A nonlinear optical (NLO) ternary exciplex is developed using a two-photon absorbing acceptor material tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), a two-photon absorbing donor material 4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC), and a linear optical acceptor material 2,4,6-tris(1,1′-biphenyl)-1,3,5-triazine (T2T). In the ternary mixture, the high-energy exciplex TAPC:3TPYMB and the low-energy exciplex TAPC:T2T generate an effective synergy effect on the basis of their reverse intersystem crossing (RISC) channels to achieve further utilization of triplet excitons, giving rise to significantly enhanced one- and two-photon excited fluorescence properties. The highest photoluminescence quantum yield (PLQY) of the ternary exciplex 3TPYMB:TAPC:T2T measured in air atmosphere is ∼77.8%, which is greatly improved compared to that of the binary exciplex TAPC:T2T (∼39.6%) and the binary exciplex TAPC:3TPYMB (∼3.7%). More interestingly, the ternary exciplex also exhibits enhanced two-photon excited fluorescence under long-wavelength laser excitation. In comparison, no improvement in PLQY is observed in another ternary exciplex 3TPYMB:4,4′,4″-tris(carbazole-9-yl)triphenylamine (TCTA):T2T, which lacks an effective synergy effect between its high- and low-energy exciplex RISC channels. Our synergistic dual-channel RISC strategy may be helpful for the design of multicomponent thermally activated delayed fluorescence (TADF) NLO materials and facilitate the development of NLO applications. 

Ternary Exciplexes for Enhanced Two-Photon Excited Fluorescence by the Synergy Effect of Dual Reverse Intersystem Crossing Channels

Preparation, structure and optical properties of mixed stacked cocrystals of 2,2':6′,2″-Terpyridine and 1,2,4,5-tetracyanobenzene

Novel V-shaped D-π-A-π-D two-photon absorption compounds with large Stokes shifts: Synthesis, optical properties, selective detection of cysteine, and imaging in living cells

The pursuit of high-performance low-cost organic light-emitting materials is a long-term task. The down- and upconverted fluorescence from an electron donor–acceptor host composed of di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole with fluorescent guests, 9,10-bis[N,N-di-(p-tolyl)-amino]anthracene (TTPA) and 5,6,11,12-tetraphenylnaphthacene (rubrene), was investigated. We found that the energy loss mechanism can be greatly suppressed by the effective Förster resonance energy-transfer process from the exciplex host to fluorescent guests. An extremely high photoluminescence quantum yield (PLQY) up to 98.41% was achieved, as well as strong upconverted green, orange, and blue fluorescence was observed in TTPA-, rubrene-, and undoped exciplex blends, respectively, under the excitation of near-infrared femtosecond laser. These low-cost materials with high PLQYs and strong upconverted fluorescence properties may have great application potential in light-emitting devices, lasers, and bioimaging applications. 

Chenghao Liu

Papers

Observation of up-conversion fluorescence from exciplex of m-MTDATA:TPBi blend