Electron‐Affinity Substituent in 2,6‐Dicarbonitrile Diphenyl‐1λ⁵‐Phosphinine Towards High‐Quality Organic Lasing and Electroluminescence under High Current Injection

Abstract

Rationally manipulating the functional substituents plays a crucial role in tuning the luminescence and lasing properties of organic gain media. Herein, a cyanophenyl-moiety, which exhibits relatively weaker electron affinity, is connected to 2,6-dicarbonitrile diphenyl-1λ 5 -phosphinine (DCNP) via para-linking. Resultantly, the appreciated locally-excited characteristics ensuring a large oscillator strength and high radiative rate can be reserved in DCNP-4-(4-cyanophenyl) (DCNP-pCN). Interestingly, the weak chargetransfer state from the relative donor (D)/acceptor (A) interplay enables small singlet-triplet splitting (ΔE ST ≈ 0.45 eV). Thus the triplets generated on DCNP-pCN can be efficiently scavenged by 4,4'-bis[(N-carbazole)styryl] biphenyl (BSBCz), which is used as the host with a lower-lying triplet energy level for DCNP-pCN. Moreover, benefitting from the mediation between the conjugated length extension and weak D/A interplay, the emission spectrum cannot be largely shifted, which can effectively suppress the overlap between the lasing emission of DCNP-pCN and the excited-state absorption of BSBCz, thereby avoiding detrimental singlettriplet annihilation. Thus, high-quality distributed feedback lasings with ≈2.0 μJ cm −2 thresholds are achieved, and the organic light-emitting diodes exhibit external quantum efficiency exceeding 2.0% without efficiency rolloff under high current injection, indicating the potential for electricalpumping organic lasings.

Low Threshold, High Q-Factor Optically Pumped Organic Lasers and Exciton Dynamics in OLEDs under High Current Density: Singlet–Triplet Annihilation Effect and toward Electrical Injection Lasing

“…For host–guest doping systems, it is necessary to have a large overlap between the emission of host and the absorption of guest to realize efficient energy transfer from host to guest, and the energy transfer rate needs to be as fast as possible for lasing emission within the picosecond time scale . As shown in Figure b, the good spectral overlap guarantees the effective energy transfer between them, which is well proven by the PL emission spectra of mCP:PIO doped films at different doped concentrations, shown in Figure S1a.…”

Effect of intramolecular charge transfer processes on amplified spontaneous emission of D–π–A type aggregation-enhanced emission molecules

“…The ASE phenomenon might be observed in the first stage because the lasing lifetime was in the picosecond timescale. 16,26 However, in Fig. 5a, the non-mirror symmetric relationship between the PL spectrum and the stimulated emission spectrum causes two negative effects which prevents the ASE: (i) the PL peak is far from the stimulated emission region and the distribution of s SE (l) in the stimulated emission region is small, and (ii) most of the PL spectrum is overlapping with the ESA region which induces huge energy loss.…”

A large-scale deep-blue tetraphenylbenzene-bridged hybridized local and charge transfer fluorophore exhibiting small efficiency roll-off and low amplified spontaneous emission threshold

“…6b), which is much lower than that of the common D-A molecules. [48][49][50][51][52] According to the dependence of the PL peak intensity on the stripe length, a gain coefficient (g) of 36.6 cm À1 can be estimated. And the loss coefficient (a) of 8.7 cm À1 is obtained by fitting the PL peak intensity as a function of the distance between the sample edge and the excitation region.…”