Research Theme

Electronic Property of Functional Organic Materials

Keywords

Photoelectron Spectroscopy, Molecular Film, Electronic State

Functional organic materials (FOM) have recently attracted considerable attention both for fundamental research and device applications because of peculiar properties not found in inorganics and small molecules. However the mechanisms and its origin of various device characteristics are still under debate. Scientific mysteries would be are raised because people have believed that electronic structure of FOM would be conserved as in an isolated molecule for solid phases due to van der Waals interaction. To reveal characteristics of FOM the key investigation is precise experiments on the electronic structure at various interfaces, including organic-organic and organic inorganic (metal/semiconductor) contacts. In these systems, the impacts of weak interaction on the electronic structure would appear as small intensity modulation of photoelectron-emission fine features depending on adsorption and aggregation on the surface. By recent development in the instrumental we can assess hidden fine structures in the electronic states, e.g. electron-phonon coupling, quasi-particle states, very small DOS in the HOMO-LUMO gap, narrow band dispersion and dynamic electronic polarization. To elucidate what happens for the FOM at the interface upon weak interaction, an evaluation on the wave-function spread of the electronic sstates is very important because the interface state of physisorbed system is described to be a delocalized molecular orbital state depending on the weak interaction (from vdW interaction to hybridization). Seeing a modification of electron wave function upon weak electronic coupling as well as strong electron-phonon coupling is central issue on our agenda.

A rich assortment in the structure of functional molecular materials and variety in the photoelectron spectral feature.

Selected Publications

1. F. Bussolotti, et al.,“Hole-phonon coupling effect on the band dispersion of organic molecular semiconductors”, Nat. Commun. 8, 173-179 (2017).
2. C. Gaul, et. al.,“Insight into doping efficiency of organic semiconductors from the analysis of the density of states in n-doped C₆₀ and ZnPc”, Nature Materials 17、439-444 (2018).
3. M. Schwarze et. al.,“Molecular Parameters Responsible for Thermally Activated Transport in Doped Organic Semiconductors”, Nature Materials 18, 242-248 (2019).
4. K. Fukutani et. al.,“Detecting photoelectrons from spontaneously formed excitons”, Nature Physics 17, 1024-1030 (2021).
5. K. Sun et. al., "On-surface synthesis of disilabenzene-bridged covalent organic frameworks", Nature Chemistry, 14(12) (2022).