The photoluminescence quantum yield (FPL) in degassed dilute THF solution is 33%, which decreased under air to 25%. No delayed emission was observed in THF and the lifetime, tPL, is 22.4 ns (Figure ). 1.18× 10 7 a In THF solutions (10 -5 M). b Measured in evaporated thin films consisting of 1.5 wt% emitter in TSPO1 host under vacuum. lexc = 280 nm. c Steady-state emission maximum at 300 K. lexc = 365 nm. d Full width at half maximum of the emission peak. e S1 and T1 energies were obtained from the onsets of the respective prompt fluorescence (delay: 1 ns; gate time: 100 ns) and phosphorescence spectra (delay: 1 ms; gate time: 9 ms) at 77 K. λexc = 343 nm. f 2-MeTHF glass (10 -6 M). g DEST = E(S1) -E(T1). h Relative photoluminescence quantum yields (ΦPL) in solutions were measured by the relative method using quinine sulfate as a standard (Φr = 54.6% in 1 N H2SO4). Absolute ΦPL of thin films were measured using an integrating sphere. i Prompt and delayed lifetimes obtained by TCSPC and MCS, respectively. λexc = 379 nm. j Intersystem and reverse intersystem crossing rates were calculated using steady-state approximation method as described in literature. We next explored the potential of this compound as an emitter in an OLED. Of the suitably high triplet energy hosts investigated (TSPO1, DPEPO, PPT, and mCP), the highest FPL of 71% was obtained when the emitter is doped in TSPO1 host at 1.5 wt%; the FPL of this film reduced to 33% upon exposure to air (see Table for host matrix FPL study), suggesting strongly that there are accessible triplet excited states. The PL spectrum of NOBNacene is red-shifted by 5 nm in the 1.5 wt% TSPO1 doped film compared to in THF solution (Figure ). The FWHM of the emission spectrum in the doped film is 38 nm (0.26 eV). The high-energy peak around 410 nm is the dominant one and there is a low-energy shoulder at 430 nm, consistent with the theoretical calculations. The emission of NOBNacene is redshifted by 12 nm from DOBNA (lPL = 398 nm, FPL = 58%, in 1 wt% PMMA). The ΔEST is 0.30 eV in the 1.5 wt% TSPO1 thin film, a value that is nearly identical to that observed in 2-MeTHF (Figure ).