Shift Of Emission Wavelength Research Articles

Donor–Acceptor Type Solvatochromic Flavonoid Materials Fluorphores for Polarity Sensing and Real‐Time Temperature Monitoring

AbstractElectron donor–acceptor (D–A) molecules are emerging tools for designing sensitive luminogens, attracting significant research attention. However, due to poor quantum yields under certain conditions, current D–A fluorophores often suffer from fluorescence quenching in practical applications. Developing new D–A dyes and functional composites is crucial for expanding their applications. Here, a novel donor–acceptor type flavonoid dye molecule, namely “AFL”, exhibiting both polarity‐dependent fluorescence emission wavelength shift and viscosity‐dependent intensity change, for polarity measurement and temperature sensing is designed and synthesized. Because the intramolecular charge transfer (ICT) can be enhanced by a decrease of excited state energy caused in high‐polarity organic solvents, AFL undergoes fluorescence emission wavelength shift that shows fluorescence color response to solvents of different polarities and hence differentiates between them. Moreover, the actual temperature can be monitored by the as‐designed AFL@tetradecanoic acid (AFL@TA) sensor. By combining with TA, viscosity sensitively changes upon the temperature change of insoluble composites, thus realizing the fluorescence intensity response to temperature. Remarkable recyclable performance and satisfactory mechanical properties are integrated. This study provides a promising approach to developing a new D–A fluorescent probe and furnishes perspectives on the potential of such D–A type flavonoid material in stimuli‐responsive systems with a focus on visualization sensing technology.

A Novel Near-Infrared Tricyanofuran-Based Fluorophore Probe for Polarity Detection and LD Imaging

In this paper, LD-TCF, a targeting probe for lipid droplets (LDs) with a near-infrared emission wavelength and large Stokes shift, was fabricated for polarity detection by assembling a donor–π–acceptor (D–π–A) molecule with typical twisted intramolecular charge transfer (TICT) characteristics. Surprisingly, the fluorescence emission wavelength of the newly constructed probe LD-TCF was stretched to 703 nm, and the Stokes shift was amplified to 126 nm. Furthermore, LD-TCF could specifically answer the change in polarity efficiently and did not experience interference from other biologically active materials. Importantly, LD-TCF exhibited the ability to target lipid droplets, providing valuable insights for the early diagnosis and tracking of pathophysiological processes underlying LD polarity.

Inverted V-shaped size-dependent emission wavelength shift in InGaN micro-LEDs with size down to 1 μm

The size-dependent emission wavelength shift of micro-scale light emitting diodes (micro-LEDs) has been frequently reported in recent publications, but its underlying physical mechanism has not yet been thoroughly elucidated. Here, we fabricate and characterize the red, green, and blue InGaN micro-LED mesas with different diameters down to 1 μm. As the size decreases, all the samples of different colors show an inverted V-shaped photoluminescence wavelength variation trend, first a red shift and then a blue shift, and the shifting range is larger for samples with longer wavelengths. Micro-Raman spectrum confirms that the stress was significantly released after scaling down the size from epitaxial wafer to 1 μm. The theoretical simulations show that the red and blue shifts are, respectively, attributed to the bandgap narrowing and the weakening of the quantum-confined Stark effect caused by strain relaxation, which dominate successively.

Surface State-Based panchromatic luminescent carbon dots

Carbon dots have shown a broad application prospect in the fields of sensing and detection, biological imaging, and optoelectronic devices. However, it is still challenging to adopt a simple and green synthesis route and to develop new precursor systems to prepare full-color luminescent carbon dots. This study proposes a mechanism for fine regulation of carbon dot fluorescence spectra based on surface states of CN, COC, and OH, among which CN play a major role in long wavelength emission while COC and OH are responsible for the blue shift of emission wavelength. Using 4,4-bipyridine and p-phenylenediamine as precursors in safe and environmentally friendly glycol and water as solvents for the first time, the fine spectral carbon dots with full spectrum luminescence from purple (441 nm) to red (627 nm) were successfully synthesized by simply changing the composition of the reaction solvent and using a short reaction time. Compared with other reports on regulating polychromatic carbon dots, our method is more refined and has a wider distribution of luminescent colors. In addition, the obtained carbon dots based on such surface state luminescence mechanism have shown good application prospects in specific detection of Fe3+and cell labeling.

Coordination Synergistic-Induced J-Aggregation Enhanced Fluorescent Performance of HBT-Excimers and Imaging Applications.

Developing a novel strategy to improve the optical performances of fluorescent probes is a vital factor in elevating its practical application; viz., novel biocompatible fluorescent probes with excellent multifunctions exhibited unparalleled advantages in probing functions of intracellular molecules to elucidate intracellular events in living systems. Herein, we have successfully constructed a new strategy that aggregation and coordination synergistically induce (2-hydroxylphenyl-benzothiazole) HBT derivatives to form excimers with large red-shifted fluorescence and application for insight into stress-response zinc fluctuations in living systems. We have synthesized four HBT-based derivatives and deeply investigated the response mechanism by fluorescent spectral studies, demonstrating that probes 3 and 4 showcased large red shifts in emission wavelength due to J-aggregation. More interestingly, the fluorescence of probe 4 was significantly enhanced in the presence of a zinc ion, suggesting that zinc coordination synergistically induced J-aggregation. Probe 4 was successfully applied to image zinc fluctuations in different models of living systems, proving that this probe is a powerful tool to unveil the relationship between invasive stress and diseases by monitoring endogenous zinc fluctuations.

New graphene oxide doped polymer dispersed liquid crystal nanocomposites targeted to eco-friendly and energy-efficient smart windows

Graphene oxide-polymer dispersed liquid crystal (GO-PDLC) composites are proposed as a solution for energy-efficient switchable windows. These composites were prepared by incorporating varying concentrations of graphene oxide (GO) into a mixture of nematic liquid crystal (E7) and a UV–Vis curable resin using the polymerization-induced phase separation technique. The results indicate that the dispersion of GO at an optimum concentration of 0.005 wt% significantly affects the morphology, phase transition temperatures, and electro-optic properties of polymer dispersed liquid crystal (PDLC). In particular, the GO-PDLC composites exhibit a transition from an opaque to a transparent state at a remarkably low voltage (∼11.5 V) compared to pure PDLC cell. Dielectric analysis reveals that adding GO increases the permittivity, conductivity, and dielectric strength of PDLC composites. Moreover, the Cole-Cole plot indicates a non-Debye type relaxation in a higher frequency region. Furthermore, a blue shift in emission wavelength and enhanced photoluminescence intensity suggest alterations in electronic transitions within the composites. This comprehensive study provides valuable insights into optimizing the properties of PDLCs through the dispersion of GO, thereby offering promising prospects for their utilization in various optoelectronic applications.

Constructing soybean protein isolate /bacterial cellulose co-assemblies by pH shifting treatment: Molecular conformation and physicochemical properties

The study elucidates that the pH shifting treatment unfolds the conformation of soybean protein isolate (SPI), enabling it to intertwine with bacterial cellulose (BC) and form SPI/BC co-assemblies. Results from intrinsic fluorescence spectroscopy and surface hydrophobicity indicate that the SPI with pH shifting treatment shows a notable blue shift in maximum emission wavelength and increased surface hydrophobicity. It demonstrates that pH shifting treatment facilitates the unfolding of SPI's molecular conformation, promoting its entanglement with high aspect ratio BC. Particle size distribution and microstructural analysis further demonstrate that the pH shifting treatment facilitates the formation of SPI/BC co-assemblies. Evaluation of processing properties reveals that the SPI/BC co-assemblies exhibited exceptional gel and emulsification properties, with gel strength and emulsifying activity respectively six and two times higher than natural SPI. This enhancement is attributed to the thickening properties of BC with a high aspect ratio and the superior hydrophobicity of SPI in its molten globule state.

Enhancement of non-covalent interaction between soy protein isolate and quercetin by sodium alginate

Effects of sodium alginate (SA) on the non-covalent interaction between soybean protein isolate (SPI) and quercetin (Que) were investigated by multispectral technology, molecular docking and dynamics simulation technology. Structural alterations of the binary complexes were observed after SA addition, characterized by a red shift of maximum fluorescence emission wavelength. The introduction of 0.1% (w/v) SA led to a reduction of 12.3% in the α-helix and β-sheet structures, accompanied by 12.6% increase in the β-turn and random coil conformations. The binding of SA to SPI provided electrostatic interactions and facilitated the subsequent binding of SPI to Que. Molecular docking confirmed that hydrophobic interactions and electrostatic interactions were also the main driving force. Molecular dynamics simulation emphasized that the ternary complexes with SA exhibited greater stability compared to the binary ones. The foaming and emulsifying properties of SPI-Que complexes were enhanced by 33.76% and 68.28%, respectively, due to the addition of SA.

Pretheranostic agents with extraordinaryNIRF/photoacoustic imaging performanceand photothermal oncotherapy efficacy

Cervical cancer, the most common gynecological malignancy, significantly and adversely affects women's physical health and well-being. Traditional surgical interventions and chemotherapy, while potentially effective, often entail serious side effects that have led to an urgent need for novel therapeutic methods. Photothermal therapy (PTT) has emerged as a promising approach due to its ability to minimize damage to healthy tissue. Connecting a biothiol detection group to PTT-sensitive molecules can improve tumor targeting and further minimize potential side effects. In this study, we developed a near-infrared fluorescence (NIRF)/photoacoustic (PA) dual-mode probe, S-NBD, which demonstrated robust PTT performance. This innovative probe is capable of activating NIRF/PA signals to enable the detection of biothiols with high emission wavelength (838 nm) and large Stokes shift (178 nm), allowing for in vivo monitoring of cancer cells. Additionally, the probe achieved an outstanding photothermal conversion efficiency of 67.1%. The application of laser irradiation (660 nm, 1.0 W/cm2, 5 min) was able to achieve complete tumor ablation without recurrence. In summary, this seminal study presents a pioneering NIRF/PA dual-mode dicyanoisophorone-based probe for biothiol imaging, incorporating features from PTT for the first time. This pioneering approach achieves the dual objectives of improving tumor diagnosis and treatment.

A Near-Infrared Fluorescent Dye with Tunable Emission Wavelength and Stokes Shift as a High-Sensitivity Cysteine Nanoprobe for Monitoring Ischemic Stroke.

Sulfur-substituted dicyanomethylene-4H-chromene (DCM) derivatives based on the intramolecular charge transfer (ICT) mechanism were designed as near-infrared (NIR) fluorescent dyes. Using the Knoevenagel condensation method, the S-DCM-OH(835) fluorescence dye was synthesized, which had an emission wavelength exceeding 800 nm and 220 nm of a Stokes shift. Compared to commercial ICG, S-DCM-OH(835) was not only synchronized in emission wavelength but also far superior in Stokes shifts. These advantages made the design of S-DCM-NIR(835) based on this dye potentially valuable for biological applications. Based on this chemical structure, a fluorescent S-DCM-NIR(835) nanoprobe with a mean diameter of 17.69 nm was fabricated as the NIR imaging nanoprobe. Results showed that the nanoprobe maintained the high-specificity identification of cysteine (Cys) via the Michael addition reaction, with the detection limitation of 0.11 μM endogenous Cys. More importantly, in an ischemic stroke mouse model, the S-DCM-NIR(835) nanoprobe could monitor the Cys concentration change at stroke lesion due to the disruption of Cys metabolism under the ischemic stroke condition. Such a S-DCM-NIR(835) nanoprobe could not only differentiate the severity of the ischemic stroke using response time but also quantify the concentration of Cys in real-time in vivo.

Tunable emission color from lead-free zero-dimensional Mn2+-doped Cs3InCl6 single crystals

In recent years, the magneto-optical properties of zero-dimensional metal halides have attracted widespread interest. In this study, we employed a vacuum solid-state reaction method to synthesize zero-dimensional, lead-free, and all-inorganic Cs3InCl6 single crystals (SCs). In addition to the blue emission of self-trapped excitons (STEs) inherent to pristine Cs3InCl6, the strategic doping with Mn2+ ions not only facilitates multicolor emissions but also significantly boosts the photoluminescence quantum yield (PLQY) from a modest 1.21 % to an impressive 32.18 %. We carried out an exhaustive investigation into the fundamental mechanisms responsible for these multicolor emissions and the intricate compositional transitions that ensue. Furthermore, the pronounced correlation between temperature-dependent photoluminescence (PL) and magnetic characteristics unveiled the genesis of ferromagnetism within both the pristine and Cs3InCl6: xMn2+ samples. The doping-induced modifications in magnetic behavior furnish a coherent explanation for the anomalous inverse temperature dependence emission wavelength shift. Our research highlights the adjustable PL and magnetic attributes of Mn2+ doped Cs3InCl6, yielding invaluable insights that are poised to advance its application in the next wave of optoelectronic and magnetic technologies.

Versatile aggregation induced emissive molecular probes incorporating different donor/acceptor groups for tunable multiple color fluorescence

Excited state intramolecular proton transfer (ESIPT) and aggregation induced emission active multicolour fluorescent probes for bioimaging applications has grown popularly in recent years. Herein, we report a series of different donor/acceptor units (Cl, NO2 and O–CH3) bearing anthracene-salicylaldehyde based fluorescent probes and their antibacterial activity and fluorescence imaging of E. Coli bacteria and zebrafish embryos. All the compounds (ASA1, ASA2, ASA3 and ASA4) synthesized via facile one pot condensation reaction of anthracene hydrazide with Salicylaldehyde, 5-Chlorosalicylaldehyde, 5-Nitrosalicylaldehyde, 5-methoxysalicylaldehyde and characterized using all the possible spectroscopic techniques. The noteworthy tuneable emission wavelength shifts from 471 nm to 625 nm and ESIPT characteristics of the compounds were demonstrated through photophysical experiments and single crystal X-ray diffraction analysis. All the experimental results were completely analyzed theoretically on the ground as well as the excited state using density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations. Compounds ASA1-ASA4 showed fascinating different colour fluorescent (Green, Yellow and Orange) aggregation induced emission features in the THF-H2O mixture. AIE characteristics of ASA1, ASA2, ASA3 and ASA4 were recognized using absorption, emission, fluorescence quantum yield (Φ), DLS and SEM analysis. ASA1, ASA2, ASA3 and ASA4 showed excellent antibacterial activity and ROS generation against E. Coli bacteria. Further, owing to their multicolour fluorescent property all the compounds successfully applied for fluorescent imaging in E. Coli bacteria and live zebrafish embryos.

Silver-doped CdSe magic-sized nanocrystals.

Magic-sized nanocrystals (MSNCs) grow via jumps between very specific sizes. This discrete growth is a possible avenue toward monodisperse nanomaterials that are completely identical in size and shape. In spite of this potential, MSNCs have seen limited study and application due to their poor optical properties. Specifically, MSNCs are limited in their range of emission wavelengths and commonly exhibit poor photoluminescence quantum yields (PLQYs). Here, we report silver doping of CdSe MSNCs as a strategy to improve the optical properties of MSNCs. Silver doping leads to controllable shifts in emission wavelength and significant increases in MSNC PLQYs. These results suggest that doped MSNCs are interesting candidates for displays or luminescent solar concentrators. Finally, we demonstrate that the doping process does not affect the magic size of our MSNCs, allowing further photophysical study of this class of nanomaterial.

Difluoroboron Complexes Based on Benzimidazole-Phenolates as Blue Emitters.

Novel four-coordinated boron complexes (1-5) were synthesized via a reaction between BF3·CH3OH and benzimidazole-phenolate ligands (L1-L5), which are N,O-donors. These complexes exhibit intense blue emission in the solution and solid states accompanied by notable fluorescence quantum yields (ΦF). The study of the structure-property relation, through theoretical and experimental approaches, revealed a distinctive trend where compounds incorporating electron-donating substituents (methyl and ethoxy groups) in the phenolate moiety manifest shifts in emission wavelengths across the blue spectrum, concomitant with an increase in ΦF. Furthermore, the incorporation of an aromatic ring into the benzimidazole moiety considerably intensifies the rate of radiative relaxation from excited states. Notably, in the solid phase, either as a crystalline powder or loaded into polymer films, these modified complexes maintain or even surpass ΦF values observed in molecular solutions, ranging from 0.18 to 0.57, depending on the substitution. This characteristic makes these compounds attractive for applications in optoelectronics. All of the compounds were characterized using 1H, 13C, 11B, and 19F NMR, elemental analysis, and the molecular structures were corroborated through single-crystal X-ray diffraction analysis. Computational calculations via time-dependent density functional theory further elucidate the tunability of optical bandgaps through group substitution on ligands, aligning well with experimental observations.

Auxochrome Dimethyl-Dihydroacridine Improves Fluorophores for Prolonged Live-Cell Super-Resolution Imaging.

Superior photostability, minimal phototoxicity, red-shifted absorption/emission wavelengths, high brightness, and an enlarged Stokes shift are essential characteristics of top-tier organic fluorophores, particularly for long-lasting super-resolution imaging in live cells (e.g., via stimulated emission depletion (STED) nanoscopy). However, few existing fluorophores possess all of these properties. In this study, we demonstrate a general approach for simultaneously enhancing these parameters through the introduction of 9,9-dimethyl-9,10-dihydroacridine (DMA) as an electron-donating auxochrome. DMA not only induces red shifts in emission wavelengths but also suppresses photooxidative reactions and prevents the formation of triplet states in DMA-based fluorophores, greatly improving photostability and remarkably minimizing phototoxicity. Moreover, the DMA group enhances the fluorophores' brightness and enlarges the Stokes shift. Importantly, the "universal" benefits of attaching the DMA auxochrome have been exemplified in various fluorophores including rhodamines, difluoride-boron complexes, and coumarin derivatives. The resulting fluorophores successfully enabled the STED imaging of organelles and HaloTag-labeled membrane proteins.

Solvent-Dependent Emissions Properties of a Model Aurone Enable Use in Biological Applications.

Fluorophores are powerful visualization tools and the development of novel small organic fluorophores are in great demand. Small organic fluorophores have been derived from the aurone skeleton, 2-benzylidenebenzofuran-3(2H)-one. In this study, we have utilized a model aurone derivative with a methoxy group at the 3' position and a hydroxyl group at the 4' position, termed vanillin aurone, to develop a foundational understanding of structural factors impacting aurone fluorescence properties. The fluorescent behaviors of the model aurone were characterized in solvent environments differing in relative polarity and dielectric constant. These data suggested that hydrogen bonding or electrostatic interactions between excited state aurone and solvent directly impact emissions properties such as peak emission wavelength, emission intensity, and Stokes shift. Time-dependent Density Functional Theory (TD-DFT) model calculations suggest that quenched aurone emissions observed in water are a consequence of stabilization of a twisted excited state conformation that disrupts conjugation. In contrast, the calculations indicate that low polarity solvents such as toluene or acetone stabilize a brightly fluorescent planar state. Based on this, additional experiments were performed to demonstrate use as a turn-on probe in an aqueous environment in response to conditions leading to planar excited state stabilization. Vanillin aurone was observed to bind to a model ATP binding protein, YME1L, leading to enhanced emissions intensities with a dissociation equilibrium constant equal to ~ 30 µM. Separately, the aurone was observed to be cell permeable with significant toxicity at doses exceeding 6.25 µM. Taken together, these results suggest that aurones may be broadly useful as turn-on probes in aqueous environments that promote either a change in relative solvent polarity or through direct stabilization of a planar excited state through macromolecular binding.

Fluorescent 2-carbonyl carbazole ketones: Photophysical properties, molecular structure and selective detection of Fe3+ ion

Owing to the diverse implication of carbazole scaffolds in medicinal chemistry, photoelectronic materials and chromophores, the molecules containing the carbazole motif have attracted significant attention over the years. In this work, the vibronic contributions to carbazole structures could facilely change the solvatochromic effect, absorption wavelength, emission wavelength, and Stokes shifts of six 2-carbonyl carbazole ketones fluorophores. Among them, the structure of 1-(1-methyl-9H-carbazol-2-yl)ethanone (3a) were confirmed from single crystal XRD studies. The ratiometric detection of Fe(III) ion of 2-carbonyl carbazole ketone 3a were investigated. Furthermore, it was speculated that chemosensor 3a toward the recognition of Fe3+ cation was dependent on its rigid structure and good coplanarity of the conjugated system, strong intramolecular charge-transfer of 3a.

Gelation behavior and solvent-, thermo, acid-fluorochromic behavior of acylhydrazone derivative

Recently, there has been significant interest in multi-functional organic materials due to their unique properties and potential applications. One such material is PAD, an acyl-hydrazone derivative substituted with –OH and a triphenylamine group. PAD is capable of forming stable organogels in various solvents such as benzene, chlorobenzene, dichloromethane, and 1,2-dichloroethane. The organogels formed in benzene, dichloromethane, and 1,2-dichloroethane exhibit gelation-induced emission enhancement (GIEE) behavior, while not very obvious for chlorobenzene organogel. Additionally, PAD displays fluorescence switching behavior in response to changes in solvent and temperature. PAD-A emits blue fluorescence around 460 nm, while PAD-T emits green fluorescence at 485 nm. Interestingly, when PAD-T is annealed at 170 °C for 15 min, the fluorescence color changes from green to blue, and the emission wavelength shifts from 485 nm to 444 nm. Furthermore, regardless of whether it is in a solid, organogel, or solution form, PAD exhibits fluorescence quenching properties when exposed to acid (TFA) due to the protonation effect.

High-Sensitivity Detection of Changes in Local Refractive Index and Absorption by Analyzing WGM Microlaser Emission via a 2D Dispersion Spectrometer.

Microlasers have been widely used in biosensing applications because of their high sensitivity to changes in local conditions. However, in most applications, the sensitivity limit is not dictated by the microlaser line width but rather by the much worse spectral resolution of the detection system, typically a grating spectrometer. To address this issue, we built and characterized a two-dimensional (2D) dispersion spectrometer with a virtually imaged phase array etalon and a diffraction grating. The spectrometer can analyze microlaser emission with a spectral resolution of better than 0.300 pm, which enables high-precision measurements of spectral shifts in laser peak emission wavelength and sufficient resolution to detect changes in peak line width. Using commercial fluorescent microspheres as the microlasers, the 2D dispersion spectrometer demonstrated a detection limit for the refractive index change of a liquid medium of 1.37 × 10-5 RIU and a detection limit for absorption changes of less than 0.02 cm-1.

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