In an organic electroluminescent (EL) device, the recombination of injected holes and electrons produces what appears to be an ion‐pair or charge‐transfer (CT) exciton, and this CT exciton decays to produce one photon directly, or relaxes to a low‐lying local exciton (LE). Thus the full utilization of both the energy of the CT exciton and the LE should be a pathway for obtaining high‐efficiency EL. Here, a twisting donor‐acceptor (D‐A) triphenylamine‐imidazol molecule, TPA‐PPI, is reported: its synthesis, photophysics, and EL performance. Prepared by a manageable, one‐pot cyclizing reaction, TPA‐PPI exhibits deep‐blue emission with high quantum yields (90%) both in solution and in the solid state. Fluorescent solvatochromic experiments for TPA‐PPI solutions show a red‐shift of 57 nm (3032 cm−1) from low‐polarity hexane (406 nm) to high‐polarity acetonitrile (463 nm), accompanied by the gradual disappearance of the vibrational band in the spectra with increased solvent polarity. The photophysical investigation and DFT analysis suggest an intercrossed CT and LE excited state of the TPA‐PPI, originating from its twisting D‐A configuration. This is a rare instance that a CT‐state material shows highly efficient deep‐blue emission. EL characterization demonstrates that, as a deep‐blue emitter with CIE coordinates of (0.15, 0.11), the performance of a TPA‐PPI‐based device is rather excellent, displaying a maximum current efficiency of >5.0 cd A−1, and a maximum external quantum efficiency of >5.0%, corresponding to a maximum internal quantum efficiency of >25%. The effective utilization of the excitation energy arising from materials with intercrossed‐excited‐state (LE and CT) characters is thought to be beneficial for the improved efficiency of EL devices.

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Doping an organic crystal such as an inorganic semiconductor without having a bad influence on crystalline quality is a very difficult task because weak intermolecular interactions and lattice mismatches exist in organic condensed states. We report here the successful growth of tetracene and pentacene-doped trans-1,4-distyrylbenzene (trans-DSB) crystals with high crystalline quality, large size, and excellent optical properties. The doped concentration up to 10% can be achieved by controlling the temperature of the crystal growth zone. The first key point for the crystals with a high doping ratio is the choice of the host (trans-DSB) and guest (tetracene or pentacene) molecules with comparable crystal lattice structures, which ensure less lattice mismatch. The second key point is crystal growth at relative high temperatures by the physical vapor transport (PVT) method, which gives the guest molecules high kinetic energy to incorporate into the crystal lattice of the host. These doped crystals with slice shape and large size (millimeter scale) maintain ordered layer structures and crystal surface continuities, which are verified by X-ray diffraction (XRD) and atomic force microscopy (AFM) analysis. Efficient energy transfer from the host to the guest and the suppressing of the interaction among the guest molecules lead to color-tunable emission and high luminescent efficiencies (blue for undoped trans-DSB, η = 65 ( 4%; green for tetracene-doped trans-DSB, η = 74 ( 4%; red for pentacenedoped trans-DSB, η = 28 ( 4%). Steady-state and time-resolved fluorescence spectroscopy of undoped and doped crystals, and their amplified spontaneous emissions, have been investigated. These doped crystals are expected to be of interest for lightemitting transistors, diodes, and electrically pumped lasers.

Sociodemographic and urban landscape characteristics are associated to mortality risk during heat waves and are useful to build heat vulnerability maps.