Observation of aligned dipoles and angular chromism of exciplexes in organic molecular heterostructures

This study investigates the dipole characteristics of Frenkel and charge-transfer excitons (exciplexes) in organic heterostructures, specifically a bilayer of 4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA) donor and 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T) acceptor molecules. Back focal plane photoluminescence images reveal that exciplex dipoles align perpendicular to Frenkel exciton dipoles. Angular chromism, observed in the 100 meV range, suggests delocalization and potential angle-sensing applications. The blue shift of photoluminescence with increasing excitation power is attributed to repulsive aligned exciplex dipoles with a long lifetime (4.65 µs). Electroluminescence spectra from organic light-emitting diodes (OLEDs) show a blue shift with increasing bias, further supporting unidirectional exciplex dipole alignment. This observation of aligned exciplex dipole moments enhances the coupling of exciton species and improves OLED efficiency.

Sang-hun Lee, Taek Joon Kim, Eunji Lee, Dayeong Kwon, Jeongyong Kim, Jinsoo Joo