“Excited state C–N bond dissociation and cyclization of tri-aryl amine-based OLED materials: a theoretical investigation.”
J. Vijaya Sundar, V. Subramanian & B. Rajakumar. Phys. Chem. Chem. Phys. 2019, 21, 438-447.

Tri-aryl amines (TAA) such as triphenylamine (TPA) are widely used for designing chromophores fordye-sensitized solar cells (DSSC) and organic light-emitting diodes (OLED). These materials degradeover time and hence result in reduced performance. Therefore, exploring the associated mechanisticpathways and factors controlling the degradation is necessary for future development of durableTAA-based devices. Hence, in this study, the complete active space self-consistent-field (CASSCF)method coupled with second order N-electron valence perturbation theory (NEVPT2) calculations wascarried out to understand the excited state phenomena occurring inTAAusingTPAandN,N-diphenyl-2-naphthylamine (DPNA) as model systems. The results indicated the presence of a conical intersectionbetween ground and first excited singlet states with C–N bond dissociation, which acts as a channel forthe excited molecules to dissociate and form radical fragments (phenyl/naphthyl). This occurrence isunusual for non-saturated bonds with delocalization. The resulting radical fragments formed intra-molecular products and subsequently yielded five- and six-membered cyclized products depending onthe type of aryl groups. The significant findings from this study throw light on the photostability ofTAA-based OLED devices as well as on the possible route to synthesize cyclic amines such as carbazoles.