DFT Studies on the Ground State, First Singlet Excited State, and Triplet State of Triphenylamine and Its Dimer

Density functional theory (DFT) calculations were carried out to study triphenylamine and its dimer linked by methyl groups in order to understand the degeneracy and conjugation in Wannier organic small molecule (OSM) dimers. Both molecules’ structures are optimized in the ground state S0, the first singlet excited state S1, and the triplet state T1, with dichloromethane and toluene as the solvents, at the B3LYP/6-31+g(d,p) level of theory. We report optimized parameters for each state of each molecule in each solvent, as well as the UV-Vis, phosphorescence, and fluorescence spectra. The dimer’s combination of electronic degeneracy and conjugation result in a higher absorption intensity at longer wavelengths than triphenylamine, which could pave the way for future pivotal research in the rational design of OSMs for organic solar cells by allowing simultaneous absorption intensity to increase and wavelength tunability. A discussion was made on the analysis of coherent double excitations unique to Wannier OSM dimers.