Photophysics of a Monoannulated Indigo: Intra- and Intermolecular Charge Transfer.

In the present work, the photoinduced charge-transfer (CT) behavior of 7-phenyl-6H-pyrido[1,2-a:3,4-b']diindole-6,13(12H)-dione (HCB) as a function of solvent polarity is reported by UV-vis absorption, steady-state and time-resolved fluorescence, and quantum chemical calculations. Calculated excited state energies of HCB at the B3PW91/6-31+G* level in vacuo and in solvents fulfill the energy requirements for singlet fission, which is the most promising path for the generation of highly efficient solar cells. The calculated potential energy curve for the compound reveals that the keto form is the predominant form in the ground state. Large bathochromic shifts in fluorescence with decreasing trends of quantum yield and lifetime indicate the occurrence of intramolecular CT from the indole bicycle to the indolinone moiety of HCB in highly polar solvents. The observed quenching of HCB fluorescence in different solvents without altering the spectral shape upon addition of a donor, triethylamine, is attributed to intermolecular CT, and it was examined in terms of the Stern-Volmer kinetics. The thermodynamics of photoinduced CT processes in HCB was analyzed using the measured photophysical data and cyclic voltammetric redox potentials via the Rehm-Weller equation. Analyses with the semiclassical Marcus theory suggest that both the CT processes fall under the Marcus normal region.

Examining pharmacodynamic and pharmacokinetic properties of eleven analogues of saquinavir for HIV protease inhibition.

HIV is one of the most lethal viral diseases in the human population. Patients often suffer from drug resistance, which hampers HIV therapy. Eleven different structural analogues of saquinavir (SQV), designed using ChemSketch™ and named S1 through S11, were compared with SQV with respect to their pharmacodynamic and pharmacokinetic properties. Pharmacokinetic predictions were carried out using AutoDock, and molecular docking between macromolecule HIV protease (PDB ID: 3IXO) and analogues S1 - S11 as ligands was performed. Analogues S1, S3, S4, S9 and S11 had lower binding scores when compared with saquinavir, whereas that of analogue S5 was similar. Pharmacokinetic predictions made using ACDilab2, including the Lipinski profile, general physical features, absorption, distribution, metabolism and excretion parameters, and toxicity values, for the eleven analogues and SQV suggested that S1 and S5 are pharmacodynamically and pharmacokinetically robust molecules that could be developed and established as lead molecules after in vitro and in vivo studies.

Examining structural analogs of elvitegravir as potential inhibitors of HIV-1 integrase.

Acquired immunodeficiency syndrome (AIDS) is a major health problem in many parts of the world. The human immunodeficiency virus-1 integrase (HIV-1 IN) enzyme has been targeted in HIV patients for therapy. Several integrase inhibitors have been reported, but only elvitegravir (EVG), a new-generation drug, is clinically approved for HIV treatment. In the present work, we investigated two structural analogs of EVG as potential inhibitors of the target molecule, HIV-1 IN. The ligand binding site on HIV-1 IN was identified using Q-SiteFinder, and the HIV-1 IN protein was docked with ligand (EVG and/or analogs) using AutoDock 4. The results suggest that Lys173, Thr125, and His171 are involved in enzyme-substrate binding through hydrogen bonds. Single mutations carried out at Lys173, viz. Lys173Leu (polar > nonpolar) and Lys173Gln (polar > polar), in chain B using PyMOL showed the mutants to have lower binding energy when docked with analog 2, suggesting it to be more stable than analog 1. In conclusion, the mutant HIV-1 IN can bind EVG and its analogs. The physicochemical and pharmacokinetic parameters also show analog 2 to be a promising molecule that can be developed as an alternative to EVG to help overcome the problem of drug resistance by HIV to this inhibitor. Analog 2 may be used as an HIV-1 IN inhibitor with similar potential to that of EVG. Further validation through wet-lab studies, however, is required for future applications.

The effect of polarity and hydrogen bonding on the electronic and vibrational structure of the salicylate anion in acetonitrile and water: implicit and explicit solvation approaches.

This study investigates the fluorescence quenching of the salicylate anion in water compared to acetonitrile (ACN) and the stability of its keto structure in ACN using DFT and TD-DFT methods at the 6-311++G(d,p) basis set. Computational simulations in implicit and explicit environments of ACN and water reveal the effects of solvent polarity and hydrogen bonding on enol [Od-H⋯Oa] and keto [Od⋯H-Oa] tautomerization, fluorescence quenching, and the spectral profile of the salicylate anion. Implicit solvation models show a barrier height of approximately 1.9 kcal mol-1 in ACN and 3.6 kcal mol-1 in water for enol-keto tautomerization in the ground state, with no barrier in the excited state, leading to an ESIPT reaction in both solvents, but only ground state proton transfer in ACN. Simulated absorption spectra for both enol and keto forms are similar in both solvents, while the emission spectrum is red-shifted in water. Explicit solvation studies indicate greater stabilization of the salicylate anion in water than in ACN, with a blue shift in absorption and emission spectra and varying oscillator strengths. Solvent molecule positioning affects enol-keto stabilization in the ground state, but only the keto structure is stabilized in the excited state. Simulated IR spectra in water show a blue shift in Od-H stretching frequency and increased water molecule vibrational frequencies, suggesting non-radiative excitation energy transfer from salicylate ions to water molecules via n → σ* intermolecular hydrogen bonding interactions. This mechanism explains the fluorescence quenching observed in water and results align with experimental data, indicating hydrogen-bonded keto form stabilization both in water and ACN.

Experimental and theoretical study of the distance dependence of metal-enhanced fluorescence, phosphorescence and delayed fluorescence in a single system.

Distance dependent singlet and triplet metal-enhanced emission of eosin from silica coated silver island films (SiFs) has been studied by steady-state and time resolved fluorescence techniques, along with theoretical finite difference time domain (FDTD) numerical simulations, to understand how the thickness of the dielectric coating surrounding silver nanoparticles fundamentally affects luminescence enhancement. Our findings suggest that the distance dependence of metal-enhanced phenomena such as fluorescence, phosphorescence and delayed fluorescence is underpinned by the decay of the electric near-field, and depending on the actual silver silica sample embodiment, one can see either decreased or enhanced luminescence. These results not only expand our current MEF thinking but also suggest that one may well be able to approximate plasmon-enhanced luminescence values.

Intense photoluminescence in CaTiO3:Sm3+ phosphors, effect of co-doping singly, doubly and triply ionized elements and their applications in LEDs.

In this work, Sm3+-doped and Sm3+/Li+/K+/Mg2+/Ba2+/Gd3+/Bi3+ co-doped CaTiO3 phosphors were synthesized by a solid-state reaction method at 1473 K. The phase of phosphors was identified to be orthorhombic with space group Pnma (62) by XRD measurements. The morphological properties of the prepared samples were studied by SEM measurements. The average crystallite and particle sizes were found to increase in the presence of modifiers and they follow the trend Li+ > Mg2+ > Gd3+ > K+ > Bi3+ > Ba2+. EDX measurements were used to verify the presence of Ca, Ti, O, Sm, K, Mg, Ba, Gd and Bi atoms in the prepared phosphor samples. The Sm3+ ion shows emission peaks at 564, 599 and 646 nm due to 4G5/2 → 6H5/2, 6H7/2 and 6H9/2 transitions upon 407 nm excitation, among which the peak situated at 599 nm has maximum emission intensity. Concentration quenching was observed above 2 mol% of Sm3+ ions in this host. However, the emission intensity of Sm3+ peaks can be enhanced using different modifier (Li+/K+/Mg2+/Ba2+/Gd3+/Bi3+) ions. It was found that the size (ionic radii) and charge compensation of the ion together play a dominant role. The enhancement is more after co-doping with smaller radius ions (Li+, Mg2+ and Gd3+), among which Li+ shows the largest enhancement. This is because ions of smaller size will be able to go closer to the activator ion and the charge imbalance causes a larger field. The CIE color coordinates, correlated color temperature (CCT) and color purity of the phosphors were calculated and show orange-red color emissions with a maximum color purity of ∼93% in the case of CaTiO3:2Sm3+/1.0Li+ phosphor. The lifetime value is increased in the presence of these ions. It is again maximum for the Li+ co-doped CaTiO3:2Sm3+ phosphor sample. Thus, the prepared phosphor samples are suitable sources for orange-red light.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications.

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED's and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303-483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED's and photodynamic therapy for the cancer treatment.

Molecular and Therapeutic Insights of Alpha-Lipoic Acid as a Potential Molecule for Disease Prevention.

Alpha-lipoic acid is an organic, sulfate-based compound produced by plants, humans, and animals. As a potent antioxidant and a natural dithiol compound, it performs a crucial role in mitochondrial bioenergetic reactions. A healthy human body, on the other hand, can synthesize enough α-lipoic acid to scavenge reactive oxygen species and increase endogenous antioxidants; however, the amount of α-lipoic acid inside the body decreases significantly with age, resulting in endothelial dysfunction. Molecular orbital energy and spin density analysis indicate that the sulfhydryl (-SH) group of molecules has the greatest electron donating activity, which would be responsible for the antioxidant potential and free radical scavenging activity. α-Lipoic acid acts as a chelating agent for metal ions, a quenching agent for reactive oxygen species, and a reducing agent for the oxidized form of glutathione and vitamins C and E. α-Lipoic acid enantiomers and its reduced form have antioxidant, cognitive, cardiovascular, detoxifying, anti-aging, dietary supplement, anti-cancer, neuroprotective, antimicrobial, and anti-inflammatory properties. α-Lipoic acid has cytotoxic and antiproliferative effects on several cancers, including polycystic ovarian syndrome. It also has usefulness in the context of female and male infertility. Although α-lipoic acid has numerous clinical applications, the majority of them stem from its antioxidant properties; however, its bioavailability in its pure form is low (approximately 30%). However, nanoformulations have shown promise in this regard. The proton affinity and electron donating activity, as a redox-active agent, would be responsible for the antioxidant potential and free radical scavenging activity of the molecule. This review discusses the most recent clinical data on α-lipoic acid in the prevention, management, and treatment of a variety of diseases, including coronavirus disease 2019. Based on current evidence, the preclinical and clinical potential of this molecule is discussed. Supplementary Information: The online version contains supplementary material available at 10.1007/s43450-023-00370-1.

Evaluation of binding of potential ADMET/tox screened saquinavir analogues for inhibition of HIV-protease via molecular dynamics and binding free energy calculations.

Developing novel drug molecules against HIV is a scientific quest necessitated by development of drug resistance against used drugs. We report comparative results of molecular dynamics simulation studies on 11 structural analogues of Saquinavir (SQV) - against HIV-protease that were earlier examined for pharmacodynamic and pharmacokinetic properties. We reported analogues S1, S5 and S8 to qualify the ADMET criterion and may be considered as potential lead molecules. In this study the designed molecules were successively docked with native HIV-protease at AutoDock. Docking scores established relative goodness of the 11 analogues against the benchmark for Saquinavir. The docked complexes were subjected to molecular dynamics simulation studies using GROMACS 4.6.2. Four parameters viz. H-bonding, RMSD, Binding energy and Protein-Ligand Distance were used for comparative analyses of the analogues relative to Saquinavir. The comparison and analysis of the results are indicative that analogues S8, S9 and S1 are promising candidates among all the analogues studied. From our earlier work and present study it is evident that among the three S8 and S1 qualify the ADMET criterion and between S1 and S8, the analogue S8 shows more target efficacy and specificity over S1 and have better molecular dynamics simulation results. Thus, of the 11 de novo Saquinavir analogues, the S8 appears to be the most promising candidate as lead molecule for HIV-protease inhibitor and is best suited for testing under biological system. Further validation of the proposed lead molecules through wet lab studies involving antiviral assays however is required.Communicated by Ramaswamy H. Sarma.

Spectral and time domain fluorescence spectroscopy of gentisic acid molecule in protic and aprotic polymer matrix.

In the present work, the effect of polymer microenvironment on the photophysics of gentisic acid molecule [2,5-dihydroxybenzoic acid] (GA), steady-state and time-domain fluorescence measurements at different pH conditions were carried out in protic [polyvinyl alcohol PVA] and aprotic [polymethyl methacrylate (PMMA)] polymer matrices. Change in the proticity of the microenvironment of the polymer traps different ionic species along with the neutral form of rotamer P and R conformers of GA molecule, are found to be responsible for the change in the spectral, multi-exponential decay behaviour. In protic polymer, the appearance of a single emission band indicates, dissociation of the GA molecule is very high, and it present as a monoanion along with hydrogen-bonded P and R rotamers. However, in the basic polymer film, most of the conformers of R converted to the anion. In contrast, protonation slows down the dissociation of both P and R forms in the acidic film. Unlike PVA matrix, in PMMA, dual emission band appears due to slow dissociation of GA molecule and hydrogen-bonded rotamer P, and R form exists with monoanion species. The magnitude of large stokes shifted red emission due to excited-state intramolecular proton transfers (ESIPT) found grater in rotamer P compared to its anionic species (green emission) and a blue emission corresponds to rotamer R.

Förster Resonance Energy Transfer between Fluorescent Organic Semiconductors: Poly(9,9-dioctylfluorene-alt-benzothiadiazole) and 6,13-Bis(triisopropylsilylethynyl)pentacene.

In the present study, an investigation of the electronic excitation energy transfer between two p-type fluorescent semiconductors, F8BT [poly(9,9-dioctylfluorene-alcohol-benzothiadiazole] and TIPS-P [6,13-bis(triisopropylsilylethynyl)pentacene], has been carried out in a chloroform solution using steady-state and time-domain fluorescence techniques. The spectral overlap integral between donor (F8BT) emission and acceptor (TIPS-P) absorption is 2.04 × 1015 nm4/(M cm), and the corresponding critical transfer distance is 53.12 Å. In donor decay dynamics, at the lower acceptor concentrations, the observed results deviate from the Förster theory due to the combined effect of diffusion and energy migration. However, it does not exhibit energy migration and distribution for higher acceptor concentrations, and the system follows the Förster model of resonance excitation energy transfer (FRET). The higher value of the donor-acceptor interaction strength than self-interaction (donor-donor interaction) appears to be responsible for this behavior. Further, in acceptor decay, the appearance of the rise time and its decrease with the acceptor concentration confirms FRET from F8BT to TIPS-P.

Synthesis, characterization and photoluminescence study of novel sulfobetaine polyelectrolytes.

A novel sulfobetaine copolymer is developed via polycondensation approach. The comonomers, melamine, condenses with a diketone, 5,5-dimethyl-1,3-cyclohexane (dimedone) to produce polyimine chain based on Schiff base chemistry. Dimedone-[N,N' melaminium] propane sulfonate copolymer crystals were obtained on treatment of the polyimine with sulfopropylating agent, 1,3-propane sultone with a crosslinker, di(ethylene glycol diacrylate) (DEGDA). This crosslinked sulfobetaine polymer yielded fine needle like single crystals and shows strong blue fluorescence and a week green phosphorescence. Multi-exponential fluorescence decay function indicates the presence of different conformers both in solution and crystalline phase. This easy straightforward protocol for synthesis of crystalline, soluble, and luminescent polymer could prove to be a landmark in development of next generation smart functional materials.

Reinvestigation of the photophysics of 3-aminobenzoic acid in neat and mixed binary solvents.

The present study elucidates the reinvestigation of the photophysical behavior of 3-aminobenzoic acid (3ABA) in solvents of different polarities using the steady-state spectroscopic techniques. Kamlet-Taft and Catalan solvatochromic models have been used to analyze the solvatochromic changes in neat solvents. The hydrogen bond donating ability of the solvent was found to be the main parameter affecting the spectral behavior of 3ABA. The solvatochromic characteristics of 3ABA have also been examined in binary solvent mixtures viz. acetonitrile (ACN)-methanol (MeOH) and benzene (BEN)-MeOH using the concept of preferential solvation. The preferential solvation of 3ABA shows unusual behavior for BEN-MeOH binary mixture and described unnoticed sigmoidal behavior in the ground state and synergistic impact in the excited state. Besides, the 3ABA was studied theoretically by quantum chemical calculations using (HF) Hartree-Fock and (DFT/B3LYP) density functional theories and its electronic absorption bands have been assigned by time-dependent density functional theory (TD-DFT). The effect of solvents on 3ABA was considered using a IEF-PCM-TDDFT (integral equation formalism of the polarizable continuum model- TDDFT) method. Thus, the theoretical results were found to be closer to the experimental results.

Excited-State Dynamics of Quinine Sulfate and Its Di-Cation Doped in Polyvinyl Alcohol Thin Films Near Silver Nanostructure Islands.

The present study demonstrates the near-field effect of silver nanostructure island films (SNIFs) on the photophysics and exited-state dynamics of quinine sulphate (QS) and its di-cation (QSD), doped in polyvinyl alcohol (PVA) films. The results indicate a nearly 3.8-fold enhancement in absorption and 4000-fold enhancement in fluorescence in SNIF-coated QS-doped PVA films, whereas only twofold enhancement in absorption and sevenfold enhancement in fluorescence intensity are found in SNIF-coated QSD-doped PVA films. However, an increase in photostability and a decrease in decay time have been observed in both the SNIF-coated films as compared to their uncoated forms. Further, a decrease in the magnitude of the edge excitation red shift in emission spectra along with a red shift in the La band and a rise in the intensity of the Lb band of excitation is observed in SNIF-coated QSD films because of strong coupling of the Lb band with the surface plasmons of silver nanoparticles. Moreover, X-ray photoelectron spectroscopic measurement of silver nanoparticle-coated QS-PVA films shows no change in 3d3/2 and 3d5/2 transitions of silver, whereas the decrease in energy in these silver transitions in the QSD-PVA system is observed as compared to silver nanoparticle-coated PVA films. These results indicate the formation of a field-governed radiating plasmon and plasmon-coupled unified fluorophore system, respectively. This affects the photophysics of both of the molecules by plasmonic coupling of the Frank-Condon state, solvent relaxation state, and charge-transfer state by different orders of magnitude.

Effect of polymer microenvironment on excitation energy migration and transfer.

Excitation energy transfer between the dye pair acriflavine (donor) to rhodamine-6G (acceptor) in various polymers [polyvinyl alcohol (PVA), cellulose acetate, and polymethyl methacrylate (PMMA)] was studied using steady-state and time-resolved fluorescence spectroscopy at room temperature. In all these polymers, at higher acceptor concentrations, direct energy transfer from acriflavine to rhodamine-6G followed the Förster theory, which is indicated by the agreement in the values of the observed critical transfer distance with that calculated from spectral overlap. On the other hand, at low acceptor concentrations, the excitation energy migration influences the kinetics, resulting in a significantly higher value of the observed critical transfer distance, which is explained on the basis of Loring et al. (Loring, R. F.; Anderson, H. C.; Fayer, M. D. J. Chem. Phys. 1984, 80, 5731-5744) and Huber (Huber, D. L. Phys. Rev. B: Condens. Matter Mater. Phys. 1979, 20 2307-2314) theories. It was observed that the spectral overlap for donor-donor transport (excitation migration) and donor-acceptor transfer (energy transfer) and thereby other energy transfer parameters were influenced by the microenvironment of the polymers. The efficiency of energy transfer (eta) was the highest in PMMA and the lowest in PVA. Further, the study of acceptor dynamics under energy transfer showed that the rise time of the acceptor also depends on the nature of the polymer microenvironment.

Photoinduced proton transfer coupled with energy transfer: Mechanism of sensitized luminescence of terbium ion by salicylic acid doped in polymer.

In the present work, excited state intramolecular proton transfer (ESIPT) in salicylic acid (SA) monoanion and subsequent sensitization of Tb(3+) ion in polyvinyl alcohol (PVA) have been studied. The study has been carried out both by steady state and time domain fluorescence measurement techniques at room temperature. It is found that the SA completely ionizes and exists as monoanion in PVA. It exhibits a large Stokes shifted blue emission (10 000 cm(-1)) due to ESIPT and shows a decay time of 6.85 ns. On the other hand, Tb(3+) ion shows a very weak green emission and a decay time of approximately 641 mus in PVA film. Upon incorporating Tb(3+) ion in SA doped PVA film, both intensity and decay time of SA decrease and sensitized emission from Tb(+3) ion along with 3.8 mus rise time is observed. Energy transfer is found to take place both from excited singlet as well as triplet states. A brief description of the properties of the present system from the viewpoint of luminescent solar collector material is addressed.

Detection and monitoring of in vitro formation of salicylic acid from aspirin using fluorescence spectroscopic technique and DFT calculations.

Acetylsalicylic acid commonly termed as aspirin (AS) is a well known antipyretic and anti-inflammatory drug which can also be used to reduce death risks due to heart attack. In addition to this, it also exhibits some adverse effect such as gastrointestinal, tinnitus, Reye's syndrome. The side effects of AS such as gastrointestinal ulcer, tinnitus and Reye's syndrome are caused due to conversion of AS into its active metabolite salicylic acid (SAL). Conversion of AS into SAL has been investigated generally at basic pH. Since the pH of Gastrointestinal tract is on average neutral ranging from 6.5-7.4. Therefore in the present research work, in vitro conversion of AS to SAL was detected at neutral pH in both aqueous medium and human blood serum samples by time series fluorescence measurements and DFT study. The SAL obtained from AS at neutral pH was observed to be stable for ~ 6 and ~ 4 days in aqueous medium and blood serum, respectively. The mechanism of conversion of AS into SAL was investigated using the transition state theory employing density functional theory (DFT). On the basis of DFT calculation the in vitro formation of SAL from AS at neutral pH was found to involve two intermediate transition states.

QPRTase modified N-doped carbon quantum dots: A fluorescent bioprobe for selective detection of neurotoxin quinolinic acid in human serum.

Highly fluorescent nitrogen doped carbon quantum dots (NCQDs) were synthesized using microwave assisted green method. It was characterized by Transmission Electron Microscopy (TEM), FTIR, UV-Visible absorption and Photoluminiscence (PL) techniques. The NCQDs were immobilized with an enzyme named quinolinate phoshphoribosyl transferase (QPRTase). The NCQDs immobilized by QPRTase was used as a fluorescent bioprobe for the selective detection of endogenous neurotoxin quinolinic acid (QA) whose elevated level in serum is marker of many neurological disorders such as Alzheimer's, Huntington's and HIV associated dementia (HAD) as well as deficiency of vitamin B6. Steady state PL studies were carried out to measure the PL response of the fabricated fluorescent bioprobe as a function of QA concentrations in human serum samples. This probe was found applicable in linear range [3.22-51µM] with the limit of detection ~ 6.51µM. It has desirable sensitivity ~ (0.02340±0.0001) µM-1, excellent stability for ~ 7 weeks and good reproducibility. The similar response of this fluorescent bioprobe for QA detection in triple distilled water and human serum shows that it is unaffected by variation in media. Hence, this fluorescent bioprobe can be employed for QA detection in serum sample for the early detection of many diseases.

Photo-induced relaxation and proton transfer in some hydroxy naphthoic acids in polymers.

Photophysical and photochemical properties of 3-hydroxy-2-naphthoic acid [3,2-HNA] and 1-hydroxy-2naphthoic acid [1,2-HNA] in different aprotic, protic, and ion exchange (Nafion) polymers have been described in this article. In both molecules, intramolecular hydrogen bond (IMHB) exists between OH and COOH functional groups. Both 3,2-HNA and 1,2-HNA form different emitting species in different polymeric media. Fluorescence characteristic of 3,2-HNA is found to depend on its concentration, nature of the microenvironment, and wavelength of excitation, while 1,2-HNA is less susceptible to these changes. 3,2-HNA exhibits dual fluorescence band (normal and large Stokes shifted) in aprotic and only a single large Stokes shifted fluorescence in protic polymers, while 1,2-HNA shows a single fluorescence band along with weak phosphorescence emission in these polymers. Both excited-state inter and intramolecular proton transfer (ESPT) take place in 3,2-HNA in aprotic and protic polymers, resulting in large Stokes shifted emission band. A competition between ESIPT and excimer formation is observed by the appearance of rise time on increasing the concentration of 3,2-HNA in protic polymer. In Nafion film, 3,2-HNA is present as a cationic as well as neutral species. The presence of extra protons in Nafion film facilitates excited-state intramolecular proton transfer (ESIPT) in the neutral species of 3,2-HNA and gives large Stokes shifted emission (10 500 cm(-1)). No such effect is observed in 1,2-HNA doped in Nafion film. It is observed that, depending on the position of the IMHB ring, the electronic spectra get modified and the strength of IMHB is affected by the micro-environment of the polymer which alters the photophysics of these molecules.