Dual-state Emission Research Articles

Rational design and synthesis of pyrrolo-pyridine dinitrile dyes with strong dual-state emission

In recent years, there has been a growing focus on organic dual-state emission (DSE) materials that demonstrate robust luminescence in both solid and solution states. Nevertheless, in the solid state, π-π stacking between organic molecules often results in pronounced luminescence quenching, posing a significant challenge for the design and synthesis of organic DSE materials. In this work, a pyrrolo-pyridine dinitrile (PPDN) dye was synthesized from commercially available 2-heteroaryl acetonitriles and classical diketopyrrolopyrrole (DPP) dye via a two-step process. Due to its special "J"-shaped planar conjugate structure, the PPDN dye has strong DSE performance, high molar extinction coefficients (ε), large Stokes shifts, and excellent optical and thermal stability. It also has aniline vision detection capability, which is useful in the field of security displays and anti-counterfeiting.

Stimuli-Induced Fluorescence Switching in Azine-Containing Fluorophores Displaying Resonance-Stabilized ESIPT Emission.

This article reports the synthesis, along with structural and photophysical characterization of 2-(2'-hydroxyphenyl)benzazole derivatives functionalized with various azaheterocycles (pyridine, pyrimidine, terpyridine). These compounds show dual-state emission properties, that is intense fluorescence both in solution and in the solid-state with a range of fluorescent color going from blue to orange. Moreover, the nature of their excited state can be tuned by the presence of external stimuli such as protons or metal cations. In the absence of stimuli, these dyes show emission stemming from anionic species obtained after deprotonation (D* transition), whereas upon protonation or metal chelation, ESIPT process occurs leading to a stabilized and highly emissive K* transition. With the help of extensive ab initio calculations, we confirm that external stimuli can switch the nature of the transitions, making this series of dyes attractive candidates for the development of stimuli-responsive fluorescent ratiometric probes.

Multifunctional N-fused fluorescent probes for detection of iron ions and nitro explosives

In this work, two novel probes 4a and 4b were synthesized through Suzuki-Miyaura coupling reaction, whose structures were further confirmed by 1H NMR, 13C NMR, high-resolution mass spectrometry (HRMS) and X-ray single crystal diffraction. The optical properties of the obtained molecules were investigated accordingly. Owing to different bridging fluorophores, there are certain differences in optical performance and detection ability between the two synthesized compounds. Especially, due to the subtle difference in orbitals energy and electron distribution displayed by the DFT calculations, 4a possesses the characteristics of dual-state emission (DSE) molecule, while 4b is an aggregation-induced emission (AIE) molecule. Interestingly, these two molecules can be developed into multifunctional detection probes, successfully applied for the fluorescence recognition of iron ions and common nitroaromatic compounds (NACs). At the same time, the probe molecules can also be applied to the detection of NACs in aqueous environment. What’s more, they can also be loaded on test strips and thin-films for fluorescence identification of NACs, thus being expected to be developed into portable detection tools for NACs.

A dual-state emission luminogen for lipid droplet imaging and photodynamic therapy

Organic luminogens with dual-state emission (DSE) have garnered widespread attention due to their versatility in the forms of both dilute solutions and solids. Despite the growing interest, most research on DSE focuses primarily on molecule design and photophysical investigation, with limited exploration of their practical applications. In this study, we introduce a novel fluorescent molecule, PCT, featuring a distinct D-π(A)-D′ electronic structure. PCT exhibited efficient DSE properties, with high quantum yields in both dilute solutions (ΦTHF = 52.3 %) and solid-state (Φsolid = 74.6 %). Taking advantage of PCT’s lipophilicity, we demonstrated its potential for targeted lipid droplet (LD) imaging in living cells and its utility in monitoring LD depletion during cellular starvation. To further enhance its applicability in photodynamic therapy (PDT), PCT was encapsulated within the amphiphilic triblock copolymer Pluronic F127, forming PCT@F127 nanoparticles with improved colloidal stability. These nanoparticles efficiently generated singlet oxygen (1O2) under white light irradiation, achieving a 1O2 quantum yield of 57.2 %. In vitro studies on MCF-7 cells revealed significant 1O2 generation and potent phototoxicity, leading to marked cell apoptosis and necrosis. These results underscore PCT’s multifunctionality as a DSEgen, with promising applications in both bioimaging and PDT.

The Effects of Pore Defects in π-Extended Pentadecabenzo[9]helicene.

The introduction of precise pore defects into nanocarbon structures results in the emergence of distinct physicochemical characteristics. However, there is a lack of research on non-planar chiral nanographene involving precise pore defects. Herein, we have developed two analogues to the π-extended pentadecabenzo[9]helicene (EP9H) containing embedded pore defects. Each molecules, namely extended dodecabenzo[7]helicene (ED7H; 1) or extended nonabenzo[5]helicene (EN5H; 2), exhibits dual-state emission. Significantly, the value of |glum| of 1 is exceptionally high at 1.41×10-2 in solution and BCPL as 254 M-1 cm-1. In PMMA film, |glum| of 1 is 8.56×10-3, and in powder film, it is 5.00×10-3. This study demonstrates that nanocarbon molecules with pore defects exhibit dual-state emission properties while maintaining quite good chiral luminescence properties. It was distinguished from the aggregation-caused quenching (ACQ) effect corresponding to the nanocarbon without embedded defect. Incorporating pore defects into chiral nanocarbon molecules also simplifies the synthesis process and enhances the solubility of the resulting product. These findings suggest that the introduction of pore defects can be a viable approach to improve nanocarbon molecules.

Hierarchical Self-Assembly and Aggregation-Induced Emission Enhancement in Tetrabenzofluorene-Based Red Emitting Molecules.

The newly synthesized chiral active [5]helicene-like tetrabenzofluorene (TBF) based highly red-emitting molecules exhibit flower-like self-assembly. These molecules display photophysical and structural properties such as intramolecular charge transfer, dual state emission, large fluorescence quantum yield, and solvatochromism. In TBFID, the indandione functional group attached on both sides as the terminal group offers an A-D-A push-pull effect and acts as a strong acceptor to cause more redshift in solution as well as in solid state as compared to TBFPA (TBF with benzaldehyde functional group in terminal position). The self-assembly studies of TBFID demonstrate the aggregation-induced emission enhancement (AIEE) attributed to the restriction of intramolecular rotation at the aggregated state. Furthermore, TBFID shows high quantum yield and intense red emission, making the molecule fit for organic light-emitting diodes (OLED) and bioimaging applications.

Red/near-infrared (NIR) difluoroboron β-diketonate derivatives with reversible mechanochromism for cellular imaging

Near-infrared (NIR) fluorophores have promoted the development of materials for bioimaging, but traditional NIR dyes usually suffer from aggregation-caused quenching (ACQ), impeding their applications. Herein, we propose two difluoroboron β-diketonate complexes TBO and TBS, consisting a donor–acceptor (D-A) structure with triphenylamine (TPA) moiety as an electron donors and difluoroboron as well as furan or thiophene building block as an electron acceptor. The theoretical calculation and optical data shows that both of them have intramolecular charge transfer (ICT) characteristics. Such ICT characteristics endow them with both solvatochromism and dual-state emission (DSE) properties. In the solvent CH2Cl2, the emission wavelength of TBO ranges from 550 nm to 750 nm, with a low fluorescence quantum yield (Φ = 7.0 %). However, in the less polar solvent hexane, the emission wavelength blue-shifts, with an increased Φ reaching up to 18 %. Moreover, TBO and TBS exhibit mechanochromic characteristics and rare multi-channel fluorescence emission phenomena at solid-state. Their solid-state samples can emit fluorescence in four spectral bands with maximum emission wavelengths at 300 nm, 400 nm, 600 nm, and 770 nm under excitation at 240 nm. These unique optical properties are expected to be utilized for detecting polarity of system and deformation. Moreover, according to the results of cell imaging and flow cytometry, TBO molecular were easily internalized into Hela cells and distributed in the cytoplasm with strong red fluorescence. Therefore, this research inspires more insight into development of NIR luminogens for biomedical imaging.

Fluorescent Nanowires from Dual‐State Emitting Fluorophores Directed by Molecular Motors and Aggregation‐Induced Emission: Produce Quantized Light Spectrum

AbstractLuminescent materials require systems that exhibit both dual‐state emission (DSE) and aggregation‐induced emission (AIE) to overcome the limitation of aggregation‐caused quenching (ACQ). Herein, a molecular assembler capable of crafting nanowires that exhibit programmable fluorescence across a broad spectrum of colors in a precisely quantized manner is reported. Because it is a starburst dendritic box made of PAMAM dendrimer (P), controller (C) molecules, and motor (M) molecules, the assembler is called PCM. Here, Nile red is chosen as C and placed into the hollow core of the dendrimer; a double ratchet motor (DRM) is chosen as M and is connected to the N‐terminals of the PAMAM dendrimer. While aqueous dispersed PCM assemblers have broad fluorescence bands beyond 300 nm, their crafted nanowires produce quantized cyan‐green, yellow, and orange‐red light emission in the spectra. These PCM assemblers are shown to hold long‐term memory, rapid switching, and energy harvesting by modulating photonic bandgaps, causing a longer redshift in the solid phase. The DSE of PCM can yield versatile photonics applications like bioimaging and energy harvesting. As PCM nanowires can modulate photonic bandgaps to cause a longer redshift, PCM fluorophores hold promise for drug delivery and cell separation like infrared‐sensitive operations.

Synthesis of Intrinsically-Fluorescent Aliphatic Tautomeric Polymers for Proton-Conductivity, Dual-State Emission, and Sensing/Oxidation-Reduction of Metal Ions.

Herein, fluorescent conducting tautomeric polymers (FCTPs) are developed by polymerizing 2-methylprop-2-enoic acid (MPEA), methyl-2-methylpropenoate (MMP), N-(propan-2-yl)prop-2-enamide (PPE), and in situ-anchored 3-(N-(propan-2-yl)prop-2-enamido)-2-methylpropanoic acid (PPEMPA). Among as-synthesized FCTPs, the most promising characteristics in FCTP3 are confirmed by NMR and Fourier transform infrared (FTIR) spectroscopies, luminescence enhancements, and computational studies. In FCTP3, ─C(═O)NH─, -C(═O)N<, ─C(═O)OH, and ─C(═O)OCH3 subluminophores are identified by theoretical calculations and experimental analyses. These subluminophores facilitate redox characteristics, solid state emissions, aggregation-enhanced emissions (AEEs), excited-state intramolecular proton transfer (ESIPT), and conductivities in FCTP3. The ESIPT-associated dual emission/AEEs of FCTP3 are elucidated by time correlated single photon counting (TCSPC) investigation, solvent polarity effects, concentration-dependent emissions, dynamic light scattering (DLS) measurements, field emission scanning electron microscopy images, and computational calculations. The cyclic voltammetry measurements of FCTP3 indicate cumulative redox efficacy of ─C(═O)OH, ─C(═O)NH─/-C(═O)N<, ─C(─O─)═NH+─/─C(─O─)═N+, and ─C(═N)OH functionalities. In FCTP3, ESIPT-associated dual-emission enable in the selective detection of Cr(III)/Cu(II) at λem1/λem2 with the limit of detection of 0.0343/0.079 ppb. The preferential interaction of Cr(III)/Cu(II) with FCTP3 (amide)/FCTP3 (imidol) and oxidation/reduction of Cr(III)/Cu(II) to Cr(VI)/Cu(I) are further supported by NMR-titration; FTIR and X-ray photoelectron spectroscopy analyses; TCSPC/electrochemical/DLS measurement; alongside theoretical calculations. The proton conductivity of FCTP3 is explored by electrochemical impedance spectroscopy and I-V measurements.

Designing Dual-State and Aggregation-Induced Emissive Luminogens from Lignocellulosic Biosourced Molecules.

Utilizing lignocellulosic biosourced platforms, we synthesized novel cyanostilbene (CS) derivatives featuring the 3,4-dimethoxyphenyl moiety. These derivatives were investigated for their emission properties in both solution and solid states. The two simple CS derivatives exhibit very weak luminescence in solution but significant luminescence in the solid state, indicating distinct Aggregation-Induced Emission (AIE) characteristic. Furthermore, combining these two CS units, without conjugation and with quasi perpendicular orientation, results in a Dual-State Emission (DSE) fluorophore showing luminescence both in solution and solid states. X-ray crystallography studies on the solid-state compounds reveal a structure-emission relationship, demonstrating that the colour emission correlates with the conformations adopted by the molecules in the solid state, which influence the type of stacking.

The influence of positional isomerism of a cyano group of pyrene-based rod-like mesogens on mesomorphism, dual-state emission and multiple applications

Two novel cyanostilbene-based rod-like mesogens consisting of one terminal pyrene and one terminal alkyl chain were prepared by Suzuki coupling and Knoevenagel reactions. The influence of the positional isomerism of the cyano group of cyanostilbene unit on the liquid crystalline characteristics, photophysical characteristics, and mechanochromism characteristics was studied by using polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, absorption spectra, photoluminescence spectra, density functional theory calculation and time-dependent density functional theory calculation. The mesogen in which the cyano group is adjacent to the phenylpyrene unit exhibits a monotropic smectic C phase, whereas the mesogen in which the cyano group is far away from the phenylpyrene unit exhibits an enantiotropic smectic C phase. The mesogen in which the cyano group is adjacent to the phenylpyrene unit exhibits more distinct positive solvatochromism due to more distinct intramolecular charge transfer. The mesogen in which the cyano group is adjacent to the phenylpyrene unit exhibits aggregation-induced emission behavior, but the mesogen in which the cyano group is far away from the phenylpyrene unit exhibits dual-state emission behavior. Reversible mechanochromism behavior could be achieved in both mesogens due to twisted molecular configurations. In addition, the rewritable luminescent paper and bioimaging applications were also achieved. These results demonstrated that the distinct molecular design could endow organic molecules with multifunctional properties and potential applications.

Dual state emissive pyrene-fused benzopyrazaacenes and their solvatochromic behaviour

This study investigates how molecular orientation and microstructure influence the photophysical and electronic properties of pyrene-fused azaacenes. Four substituted pyrene-fused benzopyrazaacene compounds were synthesized via a single step cyclo condensation of K-conjugated pyrene quinone building blocks with 3,4-diaminobenzophenone. The synthesized molecules were characterized using IR, NMR spectroscopy and HRMS analysis. Photophysical and electrochemical properties were studied to explore the impact of molecular orientation and microstructure on the properties of pyrene-fused azaacenes. Substitutions at the 2, 7-positions of the pyrene core significantly affected the photophysical properties while demonstrating moderate solubility. Notably, the compounds exhibited pronounced solvatochromic effect across various solvents. Furthermore, the additional incorporation of a carbonyl moiety adjacent to the core expanded pyrene at the K-region resulted in dual state emission, influencing solid state emission accompanied by robust thermal stability. Theoretical calculations were performed to gain insights into the energy levels of the compound and its molecular orientation using time dependent density functional theory (TD-DFT).

Precise synthesis of three-arm star polymethacrylates with high emission efficiency both in solution and in the solid state

Organic/polymeric fluorescent materials with bright emission both in solution and in the solid state have garnered growing interest in biological and optoelectronic fields. Herein, triphenylamine-derived boron ketoimine (TPA-BKI-3Br) was utilized as the initiator for atom transfer radical polymerization (ATRP) to prepare dual-state emission three-arm star polymethacrylates. Due to the intramolecular charge transfer (ICT) effect and highly distorted structure of the TPA-BKI unit, as well as the polymer arms constraining intramolecular motions, the resultant polymers displayed significant emission in solution. In the aggregated and solid states, the photophysical characteristics of the resultant polymethacrylates were notably impacted by the space charge transfer between the TPA-BKI unit and polymer chains. In addition, the TPA-BKI-based poly(2-(dimethylamino)ethyl methacrylate) (TPA-BKI-(PDMAEMA)3) exhibited fluorescence responses to temperature variations owing to the presence of dimethylamino group. This study presents an approach for the advancement of dual-state emission polymeric materials.

Aggregation-induced emission fluorogenic probes for wash-free imaging of lipid droplets in living cells

As essential subcellular organelles, lipid droplets (LDs) are involved in various the pathophysiological processes of metabolic diseases, including fatty liver and diabetes. Therefore, detecting LDs is conducive for studying the pathogeny and the early diagnosis of associated diseases. In this work, a series of fluorescent probes L1-L3 based on triphenylamine derivatives were designed and synthesized for tracking LDs in living cells. Due to the different terminal moieties of the three probes, L1 and L3 are aggregation-induced emission (AIE)-active, while L2 is a dual-state emission (DSE) molecule. In addition, confocal cell imaging experiments showed that probes L1-L3 specifically target intracellular LDs sites without the post washing. Importantly, probe L3 allows real-time monitoring of the dynamic processes and changes in the number of LDs. In summary, probe L3 is an ideal probe for studying LDs-related pathophysiological processes, and this work provides more ideas for the future design and synthesis of high-performance fluorescent probes for targeting LDs.

A novel bidirectionally operated chirped quantum-dot based semiconductor optical amplifier using a dual ground state spectrum

Bi-directionally operated amplifiers enabling efficient utilization of transmission wavelengths are promising candidates in densely integrated photonic circuits for future cost-effective, power-efficient optical networks. Here, we demonstrate, for the first time, a broadband semiconductor optical amplifier (SOA) based on a novel chirped multilayered quantum dot (QD) structure, which is suitable for bi-directional amplification via the dual ground state (GS) emission spectrum. The fabricated QD SOA has achieved a maximum 3-dB gain bandwidth of 50 nm while retaining on-chip gain above 20 dB at both GS wavelengths. Under an optimum pumping current of 280 mA, the bi-directionally operated QD SOA has shown around 10 dB receiver sensitivity improvement in ultra-high-speed 100 Gbaud non-return-to-zero and 53.125 Gbaud four-level pulse amplitude modulation data transmission systems.

Dual-state emission, mechanofluorochromism, and lipid droplet imaging of asymmetric D-π-A-D′-type triads

Dual-state emission (DSE) is an emerging phenomenon wherein organic luminescent molecules display bright emissions in both molecularly isolated and packed states, addressing the challenge associated with the traditional paradigm of dyes with mono-state emission. This study presents the design and synthesis of two unsymmetrical triads, TPCA and TPCT, featuring a D-π-A-D′ electronic structure by integrating phenothiazines, triphenylamines, and cyanostilbene. Photophysical assessments reveal that both molecules serve as robust DSEgens, exhibiting strong emissions in both solution and solid phases. TPCA displays ΦTHF 53.2% and Φsolids 43.2%, while TPCT exhibits ΦTHF 49.6% and Φsolids 37.5%. However, due to differences in molecular conformation and packing, they diverge in solid-state emission wavelengths and mechanofluorochromic behavior. In the solid state, TPCA emits strong red fluorescence, contrasting with TPCT, which emits orange fluorescence. Furthermore, TPCA demonstrates significant mechanofluorochromism (MFC), shifting from yellow to yellow-red upon mechanical grinding, while TPCT exhibits negligible MFC owing to conformational distinctions. As robust and low-toxic bioimaging agents, both TPCA and TPCT prove highly effective for lipid-droplet imaging studies. This research contributes valuable insights to the evolving field of DSE materials, elucidating the promising applications and mechanisms governing their versatile emission behaviors.

Functional-group-regulated stimuli-responsive banana-shaped α-cyanostilbene derivatives: Dual-state emission, AIEE, acidochromism and their applications in anti-counterfeiting, fingerprint recognition and OLEDs

The research of structure-property relationships is of great significance for exploring the luminescent mechanism, the design of functional materials with desired photoelectric properties and facilitating practical applications. In this paper, a series of cyanostilbene derivatives (TS-R) with different functional groups were synthesized by one step under mild conditions and characterized. Their photoelectric properties and structure-property relationships have been researched. The results indicate that TS-R have solution and solid dual-state emission (DSE) property, aggregation-induced emission enhancement (AIEE) effect, solvatochromism behavior and stimuli-responsive fluorescence characteristic for acid. The photoelectric properties can be changed by introducing different functional groups at the molecular same position of TS-R. The applications of TS-R were also investigated. The results indicate that TS-R can be used in fluorescent anti-counterfeiting, fingerprint recognition and light emitting diode (LED).

Dual-state emission and two-wavelength amplified spontaneous emission behaviors observed from symmetric dyes based on functionalized fluorene and benzotriazole units.

Structurally symmetric dyes using functionalized fluorenes and benzotriazole as the main building moieties have been synthesized and found to exhibit efficient dual-state emission (DSE) and interesting two-wavelength or dual amplified spontaneous emission (dual-ASE) behaviors in the solution phase, which may benefit the development of organic gain materials with dual-wavelength amplification.

Mechanistic insights into diversified photoluminescence behaviours of BF2 complexes of N-benzoyl 2-aminobenzothiazoles.

Many BF2 complexes of heteroaromatics are well known for their dual-state emission (DSE) properties. However, AIE and ACQ effects have also been observed in certain cases. To date, no rational explanations have been proposed for these uncommon photoluminescence (PL) behaviours. The current research prepared four BF2 complexes of N-benzoyl 2-aminobenzothiazoles with diversified photoluminescence (PL) properties as model compounds and utilized quantum chemical calculation tools to address this issue. Theoretical calculations revealed that the electron-donating groups (EDGs) at the para-position of the exocyclic phenyl ring exert significant influence on their ground-state electronic structures and vertical excitation features. Potential energy curve (PEC) analysis showed that the exocyclic phenyl ring and NMe2 could not function as effective rotors due to elevated energy barriers. Only the NPh2 of BFBB-3 could spontaneously rotate ∼60° to induce the formation of an emissive twisted intramolecular charge transfer (TICT) state. The two-channel model involving both vibronic relaxation and S0/S1 surface crossing revealed that the drastic narrowing of the S1/S0 energy gap in the region approaching minimun energy conical intersection (MECI) led to the generation of a dark state in BFBB-1. The small energy barrier to access the dark-state region makes the resulting fast internal conversion a competitive channel for excited-state deactivation. In contrast, the presence of EDGs in BFBB-2 and 4 inhibits this pathway, thereby resulting in intense fluorescence emissions in solution. In addition, crystallographic analysis illustrated that the F atoms perpendicular to the polyheterocycle promoted a slipped face-to-face packing mode and enhanced intermolecular interactions. The efficiencies of their solid-state emissions are mainly affected by the degree of π-π overlaps.

Long-wavelength dual-state luminescent naphthalimide derivatives for bio-imaging

A series of naphthalimide derivatives with long-wavelength emission, large Stokes shift, dual-state emission, and long emissive lifetime were obtained by constructing D–π–A structures applying in viscosity-responsive fluorescence lifetime imaging.