Molecular torsion controls the excited state relaxation pathways of multibranched tetraphenylpyrazines: effect of substitution of morpholine vs. phenoxazine

Multibranched donor-acceptor derivatives exhibiting desirable photophysical properties are efficiently used in optoelectronic devices, in which the excited state relaxation dynamics of the derivatives control the efficiency of the devices. Here, the effect of intramolecular torsion on the excited state relaxation dynamics of tetraphenylpyrazine (TPP) derivatives in non-polar (toluene) and polar (THF) solvents is investigated by substituting the electron donor of morpholine (TPP-4MOP) and phenoxazine (TPP-4PHO) leading to the planar and twisted configurations, respectively, using femtosecond and nanosecond transient absorption spectroscopy. In the steady state, TPP-4MOP showed feeble emission (ΦF ∼0.03) due to the weak donor by the delocalization of electron density supported by theoretical optimization. The TPP-4PHO exhibited strong emission (ΦF ∼0.18) in toluene compared to that in THF, in which it showed a large Stokes shift (∼9691 cm-1) with low fluorescence quantum yield (ΦF ∼0.01). The observation of large Stokes shifts, inherent nature and theoretical calculations of TPP-4PHO suggest the twisting of the dihedral angle between tetraphenylpyrazine and phenoxazine in the excited state leading to the twisted intramolecular charge transfer state (TICT). The femtosecond and nanosecond transient absorption and picosecond time-resolved emission spectra of TPP-4PHO revealed the signature of the existence of both the partial TICT and TICT states in THF leading to the triplet state. Whereas in the case of TPP-4MOP, the transient absorption spectra showed the formation of the triplet state from the local excited state without the involvement of the TICT state. Aggregation studies of TPP-4PHO in a THF and water mixture reflect the elimination of the TICT state by the restriction of intramolecular torsion in the aggregates leading to an increase of 12-fold of the fluorescence intensity along with shifting of the maximum towards the blue region. These studies revealed that the excited state relaxation pathways of the derivatives are controlled by polarity-dependent torsional motion.

Dendritic polyphenylene AIEgens: fluorescence detection of explosives and stimulus-responsive luminescence

Dendritic AIEgens with polyphenylene peripherals and TPE luminescent core had shown detection capability to picric acid and tunable response to external stimulus.

Chromophoric Dendrimer-Based Materials: An Overview of Holistic-Integrated Molecular Systems for Fluorescence Resonance Energy Transfer (FRET) Phenomenon

Dendrimers (from the Greek dendros → tree; meros → part) are macromolecules with well-defined three-dimensional and tree-like structures. Remarkably, this hyperbranched architecture is one of the most ubiquitous, prolific, and recognizable natural patterns observed in nature. The rational design and the synthesis of highly functionalized architectures have been motivated by the need to mimic synthetic and natural-light-induced energy processes. Dendrimers offer an attractive material scaffold to generate innovative, technological, and functional materials because they provide a high amount of peripherally functional groups and void nanoreservoirs. Therefore, dendrimers emerge as excellent candidates since they can play a highly relevant role as unimolecular reactors at the nanoscale, acting as versatile and sophisticated entities. In particular, they can play a key role in the properties of light-energy harvesting and non-radiative energy transfer, allowing them to function as a whole unit. Remarkably, it is possible to promote the occurrence of the FRET phenomenon to concentrate the absorbed energy in photoactive centers. Finally, we think an in-depth understanding of this mechanism allows for diverse and prolific technological applications, such as imaging, biomedical therapy, and the conversion and storage of light energy, among others.

Artificial Light-Harvesting Systems Based on AIEgen-branched Rotaxane Dendrimers for Efficient Photocatalysis

Aiming at the construction of novel platform for efficient light harvesting, the precise synthesis of a new family of AIEgen-branched rotaxane dendrimers was successful realized from an AIEgen-functionalized [2]rotaxane through a controllable divergent approach. In the resultant AIE macromolecules, up to twenty-one AIEgens located at the tails of each branches, thus making them the first successful example of AIEgen-branched dendrimers. Attributed to the solvent-induced switching feature of the rotaxane branches, the integrated rotaxane dendrimers displayed interesting dynamic feature upon the aggregation-induced emission (AIE) process. Moreover, novel artificial light-harvesting systems were further constructed based on these AIEgen-branched rotaxane dendrimers, which revealed impressive generation-dependent photocatalytic performances for both photooxidation reaction and aerobic cross-dehydrogenative coupling (CDC) reaction.

Aggregation-Induced Emission Properties in Fully π-Conjugated Polymers, Dendrimers, and Oligomers

Aggregation-Induced Emission (AIE) in organic molecules has recently attracted the attention of the scientific community because of their potential applications in different fields. Compared to small molecules, little attention has been paid to polymers and oligomers that exhibit AIE, despite having excellent properties such as high emission efficiency in aggregate and solid states, signal amplification effect, good processability and the availability of multiple functionalization sites. In addition to these features, if the molecular structure is fully conjugated, intramolecular electronic interactions between the composing chromophores may appear, thus giving rise to a wealth of new photophysical properties. In this review, we focus on selected fully conjugated oligomers, dendrimers and polymers, and briefly summarize their synthetic routes, fluorescence properties and potential applications. An exhaustive comparison between spectroscopic results in solution and aggregates or in solid state has been collected in almost all examples, and an opinion on the future direction of the field is briefly stated.

Precise Molecular Design for High-Performance Luminogens with Aggregation-Induced Emission

Precise design of fluorescent molecules with desired properties has enabled the rapid development of many research fields. Among the different types of optically active materials, luminogens with aggregation-induced emission (AIEgens) have attracted significant interest over the past two decades. The negligible luminescence of AIEgens as a molecular species and high brightness in aggregate states distinguish them from conventional fluorescent dyes, which has galvanized efforts to bring AIEgens to a wide array of multidisciplinary applications. Herein, the useful principles and emerging structure-property relationships for precise molecular design toward AIEgens with desirable properties using concrete examples are revealed. The cutting-edge applications of AIEgens and their excellent performance in enabling new research directions in biomedical theranostics, optoelectronic devices, stimuli-responsive smart materials, and visualization of physical processes are also highlighted.

TPE-containing amphiphilic block copolymers: synthesis and application in the detection of nitroaromatic pollutants

Two AIE block copolymers termed P1 and P2 bearing TPE and PEG-based chains were synthesized with moderate molecular weights and narrow PDIs via RAFT polymerization. Both P1 and P2 can be used in the fluorescence detection of nitroaromatic compounds (NACs) and cell images.

Rotaxane-branched dendrimers with aggregation-induced emission behavior

By introducing a 9,10-distyrylanthrance (DSA) moiety as the core, we demonstrated the synthesis of a new family of rotaxane-branched dendrimers G1–G3 through the controllable divergent approach.

Amphiphilic triphenylamine–benzothiadiazole dyes: preparation, fluorescence and aggregation behavior, and enzyme fluorescence detection

Change of aggregate stabilization based on removal of the galactopyranose moiety leads to an emission enhancement to detect β-galactosidase activity.

A sequential enzyme-activated and light-triggered pro-prodrug nanosystem for cancer detection and therapy

A sequential enzyme-activated and light-triggered pro-prodrug has been developed for cancer biomarker detection and on-demand therapy.

Peripherally diketopyrrolopyrrole-functionalized dendritic oligothiophenes – synthesis, molecular structure, properties and applications

Structure defined DPP functionalized conjugated thiophene dendrimers with a narrow optical band gap and a high TPA cross section are reported.

Polysiloxane-Modified Tetraphenylethene: Synthesis, AIE Properties, and Sensor for Detecting Explosives

Polysiloxane-modified tetraphenylethene (PTPESi) is successfully synthesized by attaching tetraphenylethene (TPE) units onto methylvinyldiethoxylsiloxane and subsequent polycondensation. Introducing polysiloxane into TPE has minimal effect on the photophysical properties and aggregation-induced emission behavior of TPE. The highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels of PTPESi are located mainly on the tetraphenylethene moieties. The fluorescence intensity and the half width of the emission peak of PTPESi before and after annealing at 120 °C for 12 h are nearly the same, indicating high thermal stability and morphological stability. In addition, use of PTPESi film as a sensor toward the vapor-phase detection of explosives is also studied and it displays quite high fluorescence quenching efficiency and good reversibility.

Fluorescent nanoparticles based on AIE fluorogens for bioimaging

Fluorescent nanoparticles (FNPs) have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance in imaging. Compared with conventional molecular probes including small organic dyes and fluorescent proteins, FNPs based on aggregation-induced emission (AIE) fluorogens have shown significant advantages in tunable emission and brightness, good biocompatibility, superb photo- and physical stability, potential biodegradability and facile surface functionalization. In this review, we summarize the latest advances in the development of fluorescent nanoparticles based on AIE fluorogens including polymer nanoparticles and silica nanoparticles over the past few years, and the various biomedical applications based on these fluorescent nanoparticles are also elaborated.

Aggregation-induced emission enhancement and living cell imaging of novel diarylanthracene conjugated dyes

Diarylanthracene conjugated dyes with good aggregation-induced emission enhancement (AIEE) properties were synthesized and their BSA nanoparticles were successfully used in HeLa cell imaging.

Excited-state localization and energy transfer in pyrene core dendrimers with fluorene/carbazole as the dendrons and acetylene as the linkages

Multi-scale theoretical model and spectra simulation for dendrimers combining TD-DFT/DFT and semi-empirical methods.

Turn-on-type emission enhancement and ratiometric emission color change based on the combination effect of aggregation and TICT found in the hexaazatriphenylene-triphenylamine dye in an aqueous environment

Turn-on-type emission enhancement and a ratiometric emission color change were achieved simultaneously due to the aggregation and TICT of a donor–acceptor-type dye.

Polymeric AIE-based nanoprobes for biomedical applications: recent advances and perspectives

The development of polymeric luminescent nanomaterials for biomedical applications has recently attracted a large amount of attention due to the remarkable advantages of these materials compared with small organic dyes and fluorescent inorganic nanomaterials. Among these polymeric luminescent nanomaterials, polymeric luminescent nanomaterials based on dyes with aggregation-induced emission (AIE) properties should be of great research interest due to their unique AIE properties, the designability of polymers and their multifunctional potential. In this review, the recent advances in the design and biomedical applications of polymeric luminescent nanomaterials based on AIE dyes is summarized. Various design strategies for incorporation of these AIE dyes into polymeric systems are included. The potential biomedical applications such as biological imaging, and use in biological sensors and theranostic systems of these polymeric AIE-based nanomaterials have also been highlighted. We trust this review will attract significant interest from scientists from different research fields in chemistry, materials, biology and interdisciplinary areas.

Complex from ionic β-cyclodextrin polyrotaxane and sodium tetraphenylthiophenesulfonate: restricted molecular rotation and aggregation-enhanced emission

Because restricted intramolecular rotation (RIR) is the main mechanism responsible for the aggregation-enhanced emission (AEE), we thus used a rigid polyrotaxane to impose effective RIR for an water-soluble and AEE-active luminogen of TPS.

Light-emitting properties of donor–acceptor and donor–acceptor–donor dyes in solution, solid, and aggregated states: structure–property relationship of emission behavior

In a polar aqueous environment, a series of triphenylamine-based donor–acceptor-type dyes showed efficient light emission upon the formation of aggregates.

Rigid Jeffamine-included polyrotaxane as hydrogen-bond template for salicylideneazine with aggregation-enhanced emission

A Jeffamine-included polyrotaxane (JCD) was used as rigid template to impose effective rotational restriction on the AIE-active luminogen of 1,2-bis(2,4-dihydroxybenzylidene)hydrazine (CN₄OH).

Synthesis and the aggregation induced enhanced emission effect of pyrene based polysiloxanes

A pyrene based polysiloxane (PySQ) has been successfully synthesized, which shows aggregation induced enhanced emission (AIEE) and the AIEE effect endows PySQ with a longer photoluminescence lifetime as determined by transient photoluminescence decay measurements.

Colour-tunable fluorescence of single molecules based on the vibration induced emission of phenazine

Combining the vibration of the phenazine unit (S0) and the intramolecular energy transfer (IET) effect, compound M1–M4 exhibited color-tunable fluorescence even white emission in two different ways.

N-Unsubstituted-1,2,3-triazole-tethered, AIEE type conjugated polymer as a ratiometric fluorescence probe for silver ions

Selective fluorescence ratiometric detection of Ag⁺ was achieved by a N-unsubstituted-1,2,3-triazole decorated, aggregation-induced emission enhancement (AIEE) type conjugated polymer.

Dendritic AIE-active luminogens with a POSS core: synthesis, characterization, and application as chemosensors

Two nano-hybrid dendrimers were synthesized by grafting tetraphenylethene units onto a POSS core, and were used as chemosensors for picric acid and Ru³⁺ ions.

How is the AIE mechanism profoundly changed in an ESIPT family: the novel introduction of a tetraphenylethene group onto (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2(1H)-one

The first example showing that the AIE mechanism can be completely changed from restriction of TICT to RIR by the introduction of a tetraphenylethene group onto a molecule with ESIPT character is reported herein.

Highly emissive excited-state intramolecular proton transfer (ESIPT) inspired 2-(2′-hydroxy)benzothiazole–fluorene motifs: spectroscopic and photophysical properties investigation

Efficient solid state emission of fluorene–benzothiazole motifs via ESIPT process have been discussed experimentally and theoretically.

Tetraphenylethene end-capped [1,2,5]thiadiazolo[3,4-c]pyridine with aggregation-induced emission and large two-photon absorption cross-sections

New two-photon absorption dyes (TPEPT1 and TPEPT2) were designed and synthesized. These materials show different 2PA properties and unique AIE effects, in which TPEPT1 with higher brightness was used to perform a cell-imaging proposal.

Probing the dendritic architecture through AIE: challenges and successes

Since the aggregation-induced emission (AIE) phenomenon is very sensitive to steric hindrance, we set out to use it as a tool to probe the periphery of dendrimers.

AIE macromolecules: syntheses, structures and functionalities

A comprehensive review of macromolecules with aggregation-induced emission attributes is presented, covering the frontiers of syntheses, structures, functionalities and applications.