Photoinduced intramolecular charge transfer of sodium 4-(N,N-dimethylamino) benzenesulfonate

A new dual fluorescent N,N-dimethylaniline derivative, sodium 4-(N,N-dimethylamino)-benzenesulfonate (SDMAS), is reported. In SDMAS, the electron acceptor is linked to the phenyl ring via a sulfur atom at the para-position of the electron donor. It was found that SDMAS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as formamide, methanol and acetonitrile. In organic solvents only a single-band emission at ca.360 nm was observed in the short wavelength region. The dual fluorescence of SDMAS in water was found at 365 and 475 nm, respectively. Introduction of organic solvent such as ethanol, acetonitrile, and 1,4-dioxane into aqueous solution of SDMAS leads to blue-shift and quenching of the long-wavelength emission. Measurements of steady-state and picosecond time-resolved fluorescence indicate that the long wavelength fluorescence is emitted from a charge transfer (CT) state that is populated from the locally excited (LE) state, with the latter giving off the     

Theoretical investigation on dual fluorescence and intramolecular charge transfer of 5-phenyl-5H-phenanthridin-6-one

Quantum-chemical calculations with the time-dependent density function theory (TDDFT) have been carried out for 5-phenyl-5H-phenanthridin-6-one (PP). For this molecule, dual fluorescence and in- tramolecular charge transfer (ICT) were experimentally observed. The B3LYP functional with 6-311 G (2d, p) basis set has been used for the theoretical calculations. The solvent effects have been described within the polarizable continuum model (PCM). Ground-state geometry optimization reveals that the phenyl/phenanthridinone dihedral angle equals 90.0°, a nearly perpendicular structure. Vertical ab- sorption energy calculations characterize the lower singlet excited states both in gas phase and in solvents. It can be found that the lower excited states have locally excitation (LE) feature. Through constructing the potential energy curves of both isolated and solvated systems describing the LE→ICT reaction and fluorescence emission, we obtain the enthalpy difference ΔH between the LE and ICT states, energy barrier Ea, and energy difference δEFC, indicating the structural changes taking place during the ICT reaction. Potential curve and calculated emission energies for both isolated and sol- vated systems show a dual fluorescence phenomenon, consisting of a LE emission band and a red-shifted ICT band. Our calculations including the solvent effects indicate that the dual fluorescence is brought about by the change in molecular structure connected with the planarization of the twisted N-phenylphenanthridinone during the ICT reaction.     

Quantum chemical study on excited states and charge transfer of oxazolo[4,5-b]-pyridine derivatives

The excitedstate intramolecular charge transfer of four oxazolo[4,5-b]pyridine derivatives with different electron donating and electron withdrawing groups was investigated using the time-dependent density functional theory. The vertical excitation energies and the electronic structures were explored. Their distinct properties of absorption and fluorescence spectra in solvent phase were explained according to the electronic coupling matrix elements calculated by the Mulliken-Hush theory. The sub-stituent on the oxazolo[4,5-b]pyridines will remarkably change their spectra properties and increase the first excited-state dipole moments. The effect of protonation on the absorption and fluorescence spectra was also investigated systematically. Our study suggests that the present method is feasible to explain charge transfer excitation and predict the properties of absorption and emission spectra in the studied systems.     

Gold Nanoclusters Templated by Poly-cytosine DNA as Fluorescent Probes for Selective and Sensitive Detection of Thiocyanate

Gold nanoclusters(AuNCs) were prepared in the presence of the nucleobases of poly-cytosine DNAs in this paper. We have demonstrated tliat the fluorescence of the AuNCs is quenched by thiocyanate(SCN^-) through the interaction between SCN^- and gold atoms. AuNCs can receive energy from nucleobases to boost their emission intensity, while in the presence of SCN^-, they coordinate with Au atoms and influence the energy transfer between the nucleobases and AuNCs, leading to the fluorescence quenching. The decreased fluorescence intensity was in proportion to the concentration of SCN^- in the range of 8.0×10^-7-1.5×10^-5 mol/L with a limit of detection of 4.2×10^-7 mol/L(3σ). We further validated the practice of this probe througli the detection of SCbT in natural water samples.     

Probing the effects of external species on poly(acrylate acid) chain dynamics by using cationic AIE-active fluorophore

We report here our results on the investigation of the chain dynamics of poly(acrylic acid) in aqueous solution. The concentration of poly(acrylic acid) was approximately 3.8×10~(-4) mol/L, two orders of magnitude higher than that reported in the literature. The p H value of the solution was 3.9, and the hydrogen bonds between the intrinsic and ionized carboxylic acid groups formed dynamic networks, which captured aggregation-induced emission-active molecules(a tetra-quaternary ammonium modified tetraphenylethene derivative) inside the polymer coils and induced fluorescence emission. The hydrogen bonds can be classified as intra- or intermolecular; both can be probed based on the emission change of the tetra-quaternary ammonium modified tetraphenylethene probes. The effects of different external stimuli on the polymer chain dynamics were investigated using different metal cations(including Na~+, Li~+, Zn~(2+), Ni~(2+), Ca~(2+), and Co~(2+)), different cation concentrations(1×10~(-6) to 4×10~(-4) mol/L), different poly(acrylic acid) molecular weights(5, 240, and 450 k Da), and different copolymers. The experimental results indicate that the long poly(acrylic acid) chains(high molecular weight) tend to form dense globular coils and exclude the probe molecules outside, which are robust and unsusceptible to water-soluble metal cations. However, the shorter poly(acrylic acid) chains tend to form intermolecular hydrogen bonds, which are helpful in capturing more probe molecules inside the networks, thus inducing stronger emission. Because of the dual functions of forming hydrogen bonds with carboxylic groups and acting as an acceptor of protons from the carboxylic acid group to form cationic species, copolymerization with acrylate amide [poly(acrylic acid)-co-poly(acrylamide)] can greatly affect the chain dynamics of poly(acrylic acid) segments, which is reflected by the drastically decreased emission intensity from the fluorescent probes.     

Synthesis of a fluorescent probe based on naphthalimide derivative for simultaneous detecting of NO and pH in bioimagingEI北大核心CSCD

A new type of fluorescent probe Na-pHNO was synthesized for the simultaneous detection of NO and pH based on naphthalimide derivative. The probe had good fluorescence property in mixture solution of 99% phosphate buffer solution（PBS）and 1% dimethyl sulfoxide（DMSO）solution. It can produce a yellow-green emission peak at 544 nm,and the fluorescence intensity can be enhanced with the increase of NO concentration or the decrease of pH. The probe Na-pHNO displayed good selectivity,high sensitivity,and strong anti-interference towards NO,exhibiting good fluorescence reversibility at pH 5.5-8.5. The spectral studies showed that the probe Na-pHNO exhibited weak fluorescence due to a dual photoinduced electron transfer（PET）effect. After interacting with NO or pH,the dual PET inhibitory effect occurred,and the fluorescence intensity was significantly enhanced. The fluorescence imaging of probe Na-pHNO in HeLa cells showed that it could realize the visual monitoring of the changes of intracellular pH and NO concentration. The probe has been successfully applied to fluorescence imaging of Caenorhabditis elegans. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Effects of Hydrogen-bonding Interaction and Polarity on Emission Spectrum of Naphthalene-Triethylamine in Mixed Solvent

The effects of the protic and aprotic polar solvents on the emission spectrum of the naphthalene-triethyl-amine system in THF were studied under conditions of steady-state illumination. The fluorescence spectrum of the naphthalene-triethylamine system consists of two emission bands, the fluorescence band of naphthalene (band A, 329 nm) and the emission band of the exciplex(band B, 468 nm). The intensities of both the emission bands decrease with increasing the solvent polarity. The intensity of band B also decreases due to the hy-drogen-bonding interaction between triethylamine and protic solvent, while that of band A increases. It is thus suggested that the quenching of naphthalene fluorescence by triethylamine in THF occurs through the charge transfer and electron transfer reactions. The spectral changes upon the increase of solvent polarity can be explained by the dependences of the equilibrium constant between exciplex and ion-pair and the rate constant for the electron transfer reaction from triethyl.amine to the excited naphthalene on the rel.ative permittivity of solvent. It is shown that the formation of intermolecular hydrogen-bonding between triethylamine and protic solvent suppresses the quenching reaction by the decrease in free amine. Acetonitrile has only a polar effect and trichloroacetic acid only a hydrogen-bonding(or protonation) effect, while alcohols have both the effects. The effects of alcohols could be separated into the effects of solvent polarity and intermolecular hy-drogen-bonding interaction quantitatively.     

STUDY ON THE PROTONATION MECHANISM OF 2,6-DIMETHYL NAPHTHALENE DICARBOXYLATE

By the study of absorption and fluorescence spectra and the lifetime of fluorescence at room and low temperatures of 2,6-dimethyl naphthalene dicarboxylate (DMN) in different concentrations of sulfuric acid, different interactions between molecules of DMN and sulfuric acid have been observed. These interactions have been revealed by the absorption spectra of charge transfer complex in the ground state, emission of exciplex, absorption spectra of hydrogen bonding interaction, absorption and emission spectra after proton transfer and different lifetimes before and after protonation. The interaction mechanism of DMN and sulfuric acid through first the CT complex and exciplex then hydrogen bonding and finally proton transfer is proposed.     

基于(R)-1,1’-联萘硫脲的手性荧光受体: 合成与手性识别

Two chiral fluorescent receptors 1 and 2 based on (R)-1,1‘-binaphthylene-2,2‘-bisthiourea were synthesized, and their chiral recognition properties for enantiomeric mandelate anions were studied by fluorescence spectra and molecular modeling. Addition of the L- and D-mandelate anions caused considerable fluorescent increases in the fluorescent intensity of the host solution. The L-enantiomer can enhance the fluorescence intensity of 1 much more than the D-enantiomer can do, and 1 shows a better enantioselective recognition ability than 2.     

Molecular modeling and spectroscopic studies on the binding of guaiacol to human immunoglobulin

The fluorogenic property of guaiacol was exploited for the first time to analyze the interaction with target protein as a probe by molecular modeling, fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy. Molecular docking was performed to reveal the possible binding mode or mechanism and suggested that guaiacol can strongly bind to human immu- noglobulin (HIgG). It is considered that guaiacol binds to HIgG mainly by a hydrophobic interaction and there are two hydrogen bond interactions between the drug and the residues LEU 80 and ASP 65, which is in good agreement with the results from the experimental thermodynamic parameters (the enthalpy change △H0 and the entropy change △S0 were calculated to be 65.55 kJ·mol-1 and 132.95 J·mol-1·K-1 according to the Vant’ Hoff equation). Data obtained by the fluorescence spectroscopy indicated that binding of guaiacol with HIgG leads to dramatic enhancement in the fluorescence emission intensity along with significant occurrence of efficient Frster resonance energy transfer (FRET) from the residue of HIgG to the protein bound guaiacol. From the low value of fluorescence anisotropy (r = 0.06), it is argued that the probe molecule is located in the motionally unrestricted environment of the protein. The alterations of protein’s secondary structure in the presence of guaiacol in aqueous solution were quantitatively calculated by the evidences from FT-IR and CD spectroscopes.     

Spectroscopic characterization of intramolecular charge transfer of sodium 4-(N,N-dimethylamino)naphthalene-1-sulfonate

In this paper, a new dual fluorescent N,N-dimethylaminonaphthalene derivative, sodium 4-(N,N-dimethylamino)naphthalene-1-sulfonate (SDMDNS), was reported. It was found that SDMDNS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as methanol, dioxane and acetonitrile. Only a single broad band emission at ca. 420 nm was observed in the short wavelength region in organic solvents. The dual fluorescence of SDMDNS in water was found at 423 and 520 nm, respectively. Introduction of organic solvent as ethanol into aqueous solution of SDMDNS leads to blue shift of the long-wavelength emission, and this was evidently supported by introduction of cyclodextrin or surfactant in the aqueous solution. It indicates that a highly polar solvent was required to bring out dual fluorescence; furthermore, the short wavelength fluorescence is emitted from locally excited (LE) state and the long wavelength fluorescence is emitted from charge transfer (CT) state. The pH dependence of the dual fluorescence of SDMDNS demonstrates that the neutral form of the molecular has a higher ratio of CT band intensity to LE band. Temperature effect on the excited state of SDMDNS was also examined and gave stabilization enthalpy (-DeltaH ) of the CT reaction 8.7 kJ mol(-1).     

A novel fluorophore with dual fluorescence: local excited state and photoinduced electron-transfer-promoted charge-transfer state.

Absorption and emission spectra of 9-N,N-dimethylaniline decahydroacridinedione (DMAADD) have been studied in different solvents. The fluorescence spectra of DMAADD are found to exhibit dual emission in aprotic solvents and single emission in protic solvents. The effect of solvent polarity and viscosity on the absorption and emission spectra has also been studied. The fluorescence excitation spectra of DMAADD monitored at both the emission bands are different. The presence of two different conformation of the same molecule in the ground state has lead to two close lying excited states, local excited (LE) and charge transfer (CT), and thereby results in the dual fluorescence of the dye. A CTstate involving the N,N-dimethylaniline group and the decahy droacridinedione chromophore as donor and acceptor, respectively, has been identified as the source of the long wavelength anomalous fluorescence. The experimental studies were supported by ab initio time dependent-density functional theory (TDDFT) calculations performed at the B3LYP/6-31G* level. The molecule possesses photoinduced electron transfer (PET) quenching in the LE state, which is confirmed by the fluorescence lifetime and fluorescent intensity enhancement in the presence of transition metal ions.     

Tunable Dual Fluorescence of 3‐(2,2′‐Bipyridyl)‐Substituted Iminocoumarin

3‐(2,2′‐Bipyridyl)‐substituted iminocoumarin molecules (compounds 1 and 2 ) exhibit dual fluorescence. Each molecule has one electron donor and two electron acceptors that are in conjugation, which leads to fluorescence from two independent charge transfer (CT) states. To account for the dual fluorescence, we subscribe to a kinetic model in which both CT states form after rapid decays from the directly accessed S₁ and S₂ excited states. Due to the slow internal conversion from S₂ to S₁, or more likely the slow interconversion between the two subsequently formed CT states, dual emission is allowed to occur. This hypothesis is supported by the following evidence: 1) the emission at short and long ends of the spectrum originates from two different excitation spectra, which eliminates the possibility that dual emission occurs after an adiabatic reaction at the S₁ level. 2) The fluorescence quantum yield of compound 2 grows with increasing excitation wavelength, which indicates that the high‐energy excitation elevates the molecule to a weakly emissive state that does not internally convert to the low‐energy, highly emissive state. The intensity of the two emission bands of 1 is tunable through the specific interactions between either of the two electron acceptors with another species, such as Zn²⁺ in the current demonstration. Therefore, the development of ratiometric fluorescent indicators based on the dual‐emitting iminocoumarin system is conceivable. Further fundamental studies on this series of compounds using time‐resolved spectroscopic techniques, and explorations of their applications will be carried out in the near future.     

分子内电荷转移双重荧光体识别阴离子研究

设计合成阴离子受体是近年来超分子化学中一个颇为活跃的研究领域[1～ 7] .其中荧光法以其高灵敏度和高选择性等特点使发光受体的设计合成备受关注 [6 ,7] .分子内电荷转移 (Intramolecular charge transfer,ICT)原理已被成功地用于构筑阳离子荧光传感体系[8] ,但将其应用于阴离子识别的研究尚鲜见报道[9～ 12 ] .本文设计合成了 ICT荧光体对二甲氨Scheme 1　 The structures of anion receptors基苯甲酰肼 (DMABH,结构见 Scheme 1 ) ,研究了 DMABH与阴离子如 HSO- 4,Ac O- ,H2 PO- 4,Cl O- 4,NO- 3,Cl- 和 Br- 等结合后的光…     

Pressure‐Induced Emission Enhancement of a Series of Dicyanovinyl‐Substituted Aromatics: Pressure Tuning of the Molecular Population with Different Conformations

A series of dicyanovinyl‐substituted aromatic compounds (Ar‐DCV; Ar=9‐anthracenyl, 1‐naphthyl, 1‐pyrenyl) with dual fluorescence are prepared, and their emission properties—when molecularly dispersed in a polymer medium—are investigated under pressure perturbation. The total emission intensity is enhanced drastically from ambient pressure up to 70 kbar. Emission 30–107 times more intense than that at ambient pressure is observed at higher pressure. In dual emission, the enhancement of the local excited state (LE state) is significantly different from that of the intramolecular charge‐transfer state (ICT state). The intensity of the ICT emission increases faster (30–370 times) than that of the LE emission (less than 20 times). In accordance with spectroscopic data, emission dynamics at different pressures, and computational studies on the molecular conformations of these compounds, a kinetic model is proposed to explain the effect of pressure on the emissive properties of the Ar‐DCV compounds from the point of view of pressure‐dependent populations of the species in the ground state.     

Unusual Solvatofluorochromism of the Asymmetrically Substituted Aromatic Acetylene Derivative CNAacDMA**

The photophysical properties of the newly synthesized unsymmetrically substituted aromatic acetylene derivative 9-(2-(4-(N,N-dimethylamino)phenyl)ethynyl)anthracene-10-carbonitrile (CNAacDMA) were investigated with the steady-state and time-resolved fluorometry. In saturated hydrocarbon solvents, only fluorescence from a locally-excited state (LE) is recorded. In more polar solvents however, excitation of this dye leads to a charge transfer state (CT). In moderate polar solvents (ϵ=4–8) dual emission is observed as a result of competition between structural change and intramolecular charge transfer in the excited state. In polar solvents only one emission band, at shorter wavelength than CT emission, is observed, indicating a bidirectional solvatofluorochromism.     

Donor–σ–Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion

A family of organic emitters with a donor–σ–acceptor (D‐σ‐A) motif is presented. Owing to the weakly coupled D‐σ‐A intramolecular charge‐transfer state, a transition from the localized excited triplet state (³LE) and charge‐transfer triplet state (³CT) to the charge‐transfer singlet state (¹CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200–400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D‐σ‐A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.     

Ratiometric dual fluorescent receptors for anions under intramolecular charge transfer mechanism

A series of the intramolecular charge transfer (ICT) dual fluorescent receptors with anion binding site in the electron acceptor were designed and synthesized. These receptors exhibited dual fluorescence in acetonitrile and the charge transfer (CT) emission energy was found to correlate linearly with the Hammett constant of the substituent existing in the electron acceptor, which is the basis for anion sensing. Dual fluorescence of these receptors was found to be sensitive to the presence of anions such as fluoride and acetate and the receptors can be employed as ratiometric fluorescent sensors for anions.     

Luminescence Properties of C‐Diazaborolyl‐ortho‐Carboranes as Donor–Acceptor Systems

Seven derivatives of 1,2‐dicarbadodecaborane (ortho‐carborane, 1,2‐C₂B₁₀H₁₂) with a 1,3‐diethyl‐ or 1,3‐diphenyl‐1,3,2‐benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low‐energy fluorescence emissions with large Stokes shifts of 15100–20260 cm^?1 and quantum yields (Φ_F) of up to 65 % in the solid state. The low‐energy fluorescence emission, which was assigned to a charge‐transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C? C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660–18090 cm^?1 for the CT bands and 1960–5540 cm^?1 for the high‐energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ_F values between 8–32 %. Two distinct excited singlet‐state (S₁) geometries, denoted S₁(LE) and S₁(CT), were observed computationally for the benzodiazaborolyl‐ortho‐carboranes, the population of which depended on their orientation (ψ). TD‐DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C‐diazaborolyl‐ortho‐carboranes were viewed as donor–acceptor systems with the diazaborolyl group as the donor and the ortho‐carboranyl group as the acceptor.