Influence of Core Halogenation on the Electronic Structure of Naphthothiadiazole Derivatives

Abstract

Naphthothiadiazoles are promising electron acceptors for applications in organic semiconductor-based (opto)­electronic devices. Here, we studied the structural and electronic properties of naphthothiadiazole (NTD) derivatives adsorbed on Au(111) in the monolayer and thin films using temperature-programmed desorption as well as vibrational and electronic high-resolution electron energy loss spectroscopy. In addition, we performed state-of-the-art quantum chemical calculations to further illuminate electronic properties. In the monolayer and multilayer coverage regime, the NTD derivatives adsorbed in a planar fashion with the molecular backbone oriented parallel to the gold surface. Several singlet and the first triplet transition energies are determined. The optical gap (S0 → S1 transition) in the nonhalogenated parent NTD is found to be 2.6 eV, whereas it is reduced by 200 meV in the chlorinated and brominated NTD. All experimentally observed singlet and triplet transition energies are reduced due to halogenation, which is underlined by theory.

Influence of N-introduction in pentacene on the electronic structure and excited electronic states

“…15–28 High-resolution electron energy loss spectroscopy (HREELS) provides the required insight into both adsorption and electronic properties of molecular compounds at interfaces to (semi)conducting surfaces and within thin films. 11,29–39 Depending on the primary energy of the incident electrons molecular vibrations or electronic transitions can be excited, including optically forbidden transitions (singlet to triplet states) as already successfully demonstrated for some organic compounds 40–42 including also the N-heteropolycycle 6,13-diazapentacene (6,13-DAP). 12 While the adsorption and electronic properties of pentacene (PEN) and its derivatives adsorbed on various metallic substrates have been investigated in great detail (see for example ref.…”

Impact of Connectivity on the Electronic Structure of N-Heterotriangulenes

“…Previous measurements of aromatic Nheteropolycycles have clearly demonstrated that at this coverages the molecules are electronically decoupled from the metallic substrate. [31][32][33]40,43,44 In the HREEL spectrum several electronic transitions are clearly detectable at 3.4, 3.5, 3.85, 3.95, 4.5, and 5.4 eV including also vibrational contributions. The peaks at 3.4 and 3.5 eV in the HREEL spectrum, are the 0−0 and 0−1 vibrational transitions of the S 0 → S 0 excited state, with vibrational contributions of the out-of-plane γ ω (C−N−C) and γ ω (C−H) vibrations with frequencies of about 754 cm −1 (93 meV).…”

Electronic Properties of Tetraazaperopyrene Derivatives on Au(111): Energy-Level Alignment and Interfacial Band Formation

“… 17 The latter can be determined in surface-adsorbed molecules with 2PPE, 10 − 13 , 18 differential reflectance spectroscopy, 19 − 22 or high-resolution electron energy loss spectroscopy. 18 , 23 − 29 …”

“…), which is different from the optical gap (highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) transition leading to exciton formation) . The latter can be determined in surface-adsorbed molecules with 2PPE, − , differential reflectance spectroscopy, − or high-resolution electron energy loss spectroscopy. ,− …”