Theoretical investigation of aromaticity and charge transfer in emission process of triarylmethyl radicals as OLED materials

Four different kinds of triarylmethyl radicals (TAMs)— tris(2,4,6-trichlorophenyl)methyl radical (TTM), perchlorotriphenyl methyl radical (PTM), (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM), and (N-carbazolyl)bis(2,4,6-tirchlorophenyl)methyl radical (CzBTM)—are investigated theoretically with regard to their structures and electron transition behaviors. Linear correlation has been found between the spin density of α-C and the averaged cosine of the torsion angle, with the correlation coefficient satisfied by R² =.96 by applying the Becke method. The emission energies predicted by PCM-UBMK/6-311++G(d,p)//PCM-UM06-2X/6-31+G(d,p) are reliable for TAMs. Interfragment charge transfer (IFCT) analysis reveals the charge transfer behavior during the excitation. The aromaticity of TAMs is evaluated by NICS(1)zz for the first time. Combined with the IFCT analysis results, the NICS(1)zz values of the acceptor on the ground states are found to be highly correlated with the emission wavelength, and R² is.98 at the PCM-UB3LYP/6-31+G(d,p) level, which can be used for emission spectra prediction and molecular design.