Lone-Pair Delocalization Effects within Electron Donor Molecules: The Case of Triphenylamine and Its Thiophene-Analog

• DOI: 10.1021/acs.jpcc.8b06475
• Publication Date: 2018-07-12T18:28:51Z
• Authors: T. Zhang; I. E. Brumboiu; C. Grazioli; A. Guarnaccio; M. Coreno; M. de Simone; A. Santagata; H. Rensmo; B. Brena; V. Lanzilotto; C. Puglia
• Keywords: HOMO/LUMO; Lone pair; Triphenylamine; XANES; Electronegativity

Triphenylamine (TPA) and its thiophene-analog, N,N-diphenyl-2-thiophenamine (DPTA), are both well-known as electron-donating molecules implemented in optoelectronic devices such organic solar cells LEDs. Comprehensive valence core level photoelectron spectroscopy, well near edge X-ray absorption spectroscopy (NEXAFS), measurements have been performed on gas phase TPA DPTA. The experimental results compared to density functional theory calculations, providing a detailed description of the molecular electronic structure. Specifically, C 1s lines DPTA were resolved different atom contributions their binding energies explained result two counter-acting effects: (1) electronegativity nitrogen (and sulfur DPTA) (2) delocalization N S lone-pair electrons. In addition, K-edge NEXAFS spectrum reveals that lowest unoccupied orbital (LUMO) energy position is affected differently if core–hole site phenyl thiophene ring. properties these largely by significant contribution electrons (pz) highest occupied orbital. LUMO empty states ring explains better performance donor−π–acceptor containing this moiety photoenergy conversion devices.