Tianyu Han

Aggregation-Induced Emission Enhancement of Aryl-Substituted Pyrrole Derivatives

The relationship between the structures and light emission properties of five aryl-substituted pyrrole derivatives was studied during aggregation in THF-water mixtures. Only pentaphenylpyrrole clearly shows, however, an aggregation-induced emission enhancement (AIEE) phenomenon. On comparison of the optical properties and single-crystal structures of these pyrrole derivatives, it is suggested that the more twisted configuration which prevented parallel orientation of conjugated chromophores combined with the restricted intramolecular rotation (RIR) effect was the main cause of the AIEE phenomenon.

A highly sensitive, single selective, real-time and “turn-on” fluorescent sensor for Al3+ detection in aqueous media

A “turn-on” fluorescent sensor, sodium 4,4′,4′′-(1H-pyrrole-1,2,5-triyl)tri-benzoate (Py(PhCOO-Na)3), has been prepared for the detection of Al3+ in aqueous solution. The detection mechanism, as well the mechanism specific to Al3+, was studied by fluorescence spectroscopy, UV-vis spectroscopy and dynamic light scattering (DLS) measurement. Py(PhCOONa)3 exhibited an aggregation-induced emission (AIE) characteristic and was found to show a specific affinity to Al3+, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Upon binding Al3+, a significant fluorescence enhancement with a turn-on ratio of over 10-fold was triggered by the AIE process. Moreover, this sensor is highly selective for Al3+ over other metal ions with a detection limit of 5 μM and a quantitative detection range of 5–120 μM, and is able to be used in the determination of Al3+ in drinking water. The time-response investigation indicates that the emission intensity of (Py(PhCOO−)3) can be quickly boosted to reach the maximum intensity in less than 10 s upon titration of Al3+.

Defect-sensitive crystals based on diaminomaleonitrile-functionalized Schiff base with aggregation-enhanced emission

In this work, we report the synthesis and photophysical studies of a new luminogen, A3MN, a diaminomaleonitrile-functionalized Schiff base. A3MN is aggregation-enhanced emission (AEE)-active: the emission of A3MN is enhanced with the aggregate formation. A3MN also possesses twisted intramolecular charge transfer (TICT) properties, showing noticeable solvatofluorochromism. Interestingly, the crystals of A3MN are nonemissive; the defect areas of the crystal, however, are highly emissive, as confirmed by spectroscopic methods and confocal microscopy. By taking advantage of this defect sensitive feature, a “turn-on” type of mechanofluorochromic material is developed, the emission of which is significantly enhanced under pressure or shear force. The detection limit reaches 0.1 Newton owing to its “turn-on” nature. Such defect-induced emission also renders A3MN sensitive to various kinds of mechanical actions, including hitting, friction, sculpture, and ultrasonic vibration.

A diethylaminophenol functionalized Schiff base: crystallization-induced emission-enhancement, switchable fluorescence and application for security printing and data storage

In this study, we report the synthesis and photoluminescence (PL) behaviour of a new luminogen, SBOH, a diethylaminophenol functionalized Schiff base. SBOH possesses electron donor (D) and acceptor (A) units, showing twisted intramolecular charge transfer (TICT) properties. Interestingly, SBOH is weakly emissive in the amorphous phase but becomes highly emissive upon crystallization as confirmed by spectroscopic methods and fluorescence microscopy; in other words, SBOH is crystallization-induced emission-enhancement (CIEE)-active. Similar to the typical CIEE luminogens, the emission of SBOH is also sensitive to molecular packing modes. The weak emission of amorphous SBOH can be switched on via a deprotonation process caused by strong alkali. Meanwhile, exposure to acetic acid vapour rapidly switches the emission to the “off” state through re-protonation. The protonation and deprotonation processes display good reversibility. This deprotonation process is further confirmed by 1H NMR analysis and UV-vis spectroscopy. By taking advantage of the stimuli responsive fluorescence, a convenient and efficient technology for security printing and data storage is designed.

Stimuli-responsive fluorophores with aggregation-induced emission: implication for dual-channel optical data storage

For optical data storage (ODSes), fluorescence may be an ideal computer-readable signal on account of its scalability, correction capability, and potentially enhanced capacity. In this study, we report the synthesis and photoluminescence (PL) behaviour of a class of fluorophores with electron donor and acceptor units. They exhibit AIE properties with long-wavelength emission colour. Owing to the reactive electron withdrawing group, their emission spectra have shown either “on–off” switching or a remarkable blue-shift upon alkali treatment. The changes in their fluorescence are due to TICT–LE transition as confirmed by their absorption spectra and DFT calculation. The fluorescent response can be recovered or not, depending on the chemical stimulant used for encoding. Based on the stimuli-responsive nature of the fluorophores, we have further developed both rewritable and write-once read-many (WORM) ODSes with single or dual-channel outputs. “0” and “1” state of the encoded binary data, corresponding to the TICT and LE emission, can be read easily using a spectrofluorophotometer. In addition, the WORM ODSes enjoy the advantage of long-term stability and the rewritable ODSes can be reused many times without fatigue.

DMF-induced emission of an aryl-substituted pyrrole derivative: a solid thermo-responsive material to detect temperature in a specific range

The aryl-substituted pyrrole derivative, 4-(2,5-diphenyl-1H-pyrrol-1-yl)benzoic acid (TPPA), was found to have a controllable fluorescence in the solid state due to its propeller-shaped molecular design and adjustable molecular packing. Melding a carboxylic acid unit with triphenylpyrrole turned the typical aggregation-induced emission (AIE) luminogen into a luminogen that only emits intensely in a certain aggregation form—i.e., when it is crystallized from dimethyl formamide (DMF). A thermal responsive solid material was developed by exploiting this property. Its fluorescence remained almost unchanged at relatively low temperature ( 85 °C), good reversibility and solvent-free procedure make TPPA a thermo-responsive material for use in temperature monitoring devices.

Stoichiometric imbalance-promoted synthesis of polymers containing highly substituted naphthalenes: rhodium-catalyzed oxidative polycoupling of arylboronic acids and internal diynes

A new route for the synthesis of functional polymers was developed. Oxidative polycoupling of 4,4′-(α,ω-alkylenedioxy) bis(diphenylacetylene)s with phenylboronic acid and (1,1,2-triphenylvinyl)phenylboronic acid, respectively, was catalyzed by [Cp*RhCl2]2 and oxidants in dimethylformamide, affording soluble polymers with highly substituted naphthalene rings in satisfactory yields with moderate molecular weights. All the polymers were thermally and morphologically stable, showing high thermal-degradation and glass-transition temperatures of 317–404 °C and 95–168 °C, respectively. They were film-forming and their thin solid films showed high refractive indices (RI = 1.7414–1.6038) in a wide wavelength region of 400–1600 nm. The polymer carrying tetraphenylethene unit was weakly emissive in solution but emitted intensely in the condensed phase, displaying a phenomenon of aggregation-induced emission. The emission of its nanoaggregates could be quenched by picric acid with large quenching constants, making it promising as a sensitive chemosensor for efficient detection of explosives.

Diaminomaleonitrile-based Schiff bases: aggregation-enhanced emission, red fluorescence, mechanochromism and bioimaging applications

Here we report the synthesis of two diaminomaleonitrile-based Schiff bases with a donor–acceptor structure and an aggregation-enhanced emission feature. By changing the alkyl chain length in the donor unit, a red-emitting material with remarkable mechanochromic properties and applications in bioimaging was generated due to the J-aggregate formation in the solid state.

Mechanochromic luminogen with aggregation-induced emission: implications for ink-free rewritable paper with high fatigue resistance and low toxicity

In this study, we report the synthesis and photoluminescence (PL) behaviour of a new luminogen, DHBA, a functionalized Schiff base. The twisted molecular conformation together with the incorporation of electron donor–acceptor pairs endow the luminogen with both aggregation-induced emission and twisted intramolecular charge transfer properties. The crystalline luminogen shows strong green emission at around 514 nm while the emission colour turns orange-red (562 nm) with a big loss in the quantum efficiency after grinding. The colour of the ground sample can be readily converted back into the initial state though recrystallization by either immersing or fuming in organic solvents. The conversion can be implemented for more than 30 cycles, showing good repeatability. This luminogen probably shows the highest fatigue resistance among all the mechanochromic compounds that have been reported. Inspired by the unique mechanochromism, an archetype of ink-free rewritable paper is developed. Letters and patterns can be easily written using pressure and erased by fumigation in handwriting experiments. The luminogen also enjoys the advantages of a one-pot synthesis and low biotoxicity, providing a reliable candidate for green rewritable paper technology to fulfill demands for sustainability and carbon mitigation.

Solvent-assistant self-assembly of an AIE+TICT fluorescent Schiff base for the improved ammonia detection.

Solvent-assistant self-assembly of an AIE+TICT fluorescent Schiff base into one-dimensional nanofilaments has been developed. The orientation of the assemblies can be controlled by a simple dewetting process: the filaments are interweaved when the self-assembly process is performed on a horizontal substrate, while tilting the substrate to a tiny angle results in the formation of highly oriented ones with long-range order as verified by microscopic examination. The compound shows remarkable fluorescent response to ammonia gas based on a TICT-LE transition. The self-assembled film presents higher detection sensitivity compared with the non-assembled test paper: the former enables 4.75 times faster response time and 6.86 times lower detection limit than the latter. Furthermore, the former demonstrates better selectivity toward ammonia gas in the presence of various organic amines. The sensing devices also enjoy the advantage of cyclic utilization. The fluorescence of the fumed devices can be converted back into the original state when they are heated at 100 °C for 5 min, as thermal treatment can desorb the ammonia gas that adsorbed in the sensing devices.