Electronic structure modifications induced by increased molecular complexity: from triphenylamine to m-MTDATA

Area of Science:

• Materials Science
• Physical Chemistry
• Organic Electronics

Background:

• Starburst molecule 4,4',4''-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) is crucial in optoelectronics due to its electron-donor properties.
• Triphenylamine (TPA) is a foundational building block for m-MTDATA, with its electronic structure well-studied.

Purpose of the Study:

• Investigate the gas-phase electronic structure of m-MTDATA for the first time.
• Compare the electronic properties of m-MTDATA with TPA to understand the effect of molecular size and nitrogen content.
• Provide a comprehensive description of m-MTDATA's molecular electronic structure.

Main Methods:

• Photoelectron Spectroscopy (PES) for electronic structure analysis.
• Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy.
• Density Functional Theory (DFT) calculations to complement experimental data.

Main Results:

• C 1s photoelectron spectra of m-MTDATA and TPA show similarities due to competing electronegativity and lone-pair delocalization effects.
• m-MTDATA exhibits a distinct three-peak feature in the valence binding energy region, attributed to N 2pz orbitals from increased nitrogen content.
• A reduced HOMO-LUMO gap was observed for m-MTDATA, indicating enhanced electron-donating capabilities compared to TPA.

Conclusions:

• The electronic structure of m-MTDATA is well-described by combining PES, NEXAFS, and DFT.
• Increasing molecular size and nitrogen content in m-MTDATA significantly impacts its electronic properties, particularly enhancing electron donation.
• m-MTDATA presents improved optoelectronic potential over TPA due to its modified electronic structure and lower HOMO-LUMO gap.