Large Stokes Shift Research Articles

Substituent-driven ESIPT in Chromeno-pyrroloquinoline probe for differentiating normal and cancer cells.

Despite significant advancements in the structural flexibility and functional diversity of fluorescent molecular sensors, the chromophores often require complex synthetic processes and are typically designed to perform only a specific function. Herein, we have demonstrated the unique features of fluorophores based on a fused coumarin-indole scaffold, which are synthetically available via a one-step reaction. Four fluorophores (ICH, ICEst, ICOMe, and ICNMe2) with varying substituents were synthesized and characterized. Subsequently, their response towards aggregation, solvent polarity, and viscosity was studied. Probe ICNMe2 exhibited aggregation-induced emission (AIE), while others displayed aggregation-caused quenching. The viscosity-sensitive nature of these fluorophores was evaluated using the Froster-Hoffman equation. ICNMe2 displayed the highest sensitivity towards polarity and polarity-independent viscosity. The plausible mechanism involved is intramolecular charge transfer (ICT) in probes ICH, ICEst, and ICOMe, whereas excited state intramolecular proton transfer (ESIPT) coupled ICT in the case of ICNMe2. Based on the distinct AIE-viscosity responses and large stokes shift (~175 nm), ICNMe2 was utilized for distinguishing normal (RAW 264.7) cells and cancer (A549) cells using confocal microscopy. Results demonstrated that ICNMe2 could effectively extend its photophysical activity in the cellular milieu with an enhanced emission in channel-1 (λem = 460-530 nm) for A549 compared to RAW 264.7 cells.

Near-infrared fluorescent probes based on naphthyridine derivatives for mitochondrial nucleic acid imaging.

Most current nucleic acid-responsive fluorescent probes are enhanced ones with short emission wavelengths. Therefore, the development of novel near-infrared, turn-on response nucleic acid fluorescent probes is of great significance. Herein, three cationic fluorescent dyes 1a-1c were synthesized by reacting naphthalidine salt with suitable aldehydes. These probes exhibited excellent photostability, maintaining over 95% of their absorption rate after 5 h of irradiation. Notably, probes 1a-1c exhibited an OFF-ON fluorescence response to DNA and RNA. The maximum emission wavelength could reach the near-infrared region (661-762 nm), with large Stokes shifts (153-222 nm) upon binding to DNA/RNA. The fluorescence intensity was enhanced 143 fold and 127 fold for 1b upon interaction with DNA and RNA, respectively. Co-staining and nucleic acid digestion assays showed that probes 1a-1c could target the mitochondria of fixed cells with low cytotoxicity. These findings may be useful for the early screening of genetic mutations related to mitochondrial diseases.

Less Is More: Donor Engineering of a Stable Molecular Dye for Bioimaging in the NIR-IIb Window.

Fluorescence molecular imaging aims to enhance clarity in the region of interest, particularly in the near-infrared IIb window (NIR-IIb, 1500-1700 nm). To achieve this, we developed a novel small-molecule dye, named DA-5, based on classic cyanine dyes (heptamethine or pentamethine is essential for wavelengths beyond 1000 nm). By reducing excessive polymethine to a single methine and disrupting symmetry to form an asymmetric donor-π-acceptor (D-π-A) architecture, we enhanced the donor's electron-donating capability, yielding emission at 1088 nm. DA-5 exhibits superior properties, including excellent chemo- and photostability, resistance against solvatochromism-caused quenching, and antiaggregation in aqueous solution. With a large Stokes shift (241 nm) and high brightness (321 M-1 cm-1), DA-5 enables high-performance imaging of the lymphatic system, intestinal vessels, whole-body angiography, and cerebral and hindlimb microvasculature in NIR-IIb. This molecular design strategy offers a promising platform for advancing in vivo biophotonics.

(2-Dimesitylboryl)phenyl]ethynyl-Substituted [2.2]Paracyclophane Exhibiting Circularly Polarized Luminescence in Both Solution and Solid-State.

Developing a new type of circularly polarized luminescent active small organic molecule that combines high fluorescence quantum yield and luminescence dissymmetric factor in both solution and solid state is highly challenging but promising. In this context, we designed and synthesized a unique triarylborane-based [2.2]paracyclophane derivative, m-BPhANPh2-Cp, in which an electron-accepting [(2-dimesitylboryl)phenyl]ethynyl group and an electron-donating N,N-diphenylamino group are introduced into two different benzene rings of [2.2]paracyclophane. Owing to the electronic effect of these two substituents, this compound can display charge-transfer emission with large Stokes shifts (∆υ = 4.23 - 8.20 × 103 cm-1) and fair quantum yields (ΦF = 0.15 - 0.37) in solutions. In addition, this compound can emit strong blue fluorescence in the solid state with quantum yields that are even much higher than in solution (ΦF up to 0.64 in powder and spin-coated film). Moreover, the enantiomeric forms of m-BPhANPh2-Cp can show strong CPL signals in both dilute solution and solid state with |glum|s up to 9.6 × 10-3 and 5.4 × 10-3, respectively. Thus, it is possible to achieve tunable CPL from blue to yellow in solution with high BCPLs ranging from 56.7 to 26.6 M-1 cm-1 and intense blue CPL combing high ΦF and |glum| in the solid state.

Elaborating H-bonding effect and excited state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzothiazole based D-π-A fluorescent dye.

2-(2-Hydroxyphenyl)benzothiazole (HBT) derivatives with donor-π-acceptor (D-π-A) structure have received extensive attention as a class of excited state intramolecular proton transfer (ESIPT) compounds in the fields of biochemistry and photochemistry. The effects of electron-donors (triphenylamine and anthracenyl), the position of substituents and solvent polarity on the fluorescence properties and ESIPT mechanisms of HBT derivatives were investigated through time-dependent density functional theory (TDDFT) calculations. Potential energy curves (PECs) and frontier molecular orbitals (FMOs) reveal that the introduction of the triphenylamine group on the benzene ring enhances intramolecular HB, thereby benefiting the ESIPT process. Analysis of their spectra reveals that P-TPA (para position for TPA) and M-TPA (meta position for TPA) are both excellent candidates for fluorescent dyes because of their large Stokes shifts. The PECs of four derivatives indicate that the ESIPT process of P-TPA in dimethyl sulfoxide (DMSO) solvent is the most likely to occur. The research revealed that both P-TPA and P-En (para positions for both TPA and En) can undergo a spontaneous transformation from the enol to the keto form in the S1 state. Furthermore, the ESIPT process was found to be enhanced with an increase in polarity. The energy barrier of P-TPA(N*) → P-TPA(K*) is 3.06 kcal mol-1 in the S1 state and its reversed energy barrier is 4.47 kcal mol-1. The para triphenylamine group could accelerate the ESIPT reactions, as it has a greater impact on the excited state intramolecular hydrogen bond (ESIHB) compared to meta-substitution of the triphenylamine group.

Design, Synthesis, and In Vivo Imaging of a Stable Xanthene-Based Dye with NIR-II Emission up to 1450 nm.

The development of long-wavelength near-infrared II (NIR-II, 900-1700 nm) dyes is highly desirable but challenging. To achieve both red-shifted absorption/emission and superior in vivo imaging capabilities, a donor-acceptor-donor (D-A-D) xanthene core was strategically modified by extending π-conjugated double bonds and enhancing electron-donating properties. Two dyes named VIX-1250 and VIX-1450 were synthesized and exhibited notably red-shifted absorption/emission peaks at 942/1250 and 1098/1450 nm, respectively. Among them, VIX-1450 demonstrated superior chemo- and photostability even at such long wavelengths. Fluorescent angiography using VIX-1450 micelles enabled high-clarity blood vessel imaging with a remarkable signal-to-noise ratio (SNR), underscoring that the dye's large Stokes shift (352 nm), good brightness (13 M-1 cm-1), and long wavelength served as key factors for high-quality in vivo biosensing. Additionally, VIX-1450 combined with ICG for dual-color imaging achieved near-zero optical cross talk, enabling different organ labeling. This study provides a new direction for the design of long-wavelength organic dyes.

Asymmetric Donor-Acceptor 2,7-Disubstituted Fluorenes and Their 9-Diazoderivatives: Synthesis, Optical Spectra and Photolysis.

In a search for dyes photoactivatable with visible light, fluorenes with substituents at positions 2 and 7 were prepared, and their absorption and emission spectra were studied. In particular, the synthesis route to 9-diazofluorenes with 2-(N,N-dialkylamino) and N-modified 7-(4-pyridyl) substituents was established. These compounds are initially non-fluorescent, undergo photolysis with UV or blue light, and-in non-polar media-provide orange- to red-emitting products with a large separation between absorption and emission bands. Irradiation of non-fluorescent 9-diazoderivative 20 in dioxane with the light of 365 nm or 470 nm was accompanied by strong fluorescence gain (10 to 20 times), orange-red emission, and a large Stokes shift of photoproducts, which structurally relate to fluorescent betaine 13 (model compound without diazo group). Photolysis of 20 in protic solvents (ROH = MeOH, H2O) provided clean transformation to C9-OR derivatives, though the emission gain in protic solvents was low.

Highly Efficient Luminescent Solar Concentrators Based on Capped Carbon Quantum Dots with Unity Quantum Yield

AbstractLuminescent solar concentrators (LSCs) can convert sunlight to clean energy by serving as large‐area collectors of sunlight. Benefiting from their large‐area, semi‐transparency, and lightweight characteristics, LSCs have gained a great of attention. However, their optical efficiency is limited by the low quantum yield (QY) and small Stokes shift of conventional photoluminescent materials. Carbon quantum dots (C‐dots) are promising alternatives, yet achieving both high QY and large Stokes shift has proven challenging. Here, a simple, controllable vacuum heating method is introduced to synthesize highly efficient C‐dots using a citric acid‐urea‐cyanuric acid‐CaCl2 system. The cyanuric acid‐capped C‐dots exhibit outstanding properties, including a QY of 94.3% in solution and 100% in a polymer matrix, a large Stokes shift of 0.64 eV, and exceptional photostability, making them ideal for LSC applications. Ultrafast transient absorption spectroscopy provides insights into their exciton dynamics. An LSC (25 cm2) based on these C‐dots achieves an optical efficiency of 13.82% ± 0.30%, while its attached photovoltaic cell attains a power conversion efficiency of 4.82% ± 0.10% under natural sunlight (80 mW cm−2), marking the highest performance reported for C‐dot‐based LSCs. These results highlight the potential of cyanuric acid‐capped C‐dots for advanced solid‐state lighting and energy conversion technologies.

Sensitive Fluorescent Probe for Al3+, Cr3+ and Fe3+: Application in Real Water Samples and Logic Gate.

Construction of single probes for simultaneous detection of common trivalent metal ions has attracted much attention due to higher efficiency in analysis and cost. A naphthalimide-based fluorescent probe K1 was synthesized for selective detection of Al3+, Cr3+ and Fe3+ ions. Fluorescence emission intensity at 534nm of probe K1 in DMSO/H2O (9:1, v/v) was significantly enhanced upon addition of Al3+, Cr3+ and Fe3+ ions while addition of other metal ions (Li+, Na+, K+, Ag+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+, Mn2+, Sr2+, Hg2+, Ca2+, Mg2+, Ce3+, Bi3+ and Au3+) did not bring about substantial change in fluorescence emission. The calculated detection limits were 0.32 µM, 0.81 µM, and 0.27 µM for Al3+, Cr3+, and Fe3+, respectively. Probe K1 displayed strong anti-interference ability, a large Stokes shift, rapid response, and applicability in a wide pH range for the simultaneous detection of Al3+, Cr3+ and Fe3+ in real water samples. Job's plot test showed that the stoichiometric ratio of the complexes formed between probe K1 and the trivalent metal ions was 1:1. The reversible application of probe K1 was realized by addition of Na2EDTA. A molecular logic gate was built based on the input-output information. This approach may provide a basis for highly selective and sensitive detection of common trivalent cations and for design of memory devices.

A Sensitive and Reusable Phenothiazine-Benzophenone Based Fluorescence Probe for Detecting Hypochlorite in Environmental and Biological Systems.

This study addresses the critical issue of irreversible oxidation in hypochlorite (ClO⁻) sensing by a phenothiazine-based compound, which typically leads to the probe's degradation and loss of functionality. We introduce a novel fluorescence probe, (2-(5-(10H-phenothiazin-10-yl)thiophen-2-yl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (PTH-BP), specifically designed to enhance ClO⁻ detection efficiency. PTH-BP exhibits strong aggregation-induced emission (AIE), emitting deep orange fluorescence at 620nm with a large Stokes shift of 195nm, and achieves an impressive detection limit of 1 nM in ACN/PBS buffer solutions. Job's plot analysis reveals a 1:1 binding stoichiometry, while fluorescence quenching occurs due to the oxidation of the phenothiazine sulfur to sulfoxide, confirmed by high-resolution mass spectrometry (HRMS). The probe's design improves stability, enabling effective real-time ClO⁻ monitoring and demonstrating reliable performance in electrochemical sensing. Furthermore, PTH-BP shows excellent imaging capabilities in HeLa cells, characterized by low toxicity and good permeability, making it a strong candidate for environmental, biological, and industrial applications. This breakthrough offers a robust and versatile approach to overcoming limitations in phenothiazine-based ClO⁻ sensing.

Strategic Modulation of Polarity and Viscosity Sensitivity of Bimane Molecular Rotor-Based Fluorophores for Imaging α-Synuclein.

Molecular rotor-based fluorophores (RBFs) that are target-selective and sensitive to both polarity and viscosity are valuable for diverse biological applications. Here, we have designed next-generation RBFs based on the underexplored bimane fluorophore through either changing in aryl substitution or varying π-linkages between the rotatable electron donors and acceptors to produce red-shifted fluorescence emissions with large Stokes shifts. RBFs exhibit a twisted intramolecular charge transfer mechanism that enables control of polarity and viscosity sensitivity, as well as target selectivity. These features enable their application in: (1) turn-on fluorescent detection of α-synuclein (αS) fibrils, a hallmark of Parkinson's disease (PD), including amplified fibrils from patient samples; (2) monitoring early misfolding and oligomer formation during αS aggregation; and (3) selective imaging of αS condensates formed by liquid-liquid phase separation (LLPS). In all three cases, we show that our probes have high levels of selectivity for αS versus other aggregating proteins. These properties enable one to study the interplay of αS and tau in amyloid aggregation and the mechanisms underlying neurodegenerative disorders.

An HPQ-based near-infrared dye for the detection of ClO- and accurate imaging of cells and mouse tumor sites in situ.

A new fluorescent probe (SWJT-32) with a large Stokes shift was designed and synthesized with 2-(2-hydroxyphenyl)-4(1H)-quinazolinone (HPQ) as the skeleton and N,N-dimethylthiocarbamate as the recognition site. It can detect hypochlorite ions (ClO-) through fluorescence spectroscopy based on the excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) mechanism. The probe has the advantages of strong diffusion resistance, good photostability and selectivity, and high imaging contrast, and can be used for the detection of ClO-. Meanwhile, due to its low toxicity and good biocompatibility in living cells, SWJT-32 can be used for the detection of endogenous and exogenous ClO- in HeLa cells as well as for long-term in vivo imaging in tumor mice.

A rhodamine based near-infrared fluorescent probe for selective detection of Cu2+ ions and its applications in bioimaging.

A novel near-infrared fluorescent probe TM2 based on a rhodamine-bearing framework was disclosed with a large Stokes shift (100 nm). TM2 exhibits highly selective recognition for Cu2+ in EtOH/H2O (1 : 1, v/v) solution with a low detection limit (2.3 μM) and a wide detection range (0-50 μM). Detection of Cu2+ is undisturbed at physiological pH levels of 5-9. This recognition mechanism is attributed to the formation of a 1 : 1 complex between TM2 and Cu2+, validated by Job's plot, 1H NMR titration, and LC-MS experiments. Moreover, the successful fluorescence imaging of Cu2+ both in vitro and in vivo was also accomplished.

Role of exciton delocalization in chiroptical properties of benzothiadiazole carbon nanohoops.

Development of chiral organic materials with a strong chiroptical response is crucial to advance technologies based on circularly polarized luminescence, enantioselective sensing, or unique optical signatures in anti-counterfeiting. The progress in the field is hampered by the lack of structure-property relationships that would help designing new chiral molecules. Here, we address this challenge by synthesis and investigation of two chiral macrocycles that integrate in their structure a pseudo-meta [2.2]paracyclophane with planar chirality and a highly fluorescent benzothiadiazole. Both compounds display remarkably red-shifted fluorescence with high quantum yields and large Stokes shifts. They differ in the extent of π-electron conjugation that allowed, for the first time, systematic examination of the effect of exciton delocalization on the absorption and luminescence of circularly polarized light. By a combination of steady-state spectroscopy and quantum chemical calculations, we constructed a unique structure-property relationship offering critical insights that will aid and abet the development of robust design guidelines for materials with strong electronic circular dichroism or circularly polarized luminescence of exceptional brightness.

Multicomponent synthesis of stereogenic-at-boron fluorophores (BOSPYR) from boronic acids, salicylaldehydes, and 2-formylpyrrole hydrazones.

This work describes one-step syntheses of various stereogenic-at-boron fluorochromes (BOSPYR) via multicomponent reactions involving readily accessible boronic acids, salicylaldehydes, and 2-formylpyrrole hydrazones. The dyes absorb and emit in the visible region of the electromagnetic radiation, and are characterized by large Stokes shifts (2850-4930 cm-1) with weak fluorescence emissions (Φfl: 1.5-9.1%). Notably, the dimmed fluorescence of BOSPYRs recovers upon transition to viscous media (21-fold for 1a). The representative compound 1a exhibits clear Cotton effects with dissymmetry factors of ca. |gabs| ∼ 1.9 × 10-3 in the visible region, indicating efficient asymmetry induction to the chromophore. The X-ray molecular structure of 1a shows that the chromophore deviates from planarity by 17.2°, which may contribute significantly to the inherent chirality of the fluorophore. A computational examination of excited states by time-dependent density functional theory (TD-DFT) identifies the emission mechanism as arising from a locally-excited (LE) state.

Theoretical study of excited state dynamics of a ratiometric fluorescent probe for detection of SO2 derivatives

Sulfur dioxide (SO2), a toxic air pollutant, can have harmful effects on human health when inhaled or when it forms bisulfite in the body. In the present work, a ratiometric fluorescent probe, 2-(2′-hydroxyphenyl)benzothiazole-3-ethyl-1,1,2-trimethyl-1H-benzo[e]indolium (HBT-EMBI), was selected to study the mechanism of SO2 derivatives detection. This study provides insights into the attributions of ratiometric fluorescence through hydrogen bond dynamics, electronic excitation properties, radiation rates, and excited state intramolecular proton transfer (ESIPT) processes using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) level. The results confirm that the large Stokes shifts and broad emission spectra of the HBT-EMBI probe are associated with its intramolecular charge transfer (ICT) characteristics and hydrogen bonding-driven ESIPT processes, respectively. After the addition reaction between the probe and HSO3−/SO32−, the conformational populations of HBT-EMBI-HSO3− transfer abnormally from enol configurations to more stable keto configurations, which leads to a distinguished change in the visible color and the ratiometric fluorescence signal, and is not due to the blockage of the ICT process of HBT-EMBI-HSO3−, as previously reported. This work provides a new perspective on the mechanism of detection of SO2 derivatives by ESIPT fluorescent probes.

Novel Nitrogen Hybrid F- Sensors Based on ESIPT Mechanism Achieving Super Low Detection Limits.

Two novel nitrogen hybrid fluorescent sensors based on the ESIPT mechanism were successfully synthesized for the detection of fluoride ions (F-), and they exhibit high sensitivity and selectivity with a fast response. The detection limits even reach the parts per billion level. With the addition of F-, both sensors showed a ratiometric fluorescence change with a large Stokes shift. According to the hydrogen-1 (1H) NMR titration, it was confirmed that the desilication reaction occurred between the sensors and F-. This work provides guidance for the subsequent development of F- fluorescence sensors.

Click-ready iridium(iii) complexes as versatile bioimaging probes for bioorthogonal metabolic labeling.

Herein, we report the synthesis, photophysical characterization and validation of iridium(iii)-polypyridine complexes functionalized for click chemistry and bioorthogonal chemistry, as well as their versatile applications as probes in bioimaging studies exploiting metabolic labeling. The designed dyes are conjugated to chemical reporters in a specific manner within cells by CuAAC ligation and display attractive photophysical properties in the UV-visible range. They are indeed highly photostable and emit in the far-red to near-IR region with long lifetimes and large Stokes shifts. We demonstrate that they can be efficiently used to monitor nascent intracellular sialylated glycoconjugates in bioorthogonal MOE studies with a varied panel of optical and non-optical techniques, namely conventional UV-vis laser scanning confocal microscopy (for routine purposes), UV-vis time-resolved luminescence imaging (for specificity and facilitated multiplexing with nano-environment sensitivity), synchrotron radiation based X-ray fluorescence nanoimaging (for high resolution, elemental mapping and quantification in situ) and inductively coupled plasma mass spectrometry (for routine quantification on cell populations with high statistical confidence). The synthesized Ir(iii) complexes were utilized in single labeling experiments, as well as in dual click-labeling experiments utilizing two distinct monosaccharide reporters relevant to the same metabolic pathway.

A new fluorescent probe with large Stokes shift for selective and sensitive detection of arginine

The development of fluorescent probes for prompt and accurate arginine (Arg) detection with high selectivity and sensitivity is in great demand due to the critical roles and implications of Arg for health. In this paper, a new coumarin-derived fluorescent probe, CL, was designed and synthesized. It was efficient for the rapid and specific detection of Arg in MeCN/H2O (6:4, v/v), with a low detection limit of 0.78 μM and a short response time of less than 10 s. Probe CL was stable at pH 3–10 and exhibited excellent anti-interference from competitive amino acids, including lysine, histidine, cysteine, homocysteine, glutathione, glycine, glutamic acid, valine, tyrosine, tryptophan, leucine, phenylalanine, aspartic acid and methionine. Density-functional theory (DFT) calculations investigated and verified the sensing mechanism. Considering that probe CL features multiple advantages, including high specificity, emission at a long wavelength of 642 nm with a massive Stokes shift of 272 nm, fast response and a broadly applicable pH range, this study provides a new idea for the development of susceptible and selective detection method for Arg.

PH-responsive supramolecular switch of a rationally designed dipyrroethene-based chromophore.

Herein, we present a strategy to access a novel class of pH-responsive, dual-state emissive (DSE), highly fluorescent pyrrole-based chromophores via diformylation of dipyrroethenes (DPE) followed by condensation with various aniline derivatives. The DPE-based chromophores exhibit a large Stokes shift and maintain good fluorescence quantum yields. Remarkably, these chromophores demonstrate reversible colourimetric changes and a fluorometric 'on-off-on' switch in response to pH variations. Various spectroscopic techniques, optical microscopy, X-ray crystallography, and computational studies revealed that the synthesized molecules adopt a two-dimensional conformation due to the presence of strong π⋯π stacking and hydrogen bonding interactions, allowing them to function as flexible molecular hosts. Under acidic conditions, selective protonation of imine bonds and subsequent complexation with the counter anion enhance the host-guest interactions, resulting in a stable three-dimensional supramolecular structure. Notably, the reversibility of these molecules under basic conditions showcases the robustness and potential applications of these chromophores in various fields, ranging from the design of finely tuned pH-responsive degradable polymers to self-healing materials, as well as sensing and molecular devices.