Impact of tunable 2-(1H-indol-3-yl)acetonitrile based fluorophores towards optical, thermal and electroluminescence properties

Herein, we have synthesized 4,5-diphenyl-1H-imidazole and 2-(1H-indol-3-yl)acetonitrile based donor–π–acceptor fluorophores and studied their optical, thermal, electroluminescence properties. Both the fluorophores exhibit high fluorescence quantum yield (Φ_f = <0.6) and good thermal stability (T_d10 = <300 °C), and could be excellent candidates for OLED applications. Moreover, the ground and excited state properties of the compounds were analysed in various solvents with different polarities. The geometric and electronic structures of the fluorophores in the ground and excited states have been studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The absorption of BIPIAN and BITIAN in various solvents corresponds to S₀ → S₁ transitions and the most intense bands with respect to the higher oscillator strengths are mainly contributed by HOMO → LUMO transition. Significantly, the vacuum deposited non-doped OLED device was fabricated using BITIAN as an emitter, and the device shows electroluminescence (EL) at 564 nm, maximum current efficiency (CE) 0.687 cd A⁻¹ and a maximum external quantum efficiency (EQE) of 0.24%.

Herein, we have synthesized 4,5-diphenyl-1H-imidazole and 2-(1H-indol-3-yl)acetonitrile based donor–π–acceptor fluorophores and studied their optical, thermal, electroluminescence properties.

Spectroscopic investigation and computational studies on the interaction of Acriflavine with various estrogens

The fluorescence quenching of Acriflavine (AFN) by certain estrogens was examined in aqueous media by employing steady state and time-resolved fluorescence measurements. The absorption spectra of AFN change with significant bathochromic shift in presence of quencher molecules. The quenching behavior was examined by correlating the bimolecular quenching rate constant (k_q) with the free energy change (ΔG). The decrease in quenching rate constant depends on the increase in oxidation potential of quencher molecules. The fluorescence quenching experiments were carried out in different solvents of varying polarities and reveals the possibility of charge transfer quenching mechanism. Lifetime measurements indicate static quenching. The quenching behavior is addressed from bond dissociation enthalpy (BDE) calculations. The antioxidant activity of estrogen compounds were evaluated by deoxyribose oxidation assay.

Influence of Different Zeolite Frameworks on the Geometry of Platinum(II)tetraammine Complex

The structural changes in the guest platinum(II)tetraammine complex due to the steric and electronic interactions with the host zeolite frameworks LTL, MWW, and Y have been investigated using density functional theory calculations. It is observed that the square planar geometry of platinum(II)tetraammine complex has been distorted to nonplanar geometry when encapsulated in supercages of zeolite framework. The distortion is found to be higher in LTL than that in Y and MWW frameworks, without affecting the nature of the zeolite framework. Geometrical parameters, highest occupied molecular orbital and lowest unoccupied molecular orbital energies, global hardness, and softness were calculated to understand the distortion in the pores of the zeolite matrix. The most plausible active site of the complex was identified using the Fukui functions.

A Spectroscopic Approach with Theoretical Studies to Study the Interaction of 9-aminoacridine with Certain Phenols

The influence of phenols upon the fluorescence quenching of 9-aminoacridine (9-AA) was examined in acetonitrile solution by employing steady state and time-resolved fluorescence measurements. On increasing the concentration of quencher molecules the absorption spectra of 9-AA change with significant bathochromic shift. The fluorescence intensity of 9-AA change in presence of quencher molecules were measured at various temperatures as a function of the quencher concentrations. The observed bimolecular quenching rate constant (kq) depends on the nature and electronic effect of substituent present in the quencher molecules. The bimolecular quenching rate constant (kq) decreases on increasing the oxidation potential of quencher molecules. To examine the quenching behavior, kq values were correlated with the free energy change (ΔG). To get forthcoming in the quenching process, fluorescence quenching experiments were carried out in different solvents of varying polarities. The observed result suggest the involvement of charge-transfer quenching mechanism. Lifetime measurements support static quenching. Further, the radical scavenging potential is calculated from density functional theory (DFT) calculations to address the quenching behavior of the quencher molecules. DFT result reveals that electronic features are important in tuning the quenching ability of the quencher molecules and found to agree with the obtained experiment result.

Synthesis, characterization and binding interactions of amino acids coupled perylene diimides with colloidal doped and undoped TiO₂

Two sensitizers based on amino acids coupled with perylene moiety having absorption in the visible region have been designed and their interaction with doped and undoped TiO2 for the application of dye sensitized solar cells (DSSCs) has been studied. The synthesized compounds PDI-PA and PDI-AA were characterized using (1)H and (13)C NMR, Mass and FT-IR spectroscopic techniques. The optical properties and lifetime measurements of the sensitizers were analyzed using various solvents with different polarity. The solvatochromism effect was studied using Lippert-Mataga plot. The electrochemical studies of both dyes were investigated in DMF with various scan rate ranging from 200 to 1000 mV s(-1). Colloidal doped and undoped TiO2 was prepared and characterized by using absorption measurements. Binding ability of the sensitizers with the nanoparticles was studied through absorption, fluorescence quenching, cyclic voltammetry and FT-IR measurements. Results obtained from all the above analysis suggest the mode of quenching may be static. The binding constant values were calculated using Kamat-Fox equation indicates the binding behavior of the sensitizers with the nanoparticles. The fluorescence quenching was mainly attributed to electron transfer from the excited state of PDI's to the conduction band of colloidal semiconductors. The electron transfer mechanism was explained based on the Rehm-Weller equation as well as the energy level diagram.

Antibacterial potential of rutin conjugated with thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs)

Quantum dots not only act as nanocarrier but also act as stable and resistant natural fluorescent bio markers used in various in vitro and in vivo photolabelling and biological applications. In this study, the antimicrobial potential of TGA-CdTe QDs and commercial phenolics (rutin and caffeine) were investigated against Escherichiacoli. UV absorbance and fluorescence quenching study of TGA-CdTe QDs with rutin and caffeine complex was measured by spectroscopic technique. QDs-rutin conjugate exhibited excellent quenching property due to the -OH groups present in the rutin structure. But the same time caffeine has not conjugated with QDs because of lacking of -OH group in its structure. Photolabelling of E. coli with QDs-rutin and QDs-caffeine complex was analyzed by fluorescent microscopic method. Microbe E. coli cell membrane damage was assessed by atomic force (AFM) and confocal microscopy. Based on the results obtained, it is suggested that QDs-rutin conjugate enhance the antimicrobial activity more than the treatment with QDs, rutin and caffeine alone.

Investigation on the inclusion and toxicity of acriflavine with cyclodextrins: a spectroscopic approach

Acriflavine hydrochloride (AFN) is a prospective drug worn in the eradication of HIV1 infection. The toxicity and adverse side effects renders the potent drug to limits its usage. However, to overcome the dilemma we have aimed to select carriers with great complexation efficiencies in different cyclodextrins (CDs) of varying cavity size. The interaction of AFN with α, β and γ-CDs were investigated using absorption and steady state as well as lifetime measurements. From the obtained data it was found that AFN fits in the cavity of α and β-CDs but unable to form inclusion complex with γ-CD. The effect of quencher molecules during the inclusion phenomena of AFN with CDs was explored via steady state measurements. The nature of binding forces responsible for the inclusion of AFN with CDs was discussed by using thermodynamic parameters. Using Benesi-Hildebrand equation the stoichiometry of AFN with CDs was predominantly found to be 1:1. To get deeper in situ, the in vitro toxicity of AFN and its complexation product were probed by Artemia salina sp. The toxicity of AFN was reduced when complexed with α and β-CDs.

CdTe quantum dot as a fluorescence probe for vitamin B(12) in dosage form

We here report the CdTe quantum dot (CdTe QDs)-based sensor for probing vitamin B12 derivatives in aqueous solution. In this paper, simple and sensitive fluorescence quenching measurements has been employed. The Stern-Volmer constant (KSV), quenching rate constant (kq) and binding constant (K) were rationalized from fluorescence quenching measurement. Furthermore, the fluorescence resonance energy transfer (FRET) mechanism was discussed. This method was applicable over the concentration ranging from 1 to 14μg/mL (VB12) with correlation coefficient of 0.993. The limit of detection (LOD) of VB12 was found to be 0.15μg/mL. Moreover, the present approach opens a simple pathway for developing cost-effective, sensitive and selective QD-based fluorescence sensors/probes for biologically significant VB12 in pharmaceutical sample with mean recoveries in the range of 100-102.1%.

"Turn-on-off-on" fluorescence switching of quantum dots-cationic porphyrin nanohybrid: a sensor for DNA

In this article, we describe a new platform for probing double stranded DNA (dsDNA) by tracing the "on-off-on" fluorescence signals of quantum dots-cationic porphyrin utilizing fluorescence and synchronous fluorescence measurements. Electrostatic interaction between the negatively charged thioglycolic acid capped CdTe quantum dots (CdTe-TGA QDs) and positively charged porphyrin surfaces leads to drastic quenching (turning off) of the donor by an effective electron transfer process. Interestingly, after the addition of calf thymus DNA (CtDNA), the porphyrins peel off from the quantum dot surface and bind to dsDNA, resulting in the restoration of fluorescence intensity of quantum dots (turning on). Consequently, this can be utilized for the selective sensing of dsDNA via optical responses. Experimental results show that the increase in fluorescence intensity is proportional to the concentration of CtDNA within the range of 6.5 × 10(-9) M to 29.6 × 10(-8) M under the optimized experimental conditions. Furthermore, the peel off mechanism was confirmed by atomic force measurement.

Interaction of acriflavine with pyrimidines: a spectroscopic approach

The interaction of acriflavine with uracils was investigated by using spectroscopic tools viz., UV-Vis absorption, steady state and time resolved fluorescence measurements. The spectroscopic data were analyzed using Stern-Volmer equation to determine the quenching process. The bimolecular quenching rate constant (k(q)), binding constant (K) and number of binding sites (n) were calculated at different temperature from the relevant fluorescence data. The experimental results obtained from life-time measurement indicate that the quenching mechanism was static via the formation of ground state complex. The free energy change (ΔGet) for electron transfer process was calculated by Rehm-Weller equation. The existence of binding forces and the interactions of acriflavine with uracils were examined.

Studies on the inclusion behavior of 9-Aminoacridine into cyclodextrins: spectroscopic and theoretical evidences

9-Aminoacridine (9-AA) is an important attractive pharmaceutical drug employed as chemotheraptic agent for wound dressings. However, 9-AA possesses limited solubility and rapid metabolic decomposition renders this potential drug to limit its applications. Here we propose cyclodextrins (CDs) as a drug carrier to improve the bioavailability, solubility of 9-AA. The interaction between 9-AA and CDs (α-CD and β-CD) has been studied using UV-Vis absorption, steady state time resolved fluorescence, (1)H NMR and FT-IR spectroscopy techniques. The spectroscopic measurements show that 9-AA does not form stable complex with α-CD and also confirmed by DFT calculations. On the other hand, 9-AA forms inclusion complex with β-CD in a 1:1 stoichiometry ratio. Our DFT results suggest that 9-AA stabilizes inside the CD environment through hydrogen bonding that has unambiguously confirmed by AIM analysis. Thus our studies provide a useful insights in the development of Aminoacridine based drugs & its delivery through a suitable carrier like CDs.

Spectroscopic investigation on the interaction of 9-aminoacridine with certain dyes

The fluorescence quenching of 9-Aminoacridine (9-AA) by various dyes were probed in aqueous medium using steady state and time resolved fluorescence spectroscopic techniques. From these techniques, we had rationalized the interaction of 9-AA with various dyes via ground state complex formation. The binding constant (K) and number of binding sites (n) were calculated from the relevant fluorescence quenching data. The fluorescence emission of 9-Aminoacridine was quenched by the dyes through static quenching followed by the mechanism of energy transfer. The static quenching mechanism was confirmed by lifetime measurements. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS), were calculated by thermodynamic equations. The results showed that Van der Waals interaction or hydrogen bond formation played a major role in the binding of 9-AA with these dyes.

Influence of terminal substitution on structural, DNA, protein binding, anticancer and antibacterial activities of palladium(II) complexes containing 3-methoxy salicylaldehyde-4(N) substituted thiosemicarbazones

The variable chelating behavior of 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones was observed in equimolar reactions with [PdCl(2)(PPh(3))(2)]. The new complexes were characterized by various analytical, spectroscopic techniques (mass, (1)H-NMR, absorption, IR). All the new complexes were structurally characterized by single crystal X-ray diffraction. Crystallographic results showed that the ligands H(2)L(1) and H(2)L(4) are coordinated as binegative tridentate ONS donor ligands in the complexes 1 and 4 by forming six and five member rings. However, the ligands H(2)L(2) and H(2)L(3) bound to palladium in 2 and 3 as uninegative bidentate NS donors by forming a five member chelate ring. From this study, it was found that the substitution on terminal 4(N)-nitrogen may have an influence on the chelating ability of thiosemicarbazone. The presence of hydrogen bonding in 2 and 3 might be responsible for preventing the coordination of phenolic oxygen to the metal ion. The interaction of the complexes with calf-thymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an electrostatic binding mode of DNA has been proposed. The protein binding studies were monitored by quenching of tryptophan and tyrosine residues in the presence of complexes using Lysozyme as model protein. Antibacterial activity studies of the complexes have been screened against pathogenic bacteria such as Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. MIC50 values of the complexes showed that they exhibited significant activity against the pathogens and among them, 3 exhibited higher activity. Further, anticancer activity of the complexes on the lung cancer cell line A549 has also been studied.

An investigation on the fluorescence quenching of 9-aminoacridine by certain pyrimidines

The fluorescence quenching of 9-aminoacridine by certain substituted uracils in water was studied using absorption, steady state and time resolved measurements. The bimolecular quenching rate constants (k(q)), binding constant K and number of binding sites (n) were calculated based on the fluorescence quenching data. The free energy change (ΔG(et)) for electron transfer process was calculated by Rehm-Weller equation. From lifetime measurement we observed that the quenching was mainly due to static mechanism involving ground state complex formation.

Fluorescence Quenching of Phycoerythrin by Anthraquinone Dyes

Fluorescence quenching of phycoerythrin (PE) by a series of anthraquinone dyes has been investigated using steady state fluorescence technique in water medium. The dyes used were Uniblue, Acid blue 129, Alizarin and Alizarin red S. The quenching of PE was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear indicating the dynamic quenching. The quenching rate constants (k q) were calculated by using fluorescence data. The mechanism of quenching is discussed on the basis of quenching rate constants as well as the reduction potential of dyes. The electron transfer mechanism has been proved by the calculation of free energy change (ΔGet) by applying Rehm-Weller equation.

Interaction of anthraquinone dyes with lysozyme: evidences from spectroscopic and docking studies

The interaction between lysozyme and anthraquinone dyes such as Alizarin Red S, Acid blue 129 and Uniblue was studied using steady state, time resolved fluorescence measurements and docking studies. Addition of anthraquinone dyes effectively quenched the intrinsic fluorescence of lysozyme. Fluorescence quenching of lysozyme by dyes has revealed the formation of complex. The number of binding sites (n) and binding constant (K) for all the three dyes was calculated by relevant fluorescence quenching data. Based on Förster's non-radiative energy transfer theory, distance (r(0)) between the donor (lysozyme) and acceptor (dyes) as well as the critical energy transfer distance (R(0)) has also been calculated. The interaction between dyes and lysozyme occurs through static quenching mechanism as confirmed by time resolved spectroscopy. The conformational change of lysozyme has been analyzed using synchronous fluorescence measurement. Finally, docking studies revealed that specific interactions were observed with the residue of Trp 62.

Investigations on the photoinduced interaction of water soluble thioglycolic acid (TGA) capped CdTe quantum dots with certain porphyrins

The photoinduced interaction of TGA capped CdTe quantum dots (QDs) with porphyrins such as meso-tetrakis(4-sulfonatophenyl)porphyrin [TSPP], meso-tetrakis(4-carboxyphenyl)porphyrin [TCPP], meso-tetrakis (4-N-methylpyridyl)porphyrin [TMPyP] and meso-tetraphenylporphyrin [TPP] has been studied by using absorption, steady state and time resolved fluorescence spectroscopy. The QD surface was negatively charged due to thiol capping agent containing carboxylic group. Positively charged TMPyP interacts with QDs through charge transfer mechanism, negatively charged porphyrins (TCPP and TSPP) interacted through energy transfer mechanism and the neutral one (TPP) does not have any interaction. The Stern-Volmer constant, quenching rate constant, association constants, rate of electron transfer and energy transfer parameters were calculated from the fluorescence data. Effect of molecular structure has also been studied.

Fluorescence Quenching Study on Electron Transfer from Certain Amines to Excited State Triphenylpyrylium Ion (TPP+)

The fluorescence quenching of excited singlet state of 2,4,6-triphenylpyrylium tetrafluoroborate (TPPBF4 or TPP+), a very good electron acceptor by amines were investigated in a acetonitrile solution using steady state technique. The bimolecular quenching rate constants lie in the range 2.11–10.26 × 1010 M-1 s-1. The driving force (ΔGet) for electron transfer process was calculated from the oxidation potential of amines and the reduction potential of TPP+. The observed k q values correlated well with the driving force for the electron transfer reactions. Aromatic amines show higher k q than aliphatic amines. From the oxidation potential of amines and the quenching rate constant values, a mechanism involving photoinduced electron transfer from amines to excited state TPP is suggested.

Photoinduced Electron Transfer between Triphenylpyrylium Ion (TPP+) and Certain Phenols

The photoinduced interaction between triphenylpyrylium ion (TPP+) and certain phenols were studied in acetonitrile medium by using absorption, steady state and time resolved fluorescence spectroscopic methods. The quenchers used were phenol, o-aminophenol, o-cresol, o-hydroxyphenol, o-chlorophenol, salicylic acid and salicylaldehyde. Linear Stern-Volmer plots were obtained from both steady state and time resolved measurements and also the calculated values of bimolecular quenching rate constants (k q) were matched well. The free energy change (ΔG et) has been evaluated by using Rehm-Weller equation for the confirmation of electron transfer from phenols to TPP+ ion.

A Study on the Fluorescence Quenching of Eosin by certain Organic Dyes

The fluorescence quenching of Eosin by certain dyes has been investigated using steady state technique. The dyes used are Uniblue-A, Acid blue 129, Alizarin, Alizarin red S, Erichrome Black T, Tartrazine, Methyl orange, Methyl red, Acid orange 63, Congo red. The quenching was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear in the range of quencher concentration used [0−5×10− 5] M. The quenching rate constant (k q ) is in the range of 0.85–26.65×1012 M− 1s− 1. The quenching mechanism is discussed on the basis of the quenching rate constants as well as the reduction potential of the dyes. Rehm-Weller equation is applied for the calculation of free energy change (ΔGet).

Fluorescence Quenching of Xanthene Dyes by TiO2

The fluorescence quenching of xanthene dyes by TiO2 has been investigated using steady state technique. The dyes used are eosin, rhodamine B, rhodamine 6G. The quenching was found to obey Stern-Volmer equation and the corresponding Stern-Volmer plots were linear in the range of quencher concentration used [0–5 × 10--5] M. The quenching rate constant (k q) is in the range of 0.77–8.30 × 1012 M-1 s-1. This study reveals effective quenching of xanthene dyes with TiO2. The quenching of xanthene dyes followed electron transfer mechanism.

Fluorescence Quenching of Meso-Tetrakis(p-Sulfonatophenyl)Porphyrin (TSPP) by certain Organic Dyes

The fluorescence quenching of meso-tetrakis (p-sulfonatophenyl) porphyrin (TSPP) by certain anthraquinone and azo dyes has been investigated using steady state fluorescence technique. The dyes used were Uniblue-A, Acid blue 129, Alizarin, Alizarin red S, Erichrome Black T, Tartrazine, Methyl orange, Methyl red, Acid orange 63 and Congo red. The quenching was found to obey Stern-Volmer equation and the corresponding Stern-Volmer plots were linear. The quenching rate constant (k q ) is in the order of 0.19–6.08×1012 M− 1s− 1. This study reveals effective quenching of TSPP by organic dyes.