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

Abstract

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

Clarifying the Adsorption of Triphenylamine on Au(111): Filling the HOMO–LUMO Gap

“…No transition energy shifts between the gas phase and adsorbate are detected and the first resonance peak is at the same photon energy as in the gas phase. 6 …”

“…The first peak at about 285 eV originates from C- ortho , C- meta , and C- para contributions of similar intensities, while the smaller peak at 286.5 eV is due to C- ipso contributions. 6 The spectra for each type of C atoms are reported in the Supporting Information . Due to the molecular structure and adsorption orientation, at energies above 291 eV, we observe some polarization effects that are somewhat stronger in the measured spectra, indicating that in the sample the molecules are slightly more rotated or disordered than in the theoretical model.…”

“…The characterization of the adsorption system has been performed by means of photoelectron spectroscopy (PES) and near-edge X-ray absorption fine structure (NEXAFS). Interestingly, the N K-edge NEXAFS spectrum of TPA/Au(111) reveals an extra feature in the pre-absorption edge, which is more intense and extends over a broader energy region compared to a similar pre-edge peak found in the gas-phase spectrum, 6 suggesting that new electronic states are formed between the HOMO and the LUMO of the adsorbed molecule. Our theoretical characterization shows that the new states contain a small contribution from the N atom, and a larger contribution from the C and Au atoms and fill up the molecular HOMO–LUMO gap, which is one of the most important parameters directly connected to the operation of electronic and photovoltaic devices.…”

Efficient Intramolecular Charge‐Transfer Fluorophores Based on Substituted Triphenylphosphine Donors

“…[7] In TPA, the centered nitrogen takes ap lanar sp 2 hybridization due to steric hindrance effects.T he nitrogen 2p z orbital without hybrid stabilization contributes to the HOMO together with the 2p orbitals in the phenyl rings,l eading to as hallow HOMO in TPA. [8] In contrast, the long CÀPb onds in TPP allow TPP apyramid configuration and nonequivalent sp 3 hybridization in phosphorus atom. [9] Thel one electron pair consisting of ahigh ratio of 3s/3p leads to the relatively deep HOMO level.…”

Facile Synthesis of Triphenylamine Based Hyperbranched Polymer for Organic Field Effect Transistors

“…This inherent characteristic makes it more applicable as a hole transport layer in OLEDs and photodiodes [25]. In contrast to BDT, steric hindrance effects cause TPA molecules to assume non-planar structure which suppress molecular agglomeration to a certain degree [26]. Triphenyl amine based copolymers have been explored as a nonvolatile transistor memories [27] and 2D covalent organic framework semiconductor thin films [28].…”