Fig. 4: Time-resolved spectroscopy.
From: Efficient near-infrared organic light-emitting diodes with emission from spin doublet excitons
a, Excited-state singlet (S1) and doublet (D1) population kinetics extracted from transient absorption of neat MADN and MADN:TTM-TPA 3% films under 400 nm excitation. The decay of S1 in the blend and the matching rise of D1 are due to rapid singlet–doublet FRET. b, Comparison of D1 population kinetics for CBP:TTM-TPA 3% and MADN:TTM-TPA 3% films under radical-only 532 nm excitation. Faster decay observed in the MADN blend is indicative of doublet–triplet energy transfer. c,d, Transient PL profiles averaged over 720–880 nm for radical emission following host-selective (400 nm, 330 nm; c) and radical-selective (532 nm; d) excitation. Delayed radical emission is observed in the MADN blend under both host and radical excitation. e, Temperature-dependent transient PL profiles of MADN:TTM-TPA 3% excited at 532 nm. Delayed radical emission is faster at elevated temperatures. f, Arrhenius plot for the MADN:TTM-TPA 3% system revealing a small activation energy for delayed radical emission.
