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Luminescence from organic clusters has gained increasing interest recently because of their distinct emission characteristics compared with the monomer, such as color tunable emission with different wavelength excitations. Herein, we reported three lactams with different ring-members of heterocyclics: indolin-2-one (OID), 3,4-dihydroquinolin-2(1H)-one (OID-6) and 1,3,4,5-tetrahydro-2H-benzo[b]azepin-2-one (OID-7) with dual persistent room-temperature phosphorescence (p-RTP) in the crystalline state owing to the formation of clusters. Due to the dual p-RTP with different but comparable phosphorescence lifetimes of multiple triplet states, it is of interest that OID-6 and OID-7 exhibit time-dependent afterglow color emissions from blue to green to yellow, and this is the first report on organic crystalline clusters with time-dependent color-tunable dual persistent room-temperature phosphorescence. The longest phosphorescence lifetime and the highest photoluminescence quantum yield among these three compounds were observed for OID-7 with the most twisted molecular configuration, owing to the simultaneously suppressed triplet quenching and intramolecular vibrational relaxation by the small orbital overlap due to its weak π–π stacking and strong intermolecular hydrogen bonding interactions in the crystalline state. [ABSTRACT FROM AUTHOR]

Luminescence behaviors in organic emitters are influenced greatly by the molecular conformation. However, the current research on room-temperature phosphorescence (RTP) mainly focuses on fixed molecular conformation, such as that in single crystals and rigid hosts. Herein, by linking the phenothiazine moiety with nitrogen heterocycles, we constructed four phenothiazine derivates having planar structure in the ground state. In the excited state, a large conformation relaxation occurs to give a dynamically tunable fluorescence and phosphorescence by the extent of the intramolecular charge transfer (ICT). In systems with a reduced ICT character, multiple emissions consisting of fluorescence and phosphorescence were observed and a white light emission was obtained in the amorphous film state. When increasing the ICT, strong spin mixing between the singlet and triplet occurs in the twisted intramolecular charge transfer (TICT) state, which is favorable for a short triplet lifetime. The emission of the thermally activated delayed fluorescence (TADF) or short RTP depends on the allowance or forbidden of fluorescence in the twisted excited state conformation. This work demonstrates the adjustment of the singlet and triplet emission behaviors through controlling the extent of TICT and provides an insight into the relationship between the molecular conformation and triplet exciton dynamics for future applications. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) photodetection has great application prospects in the fields of space exploration, environmental science and biomedicine. In this work, we will present VUV-sensitive AlN single crystalline films (SCFs) with low defect density, grown by our independently designed in-plane enhanced hetero-epitaxial method. By combining the as-grown films with p-type graphene (p-Gr) serving as a transparent conductive layer, a VUV photovoltaic detector with a p-Gr/i-AlN/n-GaN structure was constructed. At zero bias, the detector exhibits an ultrafast response time of 2.86 μs, which is 2 orders of magnitude faster than that of a previously reported h-BN photoconductive detector. Besides, it also has an ultra-high photovoltage of 2 V and an excellent spectral selectivity. The results have demonstrated that the in-plane enhanced epitaxy strategy is expected to provide reference for the preparation of high-quality AlN and to promote the development of VUV detectors in deep space science. [ABSTRACT FROM AUTHOR]

The effect of boronic ester substitution on the room-temperature phosphorescence properties of phenoxathiine-based derivatives was thoroughly investigated. A significantly improved phosphorescence quantum efficiency of up to 20% in the crystalline state was achieved by delicate molecular manipulation for both enhanced spin–orbital coupling and compact intermolecular packing. [ABSTRACT FROM AUTHOR]