6-31G* level.) EXPERIMENT Ph2-IDPL was prepared according to the literat
