Dual Intramolecular Charge-Transfer Fluorescence Derived from a Phenothiazine-Triphenyltriazine Derivative

Abstract

A material containing a phenothiazine (PTZ) electron donor unit and 2,4,6-triphenyl-1,3,5-triazine (TRZ) electron acceptor unit, PTZ-TRZ, which exhibits thermally activated delayed fluorescence (TADF) was developed. Density functional theory calculations revealed the existence of two ground-state conformers with different energy gaps between the lowest singlet excited state and lowest triplet excited state (1.14 and 0.18 eV), which resulted from the distortion of PTZ, as confirmed by X-ray structure analysis. PTZ-TRZ in toluene solution showed two broad, structureless emissions, confirming the existence of two different excited states. From detailed analyses of the absorption and photoluminescence spectra, we determined that both emissions were intramolecular charge-transfer (ICT) fluorescence. Therefore, the excited-state conformers of PTZ-TRZ resulted in dual ICT fluorescence. Because previously reported dual fluorescence from single molecules involves locally excited and ICT fluorescence, the dual ICT fluorescence from PTZ-TRZ is novel. Temperaturedependence of transient PL spectra of a 2 wt % PTZ-TRZ-doped film in 3,3′-bis(N-carbazolyl)-1,1′-biphenyl measured by a streak camera revealed that the former and latter emissions were independent of and dependent on the film temperature, respectively. This confirms that the dual fluorescence involves TADF characteristics. An organic light-emitting diode containing PTZ-TRZ exhibited a maximum external quantum efficiency of 10.8 ± 0.5% with dual ICT fluorescence.

Horizontal molecular orientation in solution-processed organic light-emitting diodes

“…4(a). 17,25,26 The EL spectra of the OLEDs displayed in Fig. 4(b) are found to be very similar to the PL spectra in Fig.…”

Highly efficient electroluminescence from purely organic donor–acceptor systems

“…Both of these approaches can effectively decrease the HOMO-LUMO spatial overlap. Examples of electron-donating units that can induce large twist angles include phenoxazine [18-20, 30, 31, 34, 36, 38, 44], phenothiazine [35], phenazine [30,37], and 9,9-dimethylacridane [30,34]. Donor-acceptor systems bridged by a spiro structure also possess good HOMO-LUMO separation and small ΔE ST [14,15,24,33].…”

Aggregation-induced delayed fluorescence from phenothiazine-containing donor–acceptor molecules for high-efficiency non-doped organic light-emitting diodes

“…A similar AIE behavior was also observed for PTZ-BP in THF/water mixtures (Figure 3b), whereas the only structural difference between the two compounds is that PTZ-XT contains an oxygen bridge, which Aggregation-induced delayed fluorescence N Aizawa et al restricts the internal rotations in the acceptor unit. Hence, the observed AIE behaviors of PTZ-XT and PTZ-BP are primarily attributed to aggregation-induced restriction of conformational changes in the phenothiazine donor unit [42][43][44] and the rotation around the single bond between the donor and acceptor units.…”