Aggregation‐induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE ...molecules such as tetraphenylethene (TPE). However, as the family of AIE‐active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzoa,d7annulenylidene (THBDBA), and 5,5′‐bidibenzoa,d7annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).
Luminescence turn‐on: Through theoretical calculations to explain empirical observation, it is now possible to more fully explain the phenomenon of aggregation‐induced emission. By comparing tetraphenylethene and its structurally similar analogues, deeper insight has been gained into this photophysical phenomenon in which luminescence can be turned on in the aggregated or solid state.
Organic emitters with persistent phosphorescence have shown potential application in optoelectronic devices. However, rational design and phosphorescence tuning are still challenging. Here, a series ...of metal-free luminophores without heavy atoms and carbonyl groups from commercial/lab-synthesized carbazole and benzene were synthesized to realize tunable molecular emission from fluorescence to phosphorescence by simply substituent variation. All the molecules emit blue fluorescence in both solution and solid state. Upon removal of excitation source, the fluorinated luminophores show obvious phosphorescence. The lab-synthesized carbazole based molecules exhibit a huge lifetime difference to the commercially purchased ones due to the existence of isomer in the latter samples. The small energy gap between singlet and triplet state and low reorganization energy help enhance intersystem crossing to contribute to a more competitive radiative process from triplet to ground state. Blue and white organic light-emitting devices are fabricated by using fluorinated luminophore as emitting layer.
Fluorescence imaging in near-infrared IIb (NIR-IIb, 1500-1700 nm) spectrum holds a great promise for tissue imaging. While few inorganic NIR-IIb fluorescent probes have been reported, their organic ...counterparts are still rarely developed, possibly due to the shortage of efficient materials with long emission wavelength. Herein, we propose a molecular design philosophy to explore pure organic NIR-IIb fluorophores by manipulation of the effects of twisted intramolecular charge transfer and aggregation-induced emission at the molecular and morphological levels. An organic fluorescent dye emitting up to 1600 nm with a quantum yield of 11.5% in the NIR-II region is developed. NIR-IIb fluorescence imaging of blood vessels and deeply-located intestinal tract of live mice based on organic dyes is achieved with high clarity and enhanced signal-to-background ratio. We hope this study will inspire further development on the evolution of pure organic NIR-IIb dyes for bio-imaging.
The development of single molecule white light emitters is extremely challenging for pure phosphorescent metal-free system at room temperature. Here we report a single pure organic phosphor, namely ...4-chlorobenzoyldibenzothiophene, emitting white room temperature phosphorescence with Commission Internationale de l'Éclair-age coordinates of (0.33, 0.35). Experimental and theoretical investigations reveal that the white light emission is emerged from dual phosphorescence, which emit from the first and second excited triplet states. We also demonstrate the validity of the strategy to achieve metal-free pure phosphorescent single molecule white light emitters by intrasystem mixing dual room temperature phosphorescence arising from the low- and high-lying triplet states.The development of single molecule white light-emitters is extremely challenging for pure phosphorescent metal-free systems at room temperature. Here the authors show a single pure organic room temperature phosphor, 4-chlorobenzoyldibenzothiophene, utilizing the emission from both T
and T
states.
All-inorganic CsPbI
perovskite quantum dots have received substantial research interest for photovoltaic applications because of higher efficiency compared to solar cells using other quantum dots ...materials and the various exciting properties that perovskites have to offer. These quantum dot devices also exhibit good mechanical stability amongst various thin-film photovoltaic technologies. We demonstrate higher mechanical endurance of quantum dot films compared to bulk thin film and highlight the importance of further research on high-performance and flexible optoelectronic devices using nanoscale grains as an advantage. Specifically, we develop a hybrid interfacial architecture consisting of CsPbI
quantum dot/PCBM heterojunction, enabling an energy cascade for efficient charge transfer and mechanical adhesion. The champion CsPbI
quantum dot solar cell has an efficiency of 15.1% (stabilized power output of 14.61%), which is among the highest report to date. Building on this strategy, we further demonstrate a highest efficiency of 12.3% in flexible quantum dot photovoltaics.
Pure organic materials with ultralong room‐temperature phosphorescence (RTP) are attractive alternatives to inorganic phosphors. However, they generally show inefficient intersystem crossing (ISC) ...owing to weak spin–orbit coupling (SOC). A design principle based on the realization of small energy gap between the lowest singlet and triplet states (ΔEST) and pure ππ* configuration of the lowest triplet state (T1) via structural isomerism was used to obtain efficient and ultralong RTP materials. The meta isomer of carbazole‐substituted methyl benzoate exhibits an ultralong lifetime of 795.0 ms with a quantum yield of 2.1 %. Study of the structure–property relationship shows that the varied steric and conjugation effects imposed by ester substituent at different positions are responsible for the small ΔEST and pure ππ* configuration of T1.
A design principle based on the realization of the small energy gap between the lowest singlet and triplet states (ΔEST) and pure ππ* configuration of the lowest triplet state (T1) via structural isomerism was used to obtain efficient and ultralong room temperature phosphorescence materials. The meta isomer of carbazole‐substituted methyl benzoate exhibits an ultralong lifetime of 795.0 ms with a quantum yield of 2.1 %.
The development of intelligent materials, in particular those showing the highly sensitive mechanoresponsive luminescence (MRL), is desirable but challenging. Here we report a design strategy for ...constructing high performance On-Off MRL materials by introducing nitrophenyl groups to molecules with aggregation-induced emission (AIE) characteristic. The on-off methodology employed is based on the control of the intersystem crossing (ISC) process. Experimental and theoretical investigations reveal that the nitrophenyl group effectively opens the nonradiative ISC channel to impart the high sensitivity and contrast On-Off behavior. On the other hand, the twisted AIE luminogen core endows enhanced reversibility and reduces the pressure required for the luminescence switching. Thin films can be readily fabricated from the designed materials to allow versatile applications in optical information recording and haptic sensing. The proposed design strategy thus provides a big step to expand the scope of the unique On-Off MRL family.
To reveal the association between retinal microvasculature changes and coronary heart disease (CHD), we assessed the full retinal thicknesses of eight areas, the vessel density of four layers ...(consisting of nine areas) and the flow area in two layers with optical coherence tomography angiography (OCTA) in CHD patients and healthy controls. The mean vessel density of several layers was significantly lower in patients. The difference in choroid capillary flow (negative correlation) between the two groups was significant. Decreased vessel density and blood flow were associated with coronary artery and branch stenosis. The decreases in retinal vessel density, choroidal vessel density, and blood flow area are closely related to coronary artery and branch stenosis.
Because of their innate ability to store and then release energy, long‐persistent luminescence (LPL) materials have garnered strong research interest in a wide range of multidisciplinary fields, such ...as biomedical sciences, theranostics, and photonic devices. Although many inorganic LPL systems with afterglow durations of up to hours and days have been reported, organic systems have had difficulties reaching similar timescales. In this work, a design principle based on the successes of inorganic systems to produce an organic LPL (OLPL) system through the use of a strong organic electron trap is proposed. The resulting system generates detectable afterglow for up to 7 h, significantly longer than any other reported OLPL system. The design strategy demonstrates an easy methodology to develop organic long‐persistent phosphors, opening the door to new OLPL materials.
A novel approach to achieve a pure organic long‐persistent luminescent material using a phosphonium salt doped with dimethylaniline is reported. The doped crystals can exhibit a green afterglow emission lasting up to 7 h after the cessation of UV excitation. The positive phosphonium salt holds and protects the separated charge to produce unprecedented afterglow duration.
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