Wenwen Luo

Biocompatible Green and Red Fluorescent Organic Dots with Remarkably Large Two-Photon Action Cross Sections for Targeted Cellular Imaging and Real-Time Intravital Blood Vascular Visualization.

Fluorescent organic dots are emerging as promising bioimaging reagents because of their high brightness, good photostability, excellent biocompatibility, and facile surface functionalization. Organic dots with large two-photon absorption (TPA) cross sections are highly desired for two-photon fluorescence microscopy. In this work, we report two biocompatible and photostable organic dots fabricated by encapsulating tetraphenylethene derivatives within DSPE-PEG matrix. The two organic dots show absorption maxima at 425 and 483 nm and emit green and red fluorescence at 560 and 645 nm, with high fluorescence quantum yields of 64% and 22%, respectively. Both organic dots exhibit excellent TPA property in the range of 800-960 nm, affording upon excitation at 820 nm remarkably large TPA cross sections of 1.2×10(6) and 2.5×10(6) GM on the basis of dot concentration. The bare fluorophores and their organic dots are biocompatible and have been used to stain living cells for one- and two-photon fluorescence bioimagings. The cRGD-modified organic dots can selectively target integrin αvβ3 overexpressing breast cancer cells for targeted imaging. The organic dots are also applied for real-time two-photon fluorescence in vivo visualization of the blood vasculature of mouse ear, providing the spatiotemporal information about the whole blood vascular network. These results demonstrate that the present fluorescent organic dots are promising candidates for living cell and tissue imaging.

Integration of aggregation-induced emission and delayed fluorescence into electronic donor–acceptor conjugates

A series of luminogens comprised electron donors and acceptors are found to possess two types of interesting photophysical processes of aggregation-induced emission (AIE) and delayed fluorescence. According to theory calculation, restriction of intramolecular motions accounts for their AIE characteristics. Moreover, a separated distribution of the HOMOs and the LUMOs of these luminogens leads to small ΔEST values and therefore delayed fluorescence.

Sky-blue nondoped OLEDs based on new AIEgens: ultrahigh brightness, remarkable efficiency and low efficiency roll-off

Two novel AIEgens decorated with fluorenyl and dimesitylboryl groups are prepared. They show high thermal stability and excellent solid-state photoluminescence efficiency. Sky-blue nondoped OLEDs are achieved based on them, affording remarkable electroluminescence efficiencies (12.2 cd A−1 and 5.3%), ultrahigh brightness (92810 cd m−2) and low efficiency roll-off (11.0 cd A−1 at 1000 cd m−2).

Improving Electron Mobility of Tetraphenylethene-Based AIEgens to Fabricate Nondoped Organic Light-Emitting Diodes with Remarkably High Luminance and Efficiency

Robust light-emitting materials with strong solid-state fluorescence as well as fast and balanced carrier transporting ability are crucial to achieve high-performance organic light-emitting diodes (OLEDs). In this contribution, two linear tetraphenylethene (TPE) derivatives (TPE-TPAPBI and TPE-DPBI) that are functionalized with hole-transporting triphenylamine and/or electron-transporting 1,2-diphenyl-1H-benzimidazole groups are synthesized and fully characterized. Both TPE-TPAPBI and TPE-DPBI have aggregation-induced emission attributes and excellent photoluminescence quantum yields approaching 100% in vacuum deposited films. They also possess good thermal property, giving high decomposition temperatures (480 and 483 °C) and glass-transition temperatures (141 and 157 °C). TPE-TPAPBI and TPE-DPBI present high electron mobilities of 1.80 × 10(-5) and 1.30 × 10(-4) cm(2) V (-1) s(-1), respectively, at an electric field of 3.6 × 10(5) V cm(-1), which are comparable or even superior to that of 1,3,5-tri(1-phenylbenzimidazol-2-yl)benzene. The nondoped OLED device employing TPE-TPAPBI as active layer performs outstandingly, affording ultrahigh luminance of 125 300 cd m(-2), and excellent maximum external quantum, power and current efficiencies of 5.8%, 14.6 lm W(-1), and 16.8 cd A(-1), respectively, with very small roll-offs, demonstrating that TPE-TPAPBI is a highly promising luminescent material for nondoped OLEDs.

Solution-processable, star-shaped bipolar tetraphenylethene derivatives for the fabrication of efficient nondoped OLEDs

Organic light-emitting diodes (OLEDs) based on solution-processable small molecules are attracting intense attention, as such technology combines the merits of low-cost solution processability of polymers and finely defined structural uniformity of small molecules. Small-molecule tetraphenylethene (TPE) derivatives are excellent solid-state light emitters featuring aggregation-induced emission (AIE) characteristics, however those that can be used in solution-processable devices are very rare. To address this issue, herein, a series of novel star-shaped bipolar TPE derivatives are synthesized and characterized. Their thermal stabilities, photophysical properties, electronic structures, electrochemical behaviors, and application in solution-processed OLEDs are investigated systematically. These luminogens exhibit AIE characteristics and excellent fluorescence quantum yields up to 95% in the solid state. Nondoped OLEDs are successfully fabricated through a spin-coating method. The solution-processed OLEDs [ITO (130 nm)/PEDOT:PSS (40 nm)/emitter (70 nm)/TPBi (30 nm)/Ba (4 nm)/Al (120 nm)] adopting star-shaped TPE derivatives as light-emitting layers show peak luminance of 11 665 cd m−2 and high electroluminescence (EL) efficiencies up to 8.3 cd A−1, 2.6% and 7.5 lm W−1. These results demonstrate a promising avenue towards efficient nondoped OLEDs based on solution-processable AIE-active small molecules.

New AIEgens with delayed fluorescence for fluorescence imaging and fluorescence lifetime imaging of living cells

A series of luminogens with both aggregation-induced emission and delayed fluorescence features are synthesized and characterized. Biocompatible fluorescent nanoparticles are fabricated by encapsulating them within a bovine serum albumin matrix, and perform well in fluorescence imaging and fluorescence lifetime imaging of living cells.

Oxidation-enhanced emission: exploring novel AIEgens from thieno[3,2-b]thiophene S,S-dioxide

Luminescent materials with high thiophene contents generally suffer from severe emission quenching in the aggregated state, owing to various active nonradiative decay channels. Herein, we report that a series of novel propeller-like luminogens consisting of a thieno[3,2-b]thiophene S,S-dioxide core and different phenyl rotors can behave oppositely. They show faint emission in solutions, but can fluoresce strongly in solid films, displaying prominent aggregation-induced emission (AIE) nature. Crystallographic, computational, and spectroscopic results reveal the synergistic effect of a propeller-like conformation and the oxidation of thieno[3,2-b]thiophene to thieno[3,2-b]thiophene S,S-dioxide greatly enhances emission efficiency of the luminogen in solid film. Calculation and electrochemical experiments reveal that they have much lower LUMO energy levels than the unoxidized counterparts. This work not only presents a feasible approach to create robust luminescent materials from thiophene by oxidation but also provides a new AIE platform with advantages of structural variety, high solid-state emission efficiency, and strong electron affinity for optoelectronic and biological applications.

Steric, conjugation and electronic impacts on the photoluminescence and electroluminescence properties of luminogens based on phosphindole oxide

Aggregation-induced emission (AIE) is currently receiving intense interest because of its important implications in photophysics. The structure-property relationship decipherment of AIE luminogens is of crucial importance for the fundamental understanding and application exploration. In this research, a series of novel luminogens based on phosphindole oxide (PIO), including a peculiar one with a folded conformation and apparent through-space conjugation, were synthesized and studied as models to elucidate the AIE mechanism. The significant impacts of steric, conjugation and electronic effects on the AIE property are presented based on the results of crystallography analysis, optical spectra measurements and theoretical computation. Non-doped yellow organic light-emitting diodes were fabricated with the new PIO-based luminogens, and they exhibited high brightness, good electroluminescence efficiencies and low efficiency roll-off.

Oligo(maleic anhydride)s: a platform for unveiling the mechanism of clusteroluminescence of non-aromatic polymers

Luminescent materials without conventional aromatic groups have attracted extensive attention in recent years. However, the luminescence mechanism has been obscure and debatable. In the present study, based on oligo(maleic anhydride)s (OMAhs), alternative polymer of poly[(maleic anhydride)-alt-(2,4,4-trimethyl-1-pentene)] (PMP) and copolymers containing different ratios of OMAhs, we have proposed that the luminescence of OMAhs stems from the cluster. Moreover, a mechanism of clusteroluminescence was studied in detail with the assistance of theoretical simulation, which attributed the phenomenon to the intra- and inter-chain n → π* interaction of carbonyl groups of SAh units in OMAhs. Thus, the proposed study will give insights into designing luminescent materials with nonconventional groups.

Aggregation-enhanced emission and through-space conjugation of tetraarylethanes and folded tetraarylethenes

Aggregation-induced emission luminogens (AIEgens) are attracting rapidly increasing interest, due to their promising applications in various research frontiers. Tetraarylethenes are the most extensively studied AIEgens, which are usually prepared by McMurry couplings. In this study, we prepare not only new folded tetraarylethenes, but also tetraarylethanes by the McMurry coupling of different diarylmethanones. Moreover, the crystal structures, photophysical properties, orbital distributions, thermal stabilities and electrochemical behaviors of tetraarylethanes and folded tetraarylethenes are investigated. The new luminogens show through-space conjugation and aggregation-enhanced emission with high solid-state emission efficiencies approaching unity. Non-doped OLEDs based on the folded tetraarylethenes are fabricated, which perform well, affording high luminance up to 49 030 cd m−2 and good electroluminescence efficiencies of 6.6 cd A−1 and 2.5%.