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White organic light-emitting diodes (WOLEDs) using thermally activated delayed fluorescence (TADF)-based single emissive layer (SEL) have attracted enormous attention because of their simple device structure and full exciton utilization potential for high efficiency. However, WOLEDs made of an all-TADF SEL usually exhibit serious efficiency roll-off and poor color stability due to serious exciton-annihilation and unbalanced radiative decays of different TADF emitters. Herein, a new strategy is proposed to manipulate the TADF-sensitized fluorescence process by combining dual-host systems of high triplet energy with a conventional fluorescent emitter of complementary color. The multiple energy-funneling paths are modulated and short-range Dexter energy transfer is largely suppressed due to the steric effect of peripheral tert-butyl group in the blue TADF sensitizer. The resulting all-fluorescent WOLEDs achieve an unprecedentedly high external quantum efficiency of 21.8% with balanced white emission of Commission Internationale de l'Eclairage coordinate of (0.292, 0.343), accompanied with good color stability, reduced efficiency roll-off, and prolonged operational lifetime. These findings demonstrate the validity of this strategy for precisely allocating the exciton harvesting in SEL WOLEDs.

High-efficiency orange and red thermally activated delayed fluorescent (TADF) organic light-emitting diodes were fabricated based on a pair of isomers 3,6,11-triAC-BPQ and 3,6,12-triAC-BPQ, containing a rigid dibenzo[f,h]pyrido[2,3-b]quinoxaline (BPQ) core and three 9,9-dimethyl-9,10-dihydroacridine (Ac) donors. Both materials exhibited red emission in neat films and small singlet–triplet energy gaps. Compared with the stable intramolecular charge transfer (ICT) state of 3,6,12-triAC-BPQ, 3,6,11-triAC-BPQ showed hybridized local and charge transfer (HLCT) character due to the H-bond between the 11-position Ac and 10-position N atom. As a result, the doped film of 3,6,11-triAC-BPQ showed a high photoluminescence quantum yield (PLQY) and the related device showed a high external quantum efficiency (EQE) of 22.0% in the orange–red region.

Exploiting effective orange-red thermally activated delayed fluorescent (TADF) emitters is still challenging. In this work, we proposed a method by using a crooked donor (D) moiety instead of its conventional planar form to balance the opposite influences of frontier molecular orbital overlap on the reverse intersystem crossing and the singlet radiative decay rate. A novel orange-red TADF emitter, named 2-(4-(9,9-dimethyl-4-phenylacridin-10(9H)-yl)phenyl)anthracene-9,10-dione (AQ-PhDMAC), was accordingly designed and synthesized. Owing to the steric effect of the α-phenyl ring in 9,9-dimethyl-4-phenyl-9,10-dihydroacridine (α-PhDMAC), a relatively small singlet–triplet energy splitting of 0.22 eV and a high fluorescence quantum yield of 0.89 can be realized simultaneously. The orange-red organic light-emitting diode based on AQ-PhDMAC exhibited a maximum external quantum efficiency of 18.1%, much improved compared with the 13.7% efficiency of the α-phenyl ring-free control emitter (AQ-DMAC). These results propose a new viewpoint that enforcing crooked D segments by large steric hindrance actually has a great potential for applications in orange-red TADF molecular design, to improve their electroluminescence efficiency.

Two fluorescent probes (L1 and L2) based on an imidazole unit were synthesized for the specific detection of ClO− and HSO3−. Density functional theory (DFT) calculations were used to assist in designing the probes. As predicted, L1 could be used to detect ClO− in real water samples and in living cells. It was shown to be a quenching probe. L2 could be used to monitor HSO3− in living cells and is an enhanced fluorescence probe. Further details of the fluorescence recognition mechanism were obtained via HRMS analysis. Moreover, both fluorescent probes showed relatively low detection limits (0.96 and 0.59 μM, respectively), and fast and highly selective fluorescence responses.

The design and synthesis of highly efficient thermally activated delayed fluorescence (TADF) emitters with an electroluminescence wavelength beyond 600 nm remains a great challenge for organic light-emitting diodes (OLEDs). To solve this issue, three TADF molecules, xDMAC–BP (x = 1, 2, 3), are developed in combination with the rigid planar dibenzo[a,c]phenazine (BP) acceptor core and different numbers of 9,9-dimethylacridan (DMAC) donors. All these emitters possess stable internal charge transfer and a large dihedral angle between the donors and planar BP core. The emission wavelength can be regulated from 541 to 605 nm by increasing the number of the donor DMAC units because of the controllable tuning of the intramolecular charge transfer effect and the molecular geometrical structure. The photoluminescence quantum yields of these emitters are improved from 42 to 89% with the increase in the number of DMAC units. The orange-red OLEDs employing the xDMAC–BP emitters exhibit maximum external quantum effici...

By introducing two novel electron-donating (D) moieties dibenzothiophene (DBT) and dibenzofuran (DBF) as the secondary D groups, we designed and synthesized four novel blue thermally activated delayed fluorescence (TADF) emitters DBTCz-Trz, DBFCz-Trz, BDBTCz-Trz and BDBFCz-Trz. The secondary DBF and DBT segments all significantly participated in the highest occupied molecular orbital (HOMO) delocalization, resulting in effective TADF characteristics and high photoluminescence quantum yields simultaneously for all four emitters. In the devices, DBTCz-Trz and DBFCz-Trz successfully exhibit identical blue emission with a peak at 472 nm and a CIE coordinate of (0.17, 0.28) in the devices, while BDBTCz-Trz and BDBFCz-Trz exhibit cyan emissions. Moreover, the maximum forward-viewing external quantum efficiencies are determined to be as high as 21.7% for DBTCz-Trz, 21.6% for DBFCz-Trz, 23.4% for BDBTCz-Trz, and 25.1% for BDBFCz-Trz, respectively. These results not only prove the great potential of amine-free electron-donating components such as DBF and DBT in constructing TADF emitters for electroluminescence, but they also reveal the importance of extending the frontier orbital molecular distributions for TADF molecular optimization.

Thermally activated delayed fluorescence (TADF) emitters normally suffer from serious concentration sensitivity, realizing peak electroluminescence efficiencies with precise control of the doping concentrations, which may hinder their practical applications in organic light emitting devices (OLEDs). In this work, we developed TADF emitter 2′,7′-di(10H-phenoxazin-10-yl)spiro[fluorene-9,9′-thioxanthene]10′,10′-dioxide (SPFS-PXZ) based on conventional TADF emitter 10,10′-(sulfonylbis(4,1-phenylene))bis(10H-phenoxazine) (DPS-PXZ). By introducing a fluorene group, the molecular rigidity and steric hindrance of SPFS-PXZ are improved greatly, which contributes to suppressing the strong π–π stacking tendency between phenoxazine segments and reduces intermolecular interactions. In turn, SPFS-PXZ successfully exhibits low concentration sensitivity in OLEDs, and keeps high maximum external quantum efficiencies (EQEs) over 20.8% with a small EQE fluctuation of 2.1% in a wide doping concentration range from 10 wt% to 50 wt%. These results prove that SPFS-PXZ is an ideal model to develop efficient TADF emitters with low concentration sensitivity.

By rationally introducing glutathione functionalized 1, 8–naphthalimide, a novel fluorescent chemosensor (NG) was successfully synthesized. NG can high selectively and sensitively recognize Fe3+/Hg2+ ions through quenching of fluorescence among all kinds of common metal ions in aqueous medium. The binding stoichiometry ratio of NG–Fe3+ is verified as 2:1and NG–Hg2+ as 1:2 confirmed by Job's plot method, FT-IR, 1H NMR and ESI–MS spectrum, and the possible sensing mechanism were also proposed. The chemosensor NG toward Fe3+ and Hg2+ displays the excellent advantages of high selectivity and sensitivity, low detection limits (7.92 × 10−8 and 4.22 × 10−8 M), high association constants (3.37 × 108 and 8.14 × 104 M−2), instataneous response (about 10s) and wide pH response range (3.0–8.0). Importantly, the chemosensor NG was successfully applied to determine Hg2+ in tap water. Meanwhile, the test strips based on NG were prepared, which could conveniently and efficiently detect Fe3+ and Hg2+. Moreover, the complex of NG and Fe3+ (NG–Fe3+) showed high selectivity and sensitivity for H2PO4‾ over many other anions in the same medium.

The development of efficient long-wavelength TADF emitters has been full of challenges owing to the various strict molecular design limiting factors. Herein, two orange-red TADF emitters, namely 3DMAC-BP-Br and 3DMAC-BP-CN, based on donor 9,9-dimethyl-9,10-dihydroacridine (DMAC) and rigid acceptor dibenzo[a,c]phenazine (BP) modified by electron-withdrawing bromine atom or cyano group, were designed and synthesized. Both emitters have large twisted D-A-D structure. The strong electron-withdrawing capabilities of the bromine atom or cyano group can dramatically affect photoelectric properties of the emitters by enhancing the intramolecular charge transfer (ICT) effect and enlarge conjugation with the BP group. Hence, both emitters have high PLQY values (83% and 92%, respectively) in doped films and possess simultaneously small ΔEST values (0.04 and 0.02 eV, respectively). As a result, both 3DMAC-BP-Br and 3DMAC-BP-CN show superior device performance. Especially, DMAC-BP-CN based OLED exhibits a maximum external quantum efficiency (EQE) of 22.43% and low turn-on voltage of 2.8 V.

White organic light-emitting diodes (WOLEDs) with thermally activated delayed fluorescence-sensitized fluorescence (TSF) have aroused wide attention, considering their potential for attaining ultimate high efficiency and long lifetime with pure organic fluorescent emitters. To develop high-performance TSF-based WOLEDs, an efficient energy transfer system is built by combining a conventional host, a stable blue delayed fluorescence sensitizer, and an orange fluorescent dopant in a single-emissive-layer. Transient photoluminescence measurements decipher the Forster resonance energy transfer process with the high exciton utilization and the suppressed Dexter energy transfer in the single-emissive-layer. The TSF-based WOLEDs achieve a maximum external quantum efficiency of 20.9% and the balanced white emission with color coordinates of (0.31, 0.41) because of the partial energy transfer from blue sensitizer to the fluorescent dopant. Moreover, the TSF-WOLEDs exhibit a half-lifetime of ~2,800 h at an initial brightness of 1,000 cd m −2, which can be further improved to >12,000 h by implementing the stacked structure and light outcoupling enhancement techniques. The prolonged device stability is because the TSF system can effectively prevent exciton leakage and suppress the accumulation-caused exciton-annihilation.

Three D-σ-A type thermally activated delayed fluorescent materials (TADF), AQ-S-Cz, AQ-S-DPA and AQ-S-DMAC, with sulfur atom connect donors and acceptor, were designed and synthesized. All of the emitters exhibit small ΔEST (

3-(Phenylsulfonyl)pyridine (PSP), an unreported acceptor, is used to construct two thermally activated delayed fluorescent materials (TADF), PSPP and PSPBP, with rigid PXZ as donor in 3-position or 3, 5-position of PSP. Both PSPP and PSPBP have large twisted structure due to highly steric hindrance, resulting in small ΔEST. Simultaneously, the frontier molecular orbitals of PSPP and PSPBP show limited spatial overlap, which improve photoluminescence quantum yields. Both emitters have distinct TADF performance. The OLEDs based on these emitters exhibit good photoelectric properties. This work enriches the acceptor selection scope and possesses crucial significance to developing new TADF molecules.

Two highly efficient thermally activated delayed fluorescent (TADF) materials with twisted donor-acceptor-donor (D-A-D) structure, DMACBB and PXZBB, have been designed and synthesized based on bis(phenylsulfonyl)benzene as the acceptor (A) and 9,9-dimethyl-9,10-dihydroacridine (DMAC) or phenoxazine (PXZ) as the donor (D). Attaching the donor to the 3, 3′-positions of bis(phenylsulfonyl)benzene obtains larger torsion angle between donor and acceptor as well as suitable ICT effects, which results in almost complete separation of their FMOs and limited overlap. Both emitters successfully achieve small ΔEST (≤0.2 eV), simultaneously exhibit high photoluminescence quantum yields (≥80%). Both of them possess distinct TADF features. The DMACBB-based device exhibits sky blue emission with the peak at 472 nm, while the PXZBB-based device shows slightly red-shifted and emits green light with the peak at 507 nm because of the stronger electron-donating ability of PXZ than that of DMAC. The TADF-OLED based on DMACBB achieves higher the maximum external quantum efficiency (EQEmax of 10.1%) than the TADF-OLED based on PXZBB (EQEmax of 8.2%) with the turn-on voltage of 3.5 V.

A novel pyrazoline with benzimidazole substituent was conveniently synthesized, starting from a chalcone and 2-hydrazinylpyridine. The addition of Ni 2+ to ethanol solution of the synthesized pyrazoline resulted in a rapid color change from blue to green which allows the selective detection of Ni 2+ ion over a great number of other metal ions. The association constant for the 1:1 complex was determined to be 2.72 × 10 7 M −1 .

Two novel thermally activated delayed fluorescence (TADF) emitters, 3-phenylquinolino[3,2,1- de]acridine-5,9-dione (3-PhQAD) and 7-phenylquinolino[3,2,1- de]acridine-5,9-dione (7-PhQAD), were designed and synthesized based on a rigid quinolino[3,2,1- de]acridine-5,9-dione (QAD) framework. With the effective superimposed resonance effect from electron-deficient carbonyls and electron-rich nitrogen atom, both emitters realize significant TADF characteristics with small Δ ESTs of 0.18 and 0.19 eV, respectively. And, molecular relaxations were dramatically suppressed for both emitters because of their conjugated structure. In the devices, 3-PhQAD realizes superior performance with a maximum external quantum efficiency (EQE) of 19.1% and a narrow full width at half-maximum (FWHM) of 44 nm, whereas a maximum EQE of 18.7% and an extremely narrow FWHM of 34 nm are realized for 7-PhQAD. These superior results reveal that apart from nitrogen and boron-aromatic systems, QAD framework can also act as a TADF matrix with effective resonance effect, and QAD derivatives are ideal candidates to develop TADF emitters with narrow FWHMs for practical applications.

Element doping is recognized as a powerful way to modify surface defect structure and further enhance the fluorescence performance of graphene quantum dots (GQDs). N-doped, S-doped and S, N co-doped GQDs were synthesized to explore the influence of element doping on fluorescence sensing of dopamine (DA) biomolecules. Two interesting works are found, one is that the N-doped GQDs with urea as N source are more effective than the S-doped and S,N co-doped GQDs, characterized by the higher quantum yield (QY) up to 78% and sensitive fluorescence quenching performance to DA. The other is that the N-doped GQDs with ethylenediamine as N source have the highest QY up to 95%, however, exhibits no quenching performance to DA. This abnormal observation is discussed based on the microstructure analysis. Under the optimal reaction condition, the N-doped GQDs exhibit a dual linear relationship of quenching intensity with DA concentration in the range of 10–3000 nM and 3000–7000 nM with detection limits of 3.3 and 611 nM, respectively. The quenching mechanism of N-doped GQDs toward DA is explored from the view of N chemical states, biomolecule structure of DA homologues and redox reaction of DA.

In the present study, the experimental and theoretical methods were used to analyze the binding interaction of food dye, curcumin with trypsin. The results of fluorescence spectroscopic measurements indicated that curcumin binding resulted in the obviously intrinsic fluorescence quenching with the increase concentration of curcumin. This binding interaction is a spontaneous process with the estimated enthalpy and entropy changes being −15.70 kJ mol−1 and 40.25 J mol−1 K−1, respectively. Hydrogen bonds and hydrophobic forces played an important role in the complex formation between curcumin and trypsin. Moreover, curcumin could enter into the primary substrate-binding pocket and makes the activity of trypsin decrease remarkably with the increasing concentration of curcumin.

Thermally activated delayed fluorescence (TADF) chiral emitters attract widespread attention due to their high exciton utilization as well as potential applications. In this work, we developed a pair of chiral donors, (R) and (S)-9-methyl-2,9-diphenyl-9,10-dihydroacridine (PMAc), for general TADF molecular design. The enantiomers (R) and (S)-TTR-PMAc are accordingly constructed. Interestingly, they are not only TADF emitters, but also possess dual stable conformations, i.e. nearly planar and nearly orthogonal conformations. (R) and (S)-TTR-PMAc show similar physical properties under conventional non-polarized environment. While under chiroptical environments, they exhibit obvious mirror-like circular dichroism (CD) and circularly polarized luminescence (CPL) properties. Moreover, by further comparing the CPL properties originated from each conformer, we confirm that molecular conformations can significantly influence the chiroptical performance.

The aim of this study is to construct N-containing heterocyclic probes with large conjugate structures. Two triazolopyrimidine analogs LK-1 and LK-2 were designed and synthesized. Between them, LK-2 has a higher fluorescence quantum yield and selected as a fluorescent probe for detecting 2,4,6-trinitrophenol (TNP). Whether DMF or H2O as solvent, probe LK-2 shown low detection limit apparently (0.025 and 0.44 μM), fast and highly selective fluorescence response to TNP compared to other nitro-aromatic compounds. The static quenching mechanism is demonstrated by fluorescence lifetime. Nuclear magnetic titration and theoretical calculations further explain the identification process. What's more, application of LK-2 in actual water samples and test strip experiments demonstrate the potential of probe in practical significance.

The influences of caffeine, lysozyme and the joint application of them on the hepatoma cell line HepG2 proliferation inhibition and cell apoptosis were observed by 3-(4, 5-dimethyl-2-thiazyl)-2, 5-diphenyl-2H-tetrazolium bromide assay and Hoechst 33342, which showed the proliferation inhibition rate of the joint application on HepG2 cells was 47.21%, significantly higher than caffeine or lysozyme, and the joint application promoted the apoptosis of HepG2 cells obviously. Van't Hoff classical thermodynamics formula, the Foster theory of non-radiation energy transfer and fluorescence phase diagram were used to manifest that the process of lysozyme binding to caffeine followed a two-state model, which was spontaneous at low temperature driven by enthalpy change, and the predominant intermolecular force was hydrogen bonding or Van der Waals force to stabilize caffeine-lysozyme complex with the distance 5.86nm. The attenuated total reflection-Fourier transform infrared spectra indicated that caffeine decreased the relative contents of α-helix and β-turn, which inferred the structure of lysozyme tended to be "loose". Synchronous fluorescence spectra and ultraviolet spectra supported the above conclusion. The amino acid residues in the cleft of lysozyme were exposed and electropositivity was increased attributing to the loose structure, which were conducive to increasing caffeine concentration on the HepG2 cell surface by electrostatic interaction to show synergistic effect.

Four novel high-dimensional metal–organic rotaxane frameworks (MORFs) were successfully fabricated by cucurbit[6]uril-based pseudorotaxanes ([PR43]) and rigid carboxylate ligands by adjusting the synthesis temperature and the length of ligands. Compound 1 represents a three periodic 2-fold interpenetrating dia network based on a binuclear {Cd2Cl4O4} second building unit (SBU). 2 and 3 are isostructural pcu networks constructed by binuclear and trinuclear cadmium clusters, respectively, while compound 4 is a two-dimensional layered network with a large grid 44.3 × 19.8 A2. Furthermore, their fluorescent properties in different solvents are investigated.

An environment-friendly fluorescent nano-hybrid hydrogel has been synthesized successfully, from cellulose nanocrystal (CNC), acrylic acid (AA) and phosphorescent Eu2+/Dy3+ doped SrAl2O4 via free radical polymerization. The hydrogel network matrix fixed Eu2+/Dy3+ doped SrAl2O4 nanoparticles by polymer chains with coordinate bonds that prevented particles from aggregating and quenching in water. The fluorescent nano-hybrid hydrogel exhibited extremely high water absorption of which the swelling ratio in distilled water and NaCl salt solution were respectively of 323.35 g/g and 32.65 g/g. Furthermore, the hydrogel displayed excellent water retention property that can keep half of the moisture even exposed to 80 °C for 210 min. Besides, the hydrogel had bright green fluorescence under the sunlight or ultraviolet excitation, and the fluorescence intensity was up to 125477 after swelling 50 times in water. The time-resolved photoluminescence (TRPL) afterglow decay examination showed that the fluorescent emission persisted for 4 h after hydrogels excited at 368 nm wavelength UV-light for 10 min. The fluorescence intensity behaved significant linear relationship with the swelling ratio. As a result, these hydrogels were considered as promising candidates for the preparation of stable and sensitive sensor materials in green water detection.

The interaction between a hydrophobic-functionalized PAMAM dendrimer (PAMAM-NH2-C12, 25%, G4) and bovine serum albumin (BSA) has been investigated by circular dichroism (CD), UV-vis, and fluorescence spectroscopic methods and molecular modeling. The analysis of the effects of dendrimer complexation on the stability and conformation of BSA indicated that the binding process of the hydrophobic-functionalized dendrimer with BSA induced the relatively large changes in secondary structure of protein. Thermal denaturation of BSA, when carried out in the presence of dendrimer, also indicated that this hydrophobic-functionalized dendrimer acted as a structure destabilizer for BSA. The hydrophobic, electrostatic, and hydrogen bonding forces played important roles in the complex formation. The putative binding site of PAMAM-NH2-C12 (25%) dendrimer on BSA was near to domain I and domain II. The effect of hydrophobic modification on the stability and structure of BSA would find useful information on the cytotoxicity of PAMAM dendrimer.

To explore the effect and mechanism of Qingfei Mixture (), a Chinese medicine, in treating mycoplasma pneumonia (MP) in MP patients and rat model METHODS: A total of 46 MP children with phlegm heat obstructing Fei (Lung) syndrome were randomly assigned to two groups by the method of random number table, with 23 children in each group. The control group was treated with intravenous infusion of azithromycin; the treatment group received intravenous infusion of azithromycin and oral administration of Qingfei Mixture. The treatment course was 7 days. Major symptoms and minor symptoms were observed and scored before and after treatments. A rat model of MP was also established. A total of 120 wistar rats were randomly divided into 5 groups: a normal group, infection group, Qingfei Mixture treatment group, azithromycin treatment group, and Qingfei Mixture + azithromycin treatment group. Each group contained 24 rats, from which every 6 were euthanatized 1, 3, 7 and 14 days after infection. MP DNA in pulmonary tissue homogenates was detected using real-time fluorescence quantitative polymerase chain reaction. Pathology was assessed after hematoxylin (HE) staining and lung tissue pathology scores were determined in pulmonary tissue. Transmission electron microscopic detection and electronic image analysis were performed on lung tissue 3 days after infection. Interleukin (IL)-17 was detected in serum using enzymelinked immunosorbent assay (ELISA) 7 days after infection.In the clinical study, both control and the treatment group showed improved results on removing symptoms of phlegm heat syndrome compared to the control group (P0.05). In animal experiments, On the 7th day after MP infection, as detected by electron microscopy, the pulmonary capillary basement membranes of the azithromycin + Qingfei Mixture treatment group were much thinner than those of the azithromycin or Qingfei mixture treatment groups (P0.05). The level of serum IL-17 in the azithromycin + Qingfei Mixture treatment group was lower than that in the azithromycin or Qingfei Mixture groups (P0.01).Both Qingfei Mixture and azithromycin have therapeutic effects on mycoplasma pneumoniae pneumonia, but the combination of both agents had the greatest effect.

The interactions of Cu 2+ with urease were investigated by fluorescence, UV/vis, CD, synchronous fluorescence, and three-dimensional fluorescence spectra techniques. Cu 2+ effectively quenched the intrinsic fluorescence of urease via static quenching. The binding constant K A , the binding site n and the thermodynamic parameters are obtained. The process of binding Cu 2+ to urease was a spontaneous molecular interaction procedure with electrostatic interaction. The conformation of urease was discussed by UV/vis, CD, synchronous and three-dimensional fluorescence techniques.

In this report, the binding interaction of BPA with pepsin has been explored by spectroscopic and molecular modeling methods. Quenching of fluorescence of pepsin with increasing BPA concentration is a useful tool in the analysis of thermodynamic parameters. The results showed that the hydrophobic, steric contacts and hydrogen bonds interactions played major roles in stabilizing the complex. The binding of BPA to pepsin induced some micro-environmental and conformational changes in pepsin. The docking studies results showed that BPA entered into the hydrophobic cavity of pepsin. The interaction of pepsin with BPA occurs in the area between domain I and domain III.

The interactions between pentachlorophenol (PCP) and jack bean urease were studied using UV/vis absorption, CD, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectroscopic techniques. The fluorescence data showed that the fluorescence quenching of urease by PCP the results of the formation of a PCP–urease complex involving a hydrophobic interaction. The distance r between the donor (urease) and acceptor (PCP) was obtained from the fluorescence resonance energy transfer. The effect of PCP on the conformation of urease was analyzed using UV/vis absorption, synchronous fluorescence and three-dimensional fluorescence spectroscopic techniques. The result showed that PCP can enter into the hydrophobic pocket at the interface of urease and that the micro environments around the tyrosine and tryptophan residues were changed.

The interaction between lysozyme and cinnamic acid was investigated systematically by ultraviolet–vis absorbance, circular dichroism, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques at pH 7.40. The binding constants, quenching mechanism, and the number of binding sites were determined by the quenching of lysozyme fluorescence in presence of cinnamic acid. The results showed that the fluorescence quenching of lysozyme by cinnamic acid was a result of the formation of cinnamic acid–lysozyme complex. The hydrophobic and electrostatic interactions played major roles in stabilizing the complex; the distance r between donor and acceptor was obtained to be 2.07 nm according to Forster’s theory; the effect of cinnamic acid on the conformation of lysozyme was analyzed using synchronous fluorescence, circular dichroism and three-dimensional fluorescence spectra.

The interaction between K(2)Cr(2)O(7) and urease was investigated using fluorescence, UV-vis absorption, and circular dichroism (CD) spectroscopy. The experimental results showed that the fluorescence quenching of urease by K(2)Cr(2)O(7) was a result of the formation of K(2)Cr(2)O(7)-urease complex. The apparent binding constant K (A) between K(2)Cr(2)O(7) and urease at 295, 302, and 309 K were obtained to be 2.14 × 10(4), 1.96 × 10(4), and 1.92 × 10(4) L mol(-1), respectively. The thermodynamic parameters, ΔH° and ΔS° were estimated to be -5.90 kJ mol(-1), 43.67 J mol(-1) K(-1) according to the Van't Hoff equation. The electrostatic interaction played a major role in stabilizing the complex. The distance r between donor (urease) and acceptor (K(2)Cr(2)O(7)) was 5.08 nm. The effect of K(2)Cr(2)O(7) on the conformation of urease was analyzed using UV-vis absorption, CD, synchronous fluorescence spectroscopy, and three-dimensional fluorescence spectra, the environment around Trp and Tyr residues were altered.

The interaction of benzidine (BEN) with trypsin was studied by fluorescence spectrum. It was shown that BEN has quenched the fluorescence launching from trypsin by reacting with it and forming a certain kind of new complex. The quenching and energy transfer mechanisms were discussed. The binding constants and thermodynamic parameters at three different temperatures, the binding locality, and the binding power were obtained. The conformation of trypsin was discussed by synchronous and three-dimensional fluorescence techniques.

The interactions between rutin and trypsin were investigated by UV-Vis absorption, CD, fluorescence, resonance light-scattering spectra, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. Rutin effectively quenched the intrinsic fluorescence of trypsin via static quenching. The enthalpy change and entropy change were estimated to be −8.23 kJ·mol−1 and 53.66 J·mol−1·K−1 according to the van't Hoff equation. The process of binding rutin to trypsin was a spontaneous molecular interaction procedure. This result indicates that hydrophobic and electrostatic interactions played a major role in stabilizing the complex. The conformation of trypsin was discussed by CD, synchronous, and three-dimensional fluorescence techniques.

The interactions of 2, 4-dinitrophenol and 2, 4-dichlorphenol with trypsin were investigated by fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. The 2, 4-dinitrophenol and 2, 4-dichlorphenol effectively quenched the intrinsic fluorescence of trypsin via static quenching. The process of binding 2, 4-dinitrophenol and 2, 4-dichlorphenol with trypsin was a spontaneous molecular interaction procedure. The electrostatic repulsion does favor the interaction between 2, 4-DNP and trypsin. However, the interaction of 2, 4-DCP and trypsin can be explained on the basis of hydrogen bonding and van der Waals. The results of synchronous fluorescence spectroscopy and three-dimensional fluorescence spectra indicated that the structure of these trytophan and tyrosine residues environments were altered by 2, 4-DNP and 2, 4-DCP.

The interaction between three purine alkaloids (caffeine, theophylline, and theobromine) and human serum albumin (HSA) was investigated using UV/vis absorption, circular dichroism (CD), fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques. The results revealed that three alkaloids caused the fluorescence quenching of HSA by the formation of alkaloid–HSA complex. The binding site number n and apparent binding constant K A , corresponding thermodynamic parameters the free energy change (Δ G ), enthalpy change (Δ H ), and entropy change (Δ S ) at different temperatures were calculated. The hydrophobic interaction plays a major role in stabilizing the complex. The distance r between donor (HSA) and acceptor (alkaloids) was obtained according to fluorescence resonance energy transfer. The effect of alkaloids on the conformation of HSA was analyzed using circular dichroism (CD), UV/vis absorption, synchronous fluorescence and three-dimensional fluorescence spectra techniques.

The interaction between bovine haemoglobin and C.I. Solvent Red 24 was investigated by UV/vis absorption, fluorescence, resonance light-scattering spectra, synchronous fluorescence as well as three-dimensional fluorescence spectra techniques at pH 7.4. The dye effectively quenched the intrinsic fluorescence of bovine haemoglobin via static quenching. The process of dye to bovine haemoglobin was spontaneous, the related changes in enthalpy and entropy being 1.78 kJ mol−1, 81.58 J mol−1 K−1 respectively, according to the van't Hoff equation, indicating that hydrophobic interaction played a major role in stabilizing the complex. Synchronous fluorescence spectroscopy and three-dimensional fluorescence spectra showed that the structure of the tyrosine residue environments was altered by the dye which interacted at the α1β2 interface of the bovine haemoglobin molecule.

The interaction between human serum albumin (HSA) and pentachlorophenol (PCP) was investigated by UV/vis absorption, circular dichroism (CD), fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. PCP effectively quenched the intrinsic fluorescence of HSA via static quenching. The process of binding PCP on HSA was a spontaneous molecular interaction procedure. The hydrophobic interaction played a major role in stabilizing the PCP–HSA complex. The distance r between donor and acceptor was obtained to be 3.35 nm according to Forster’s theory. The binding site of PCP to HSA mainly located within hydrophobic cavity between domain II and domain I. The effect of PCP on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy, CD and three-dimensional fluorescence spectra.

The interaction between bovine hemoglobin (BHb) and Fe 3 O 4 colloid was investigated by UV/vis absorption, FT-IR, fluorescence, resonance light scattering spectra, CD, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. Fe 3 O 4 effectively quenched the intrinsic fluorescence of BHb via static quenching. The process of binding Fe 3 O 4 on BHb was a spontaneous molecular interaction procedure. The thermodynamic parameters indicate that van der Waals and hydrogen bonds, electrostatic interactions played a major role in stabilizing the Fe 3 O 4 –BHb complex. The effect of Fe 3 O 4 on the conformation of BHb was analyzed using CD and synchronous fluorescence spectroscopy.

The interaction between bovine hemoglobin (BHb) and phosphomolybdate acid (PMo 12 ) was investigated by UV/vis absorption, IR, circular dichroism (CD), fluorescence, resonance light scattering spectra, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. PMo 12 effectively quenched the intrinsic fluorescence of BHb via static quenching. The process of binding PMo 12 on BHb was a spontaneous molecular interaction procedure. The thermodynamic parameters, Δ H ° and Δ S ° were estimated to be 28.69 K J mol −1 , 158.20 J mol −1 K −1 according to the van’ Hoff equation. This indicates that hydrophobic interaction played a major role in stabilizing the PMo 12 –BHb complex. The effect of PMo 12 on the conformation of BHb was analyzed using synchronous fluorescence spectroscopy, IR and CD spectra.

The interaction between imidacloprid (IMI) and human serum albumin (HSA) was investigated using fluorescence and UV/vis absorption spectroscopy. The experimental results showed that the fluorescence quenching of HSA by IMI was a result of the formation of IMI-HSA complex; static quenching was confirmed to result in the fluorescence quenching. The apparent binding constant K(A) between IMI and HSA at three differences were obtained to be 1.51 x 10(4), 1.58 x 10(4), and 2.19 x 10(4) L mol(-1), respectively. The thermodynamic parameters, DeltaH degrees and DeltaS degrees were estimated to be 28.44 kJ mol(-1), 174.76 J mol(-1) K(-1) according to the van't Hoff equation. Hydrophobic interactions played a major role in stabilizing the complex. The distance r between donor (HSA) and acceptor (IMI) was obtained according to fluorescence resonance energy transfer. The effect of IMI on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy CD and three-dimensional fluorescence spectra, the environment around Trp and Tyr residues were altered.

The features of FeTCPc (Fe(III)-2,9,16,23-tetracarboxyphthalocyanine) binding to bovine serum albumin and bovine hemoglobin were investigated by fluorescence and UV/vis absorption spectroscopy. FeTCPc has the ability to quench the intrinsic fluorescence of both bovine serum albumin and bovine hemoglobin through mainly static quenching. The binding site number n , apparent binding constant K A and the corresponding thermodynamic parameters Δ G 0 , Δ H 0 , Δ S 0 at different temperatures were calculated; both electrostatic and hydrophobic interactions play a major role in stabilizing the complex. The distance r between the donor (bovine serum albumin or bovine hemoglobin) and acceptor (FeTCPc) was obtained according to fluorescence resonance energy transfer. The effect of FeTCPc on the conformation of the two donors was analyzed using synchronous fluorescence spectroscopy.

The interaction of benzidinne (BZ) with bovine hemoglobin (BHb) under physilolgical condition was studied by fluorescence spectrum. Fluorescence data revealed that the fluorescence quenching of BHb by BZ was the result of the formed complex of BZ–BHb, The quenching and energy transfer mechanisms were discussed, respectively. The binding constants and thermodynamic parameters at three different temperatures, the binding locality, and the binding power were obtained. The hydrophobic and hydrogen bonds interactions were the predominant intermolecular forces to stabilize the complex. The conformation of BHb was discussed by synchronous and three-dimensional fluorescence techniques.