Search

the individual contract 2020.00252. CEECIND and several projects PTDC/QUI- LA/P/0140/2020, LAQV-REQUIMTE (LA/P/0008/2020). LS4FUTURE Associated Laboratory (LA/P/0087/2020) Publisher Copyright: © 2023 The Author(s) The exploration of novel long-lived near-infrared (NIR) luminescent materials has attracted significant attention due to their applications in optical communications, anticounterfeiting, and bioimaging. However, these materials usually present low photoluminescence quantum yields and low photo- and chemical stability. Novel emitters that overcome these limitations are in demand. In this study, NIR emission was achieved using widely available, sustainable, and non-toxic materials through the synthesis of sulfur-doped zeolites, with different S/Cl ratios. With a combination of computational calculations (TD-DFT) and spectroscopic data, this emission was assigned to the radiative decay of excited triplet states of [S3]2- clusters, which resulted in a remarkably high Stokes shift (1.97 eV, 440 nm) and an average decay time of 0.54 ms. These new materials present high stability, external quantum efficiency of up to 17%, and a long-lived NIR emission, placing these compounds in a unique position to be used in applications demanding NIR emitters. publishersversion published

Hydrothermal assisted Zinc Oxide (ZnO)-polyphenol nanohybrid (NHs) have been synthesized using natural products. The formation of nanohybrid was confirmed by UV VIS spectroscopy, fluorescence spectroscopy, and time resolved fluorescence spectroscopy. The crystalline morphology and size distribution was studied by TEM analysis. The synthesized zinc oxide (ZnO) nanohybrid exhibited antioxidant property by exerting excellent DPPH free radical scavenging activity. Whereas, no ROS generation was observed against DCFH. No inherent cytotoxicity of the synthesized nanohybrid was observed on 3T3L1 adipocyte cells. The study further demonstrated a cytoprotective activity of the nanohybrid on H2O2 induced oxidative stress on 3T3L1 cells indicating the potential therapeutic activity of the synthesized ZnO-Polyphenol nanohybrid.

Here, Tagetes erecta leaves extract mediated silver nanopartices (te-SNPs) were synthesized. This synthesis process was simple, one step and eco-friendly. The te-SNPs were characterized by various spectroscopic instruments such as ultraviolet visible (UV–vis), Fourier-transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS) and Transmission Electron Microscopy (TEM) with energy Dispersive X-ray Spectroscopy (EDS). These te-SNPs showed the effective bactericidal activity against Escherichia coli and Staphylococcus aureus. The interaction of te-SNPs with human serum albumin (HSA) was evaluated by UV–vis absorption, fluorescence (FL), time resolved fluorescence (TRF), DLS and circular dichroism (CD) study. TRF and temperature dependant study suggested that the interaction process followed the dynamic quenching mechanism. The stern-volmer quenching constants (KSV) were obtained as 1.36 × 107, 1.51 × 107 and 1.94 × 107 M−1at 288, 298 and 308 K respectively. The thermodynamic parameters were also evaluated and this result suggested that the interaction was spontaneous, and the hydrophobic forces played the most important role for the interaction process. In addition, CD spectra proved minute alteration of secondary structure of HSA upon interaction with the te-SNPs.

In this paper, we fabricated NaYF4: Eu3+ nanocrystals via a facile hydrothermal approach. By a technique of in situ optical spectroscopy, the luminescence kinetics of the NaYF4: Eu3+ nanocrystals were real-time monitored by a confocal optical microscopy system. It is discovered that the most intense emission peak of Eu3+ ions is at 615 nm (5D0→7F2) that belongs to the electric dipole (ED) transition and its intensity is sensitive to the crystal environment. The 5D0→7F2 emission band could appear obvious stark-splitting phenomenon during the heat process of the nanocrystals at 1000 °C. The luminescence mechanism of NaYF4: Eu3+ nanocrystals is analyzed by Judd–Ofelt theory. The special spectroscopic properties of NaYF4: Eu3+ nanocrystals at high temperature could have an impact on the optical properties of trivalent lanthanide ion doped fluoride materials and associated applications. Furthermore, this finding may serve as a promising and powerful technique to better investigate the PL mechanism.

This communication reports the facile preparation of graphitic carbon nitride (g-C 3 N 4 ) from urea via pyrolysis approach. Microstructure and morphology of the prepared g-C 3 N 4 were studied by analytical techniques such as X-ray diffractometry and Scanning Electron Microscopy (SEM), respectively. Simultaneous thermo-gravimetric and differential thermal analysis confirms the thermal stability of the g-C 3 N 4 over a wide range of temperatures. Room temperature fluorescence spectroscopic investigation substantiates the existence of three emission centers in the g-C 3 N 4. The nanosecond level time resolved fluorescence study divulges the longevity of photogenerated charge carriers. The calculated intensity average lifetime value of the synthesized g-C 3 N 4 is 9.42 ns Steady state and time resolved fluorescence spectroscopic analyzes corroborate the potential applications of graphitic-C 3 N 4 in optoelectronic devices.

In this study, the structural and photophysical properties of 2-ethoxy-4-fluoro phenyl boronic acid (BA1) fluorescent compound was analysed using experimental spectroscopy, single crystal X-ray diffraction techniques and theoretical calculations were implemented using DFT and TD-DFT methods. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED). The calculated HOMO-LUMO energies shows charge transfer within the molecule and the transitions were predicted to be as п-п∗. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), UV–Vis absorption spectra and Non-linear optical properties were also studied using the same method and basis set. The BA1 compound has been tested for sugar sensing applications by absorption and emission spectroscopic analysis, to understand BA1 with sugars (D-glucose and D-fructose) complexes. The fluorescence measurements of BA1 at physiological pH 7.5, demonstrated a phenomenal quenching response to fructose and glucose molecules by having a decrease in fluorescence intensity with 3.5 fold and 1.3 fold for 0 M–0.5 M concentration of fructose and glucose, respectively, which shows strong sugar binding affinity. The association and dissociation constants were calculated by employing Stern-Volmer equation. The Job's plot and the mass spectroscopic analysis was carried to know the stoichiometry ratio of binding. The counterpoise correction method was implemented to calculate the complexation energy of the BA1-sugar complexes. The fluorescence life time of the molecule was measured in the presence and absence of sugars. The obtained lifetimes were in comparison with the theoretically calculated lifetimeusing PhotochemCAD. All these results showed that, BA1 can readily bind with sugars and could play an important role in carbohydrate sensing applications.

Present work reports on Cytochrome C (Cyt C) adsorption from solution and as sub-micron sized colloidal particles (pH 7.5) at fluid/solid interface. The colloidal particles from 2 methods ((method 1 freeze-thaw); (method 2-Decane/water interface)) have been characterized by UV–Visible spectroscopy, Static and Time resolved Fluorescence spectra and Circular dichroic spectroscopy. Morphology and size studies indicate that the colloids are solid and well-packed. Using Quartz crystal microbalance with dissipation, elastic compliance of the protein on quartz surface has been monitored. Properties of the protein from solution and as colloids assembled from method 2 are similar in elastic compliance (65.53 ± 1.2 and 73.5 ± 1.1 GPa−1 respectively) due to polar/non-polar interactions at the solid surface. For particles from method 1, irregular desolvation of water on the particle surface results in higher compliance (104.3 ± 1.3 GPa−1). Change in work of adhesion from contact angle profiles shows optimal adhesion for colloids from method 1 whereas the protein solution and as colloids from method 2, show subnormal adhesion. The work shows the role of extensive H-bonding with the hydrodynamically coupled water leading to a fluid like system in protein colloids from method 1 whereas those from method 2 behaved more like the pure protein adsorbing from solution.

This paper presents a new strategy for qualitative identification of scopoletin and scopolin in Erycibe obtusifolia Benth using time-resolved (lifetimes) fluorescence and quantitative analysis with chemometrics-assisted excitation-emission matrix (EEM) fluorescence. Due to the significant spectral overlapping among analytes and interference, the use of the more selective time-resolved fluorescence is proposed for qualitative identification in quality control of traditional Chinese medicine (TCM) for the first time. Using the strategy of combining EEM fluorescence with second-order calibration method, i.e. parallel factor analysis (PARAFAC), the simultaneous quantification of scopoletin and scopolin in the complex system of Erycibe obtusifolia Benth was achieved successfully. The predicted concentrations were compared with the values obtained using high performance liquid chromatography-coupled to fluorimetric detector (HPLC-FLD), and no significant differences between them were observed. Therefore, the proposed methods using time-resolved fluorescence for qualitative analysis and EEMs coupled with second-order calibration for quantitative analysis in TCM are comparable and provide a suitable alternative to the chromatography-based method.

The present paper deals with the photophysical and time resolved spectroscopic investigations performed on the pristine short chain dyad, (E)-4-(((9H-fluorene-2-yl)imino)methyl)-N,Ndimethylaniline (NNDMBF) and its nanocomposite forms with CQD or NCQD. The experimental results with dyad-CQD (or NCQD) demonstrate that more than 80% trans structure of the ground state dyad could be protected in the environment of CQD (or NCQD) even on photoexcitation. Formations of elongated trans- conformers show in favor of efficient energy-storage systems. The stability of extended conformation has been hinted to be due to combination of surface coverage and surface trap effects, the later process seems to be the dominating one.

We report on the enhancement effect of metal nanotriangles (NTs) on the photoluminescence and its time-resolved dynamics of tris(8-quinolinolato) aluminum (Alq3). Regularly arranged Al NTs arrays were fabricated on the quartz substrate by means of nanosphere lithography. The absorption peaks corresponded to the localized surface plasmon (LSP) resonance of Al NTs were observed within a visible light region, and it was significantly shifted towards longer wavelength as increasing refractive index of the covering medium. The typical resonance wavelength of LSP of Alq3/Al NTs fabricated with 350 nm-PSt beads was 600 nm. From the PL measurement 2.6-fold PL enhancement was observed in Alq3 with Al NTs at room temperature, whereas the 4.4-fold PL enhancement was observed for Ag NTs with same size. According to the time-resolved PL data, the coupling of LSP with the excitation light field mainly contribute to the observed emission enhancement for the Al NTs, whereas the emission enhancement by Ag NTs can be originated from the direct coupling of LSP and emission which was suggested from the large contribution of short lifetime component.

We report, synthesis of orange red light emitting Sm3+ activated BiOCl phosphors at relatively low temperature (400 °C) and shorter duration of 1 h. Rietveld refined results confirmed that all the compounds crystallized in the tetragonal structure with space group P4/nmm (No. 129). Functional group analysis were carried out by Fourier transform infrared (FT-IR) and Raman spectroscopy. The Photo-luminescent (PL) experiment results reveal that, an intense PL transition at 598 nm (4G5/2 → 6H7/2) corresponds to orange red emission at λex = 408 nm. The maximum emission intensity was observed for BiOCl: Sm3+ (3 mol%) phosphor, above this concentration quenching takes place due to charge exchange with neighboring Sm3+ ions. Time resolved fluorescence spectroscopic result reveals that, the decay curve is bi-exponential in nature and having long lifetime (τ = 0.58 ms). The obtained CIE and CCT values suggest that these phosphors having excellent color purity (∼90%) and low correlated color temperature. These results suggest that, Sm3+ activated BiOCl can be a potential red phosphor materials for WLEDs and other optoelectronics applications.

Monomeric zinc phthalocyanine has been studied as a promising active photosensitizer in photodynamic therapy against cancer, in which its aggregate form is non-active. This paper aimed to describe the monomer/aggregates equilibrium of zinc phthalocyanine in binary water/DMSO mixtures. To reach this aim theoretical calculation, electronic absorption, static and time-resolved fluorescence, and resonance light scattering was used. Zinc phthalocyanine shows a complex water dependence behavior in the mixture. At least three distinct steps were observed: (i) until 30% water zinc phthalocyanine is essentially in the monomeric form, changing to (ii) small slipped cofacial-aggregates around 30% to 40% water and finally to (iii) a staircase arrangement of large aggregates at higher water percent. The staircase arrangement is driven by the intermolecular coordination between the pyrrolic nitrogen lone-pairs and the central metal zinc. The water-Zn coordination governs the fluorescence quenching by a static mechanism. These results have direct relevance in the better understanding on the behavior of zinc phthalocyanine in vivo and when incorporated in drug delivery systems for clinical applications in photodynamic therapy.

Determination of primary/intrinsic electron transfer rate (ket = 1/τet, s−1) in bimolecular photoinduced electron transfer reactions (PET) in solution phase monitoring fluorescence quenching is a controversial issue, predominantly due to constraint imposed by diffusion, and measurement of rate of formation of transient intermediates, therefore primary electron transfer rate, was suggested (J. Phys. Chem. B 2015, 119, 11253 − 11261). Herein, we report electron transfer dynamic of excited 7-methylbenzo[a]pyrene (MBP) in acetonitrile (ACN) in presence of different aromatic amine donors from very low concentration to finally in neat donors to access intrinsic, diffusion free, rate constants of bimolecular PET by using steady state and femtosecond time resolved fluorescence and femtosecond transient absorption (fsTA) spectroscopy. It appears that in lower concentration of donors, diffusion control or stationary regime of ET, observed dynamics by time resolved fluorescence as well as transient absorption spectroscopy replicate to each other leading to determine the bimolecular quenching rates (kd, M−1 s−1) instead of primary or intrinsic ET rates. In very higher donor concentration or in neat donors, non-diffusive or intrinsic regime of ET, amalgamation of femtosecond time-resolved emission and fsTA studies along with global and target analysis determines the primary/intrinsic ET rates (ket) between excited MBP and studied donors which are one to two orders of magnitude larger than corresponding bimolecular quenching rate constants (kd) in ACN. Intrinsic electron transfer occurs with very high rate of ket (∼1011 s−1) and the process lies in Marcus normal region and back electron transfer occur very slow kbet (∼108 s−1), the process lies in Marcus inverted region.

In this work, steady-state and time-resolved fluorescence experiments on solvation of C153, C102, 4-ANMP and PRODAN fluorescent probes in BmimBF4 and BmimBF4/PC mixtures with a molar fraction of ionic liquid equal to 0.65 and 0.85 are reported. Quantum Chemistry calculations were performed to complete the experimental data interpretation. All the four studied probes exhibit similar solvation dynamics, with their average solvation times following the trend 4-ANMP

Heavy metal free and non-toxic semiconductor nanocrystals are the most interested segment of the current bio-nanotechnology. In the present paper, structural changes of human serum albumin (HSA) upon its interaction with InP/ZnS QDs coated with amphilic poly ethylene glycol was probed by employing multi-spectroscopic tools. Steady state and time resolved fluorescence studies implied formation of non-fluorescent complex between HSA and QDs resulting out of static quenching. Interestingly, temperature dependent fluorescence quantitative studies show that at higher temperatures these bioconjugates are unstable and static quenching mechanism turns towards dynamic quenching as QDs diffuses through excited state of HSA. Binding and synchronous fluorescence spectroscopic analysis show that QDs binds predominantly to Trp-214 residue in the HSA subdomain IIA with hydrophobic forces. Hence, observed blue shift of about 5 nm in PL spectra of HSA is the clear sign of conformational deformation as the Trp-214 residue gradually enters into hydrophobic microenvironment during its conjugation with QDs. Energy transfer efficiency (ET), transfer rate (KT) and critical transfer distance (R0) were all calculated for HSA and PEG-InP/ZnS QDs system from Forster resonance energy transfer (FRET) studies. Gibb's free energy, enthalpy and entropy obtained from temperature dependent fluorescence studies implied, HSA-InP/ZnS QDs bioconjugation is spontaneous, endothermic, entropy driven and is in accordance with the second law of thermodynamics. Hill coefficient (n ≅ 1) and binding affinities (kb) confirmed strong binding of HSA to QDs surface through ‘non-cooperative interactions’. Also, experimental result of FTIR spectra confirmed the adsorption of HSA onto the surfaces of PEG-InP/ZnS QDs. In addition these results proves that greener, heavy metal free and non-toxic semiconductor nanoparticle (PEG-InP/ZnS QDs) can potentially replace heavy metal and toxic QDs in biophysical fields like conformational studies of proteins.

Binding interactions between the drug Juglone (JUG) and Lysozyme (LYZ) have been explored in details from spectroscopic studies aided by in silico calculations. UV-Vis, steady state and time resolved fluorescence spectroscopic studies indicate the formation of LYZ-JUG complex in the ground state. Quenching of corrected fluorescence spectra of LYZ in presence of JUG at varied concentrations in different temperature range have been estimated from Stern-Volmer (SV) plots. Time resolved fluorescence spectroscopic studies confirm the mechanism of quenching to be of static type. Binding constant associated with the LYZ-JUG complex has been estimated from Scatchard plot. The number of binding sites, thermodynamic parameters and the modes of interaction are also estimated. Synchronous fluorescence spectra monitored at two discrete wavelength windows confirm the prominent role of Tryptophan residues towards quenching of fluorescence in LYZ. The circular dichroism (CD) spectra signify alterations in the population of α-helical content within the secondary structure of LYZ in presence of JUG molecules. REES of LYZ in the presence of JUG further signify definite impact of the drug JUG molecule on the Trp residues of the protein. The experimental observations are supported by in silico molecular docking and molecular dynamics simulations.

This work presents an overview of a novel spectroscopic tool: Energy Dispersive Inelastic X-ray Scattering (EDIXS) spectroscopy. By the application of EDIXS, the local chemical environment of an element of interest can be characterized in a variety of experimental conditions. EDIXS makes use of core-level resonant inelastic X-ray scattering (RIXS), taking advantage of the benefits of an energy dispersive detection system and multivariate methods for the data analysis. As result, the proposed methodology presents a fast acquisition, energy-scanning free experiments, low self-absorption effects and an objective interpretation of the data. In this review a first section providing an introduction to the evolution of RIXS and the development of the EDIXS methodology is presented. After that, a theoretical frame from two different approaches is offered, presenting several aspects of the RIXS spectrum features and letting glimpse the origin of the peak fine structure, key issue of this technique. Next, an explanation of the different multivariate methods used for the data analysis is provided. By the end, a set of experimental results obtained with EDIXS are revised, including several irradiation geometries and setups (as total reflection, grazing incidence and even confocal) for a variety of samples. A brief summary with further discussions regarding the advantages of the presented methodology, including future perspectives as its applicability to different X-ray sources, are giving closure to the paper.

Femtosecond time-resolved spectroscopy and frequency-comb spectroscopy have been individually developed to achieve better time and frequency resolutions, respectively. The two spectroscopic techniques have been developed for different systems, even though they use mode-locked laser in common. Recently, there was an interesting merge of the two techniques into a dual frequency-comb (DFC) spectroscopy, resulting in a new femtosecond spectroscopy with simple instrumentation and high data acquisition speed compared to conventional femtosecond spectroscopic techniques. By slightly detuning the repetition rates of two phase-locked frequency-comb lasers, both automatic time-delay scanning and parallel data recording with single point detectors are possible. Thus, we anticipate that the DFC spectroscopy would allow one to expand the application limits of the conventional femtosecond spectroscopic methods. In this Perspective article, we provide reviews of linear and nonlinear DFC spectroscopy theory and applications with a perspective on the development of coherent multidimensional frequency-comb spectroscopy.

Surpassing the Shockley–Queisser limit, which places an upper bound on solar conversion efficiency for a single p–n junction solar cell at slightly more than 30%, is one of the grand challenges in the field of solar-energy research. Singlet fission (SF) in molecular acenes, the molecular analog of multiple exciton generation (MEG), has the potential to initiate a game-changing advance in solar-energy conversion. SF allows singlet-excited states (S1) to be down-converted into twice as many triplet-excited states (T1).

Porphyrin cored polyepichlorohydrin (POR-PECH) dendritic polymer was identified as an efficient turn-off fluorescence probe for selective determination of cyanide ion in aqueous medium. The dendritic polymer showed strong red fluorescence at 656 and 718 nm which was quenched in the presence of cyanide ion. POR-PECH showed high selectivity towards cyanide ion over other relevant anions including Cl−, Br−, F−, I−, NO2−, NO3−, CH3COO−, SO32−, CO32−, SCN−, HCO3−, HPO42−, H2PO4− etc. The proposed sensor is highly selective, sensitive which showed quick response towards cyanide ion. The limit of detection of proposed method was found to be 1.2 μM which was admirably lower than the maximum allowed cyanide content in drinking water (1.9 μM) as recommended by WHO. Back folding of self assembled porphyrin cored PECH dendritic chains by the addition of cyanide ion caused the quenching of fluorescence. The time resolved fluorescence life time, FE-SEM image and DFT studies supported the quenching mechanism.

In this work, we report on the time resolved spectroscopy of amplified spontaneous emission (ASE) from the conjugated oligomer (CO) 9,10-Bis[(9-ethyl-3-carbazoyl)-vinylenyl]-anthracene (BECVA) only upon energy transfer from another oligomer 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). BECVA do not dissolve readily in tetrahydrofuran (THF) at room temperature, but completely dissolved when the temperature of the solution (THF & BECVA mix) was risen to 65 °C and remained dissolved even after cooling to room temperature. The process of heating and dissolving do not affect the performance of the CO. The heat-treated solutions were used to perform all experiments, unless mentioned. The absorption spectra indicated no aggregate formation upon increasing concentration, but the fluorescence spectra were very different for several concentrations of the solution, indicating the presence of the excimer. Pure BECVA in THF was pumped at various pump powers and concentrations. This produced only a broadband emission (from 500 to 750 nm) with a FWHM of 250 nm, which has potential applications in white light OLED. Next, we tried to produce ASE using the energy transfer process from a conjugated polymer (CP) poly (9,9-dioctylfluorenyl-2, 7-diyl) (PFO); however, this did not produce ASE, which could be due to the significant hindrance of the macromolecular PFO. The intensity of the BECVA spectra was enhanced with energy transform from PFO. The output was a broadband emission ranging from 400 to 750 nm (FWHM 350 nm). Finally, we added the oligomer BECV-DHF in solution (THF) to the BECVA solution at optimal pump power and concentration of donor (BECV-DHF), and the super-irradiant laser was produced from BECVA at 500 nm with a FWHM of 6 nm. The ultrafast dynamics of the BECVA solution under high pump power excitation and different energy donor (PFO and BECV-DHF) were extensively studied in this work. To the best of our knowledge, this is the first report of a CO that does not intrinsically produce ASE, but produces efficient ASE only via the energy transfer process by another CO.

Steady state and time resolved spectral properties of 7,8-benzoquinoline (7,8-BQ) have been reinvestigated in a series of organic solvents of different proticity, polarity and wide range of pH. The salient features of this work are the effect of hydrogen bonding in protonation reaction which is explored through its behaviour in water and strong hydrogen bond donating solvent (trifluoroethanol). Quantum yield and rates (radiative, non-radiative and excited state protonation) have been calculated and discussed. Irreversible diffusion controlled excited state proton transfer in water and faster excited state protonation in trifluoroethanol is observed.

A porous organic polymer with fluorene and triazine units (PTF), was synthesised through a simple cost effective method. The material was well characterised by FT-IR, solid state 13C NMR and X-ray photoelectron spectroscopic studies. Absorption spectrum indicated the electronic coupling between the two units in the polymer backbone. Experiments proved high thermal and chemical stability, and porous nature of the material. Luminescence of PTF was quenched, on the addition of ppb level concentration of nitroaromatic compounds. This was attributed to the photo induced electron transfer from the electron rich polymer backbone to the electron deficient nitro aromatic compounds. The observed superamplification effect in the fluorescence quenching was studied extensively by a series of ground state absorption, steady state and time resolved fluorescence experiments. Finally, the superamplified quenching was successfully assigned to static quenching by quenching sphere of action model. High value of static quenching constant of the order of 3.9 × 10 3 M−1, for picric acid combined with detection limit as low as 89 ppb envisages PTF as an effective chemosensor for nitroaromatic explosives.

This work explores the optical properties of amorphous silica (ASO) and gold incorporated silica (Au SiO2) prepared from Rice husk (RH) which is a biomass and also an environment waste. X-ray diffraction study shows the amorphous nature of prepared SiO2 and diffraction peaks related to gold for Au:SiO2 samples. Optical absorption study reveals the surface plasmon resonance (SPR) band centred at 525 nm. Photoluminescence (PL) study expose the light emitting nature of prepared SiO2 and Au:SiO2 at different excitation wavelengths. Variations in PL of SiO2 while incorporating Au is attributed to the structural modifications and metal enhanced fluorescence. Time resolved photoluminescence (TRPL) conducted at different excitation and emission wavelengths show the three exponential emission decay of SiO2 and Au:SiO2 samples.

We synthesize a novel prospective nanocomposite material for X-ray induced photodynamic therapy. ZnO:Ga core is coated by the SiO2 shell facilitating a functionalization by a photosensitizer, protoporphyrin PpIX layer. By steady-state and time resolved spectroscopy we confirm the presence of energy transfer between the core and the photosensitizer, an essential requirement to induce a cytotoxic effect. Using the commercial chemical probe we also demonstrate the ability of prepared ZnO:Ga@SiO2-PpIX nanocomposite to generate singlet oxygen. Presented results show that this nanocomposite can be considered as a good candidate for potential application in X-ray induced photodynamic therapy.

Photophysical properties of the ground and excited states of 1-naphthol-4-sulfonate (1NO4S), photoacid, are investigated in different solvents and cyclodextrin derivatives of different size and structure. Fluorescence decay traces of 1NO4S are well fitted to double exponential decay function in all solvents. The short-lived traces with higher amplitude were assigned to emission of the neutral form (ROH*), while the long-lived traces with low amplitude were assigned to emission of the anionic form (RO−*). The photophysical properties of 1NO4S were correlated with a number of solvent parameters such as the solvent polarity parameters E T N and the reaction field factor Δf. Three linear solvation energy relationships developed by Kamlet-Taft, Catalan, and Laurence et al. were employed to assess the effect of non-specific and specific interactions on the photophysical properties of 1NO4S. All three solvation energy relationships showed that the non-specific interactions mainly control the photophysical properties of 1NO4S while the contribution of the specific interactions are weak. Molecular encapsulation of 1NO4S by α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), methyl-β-cyclodextrin (Mβ-CD), 2-hydroxypropyl-β-cyclodextrin (HPβ-CD) in aqueous solution has been studied by steady state and time resolved fluorescence techniques. Steady state fluorescence measurements show 1:1 inclusion of 1NO4S with different cyclodextrin derivatives with an association constant of 7.9 ± 4.0, 59.6 ± 10.0, 0.4 ± 0.5, 169.8 ± 25.0, and 359.0 ± 20.0 M−1 for 1NO4S complexes with α-CD, β-CD, γ-CD, Mβ-CD or HPβ-CD, respectively following the fluorescence intensity changes of the anionic form (RO−*) at 435.0 nm. Association constants obtained following the fluorescence enhancement of the neutral form (ROH*) were the same as determined following fluorescence intensity decrease of RO−* at 372 nm. Data derived from time resolved measurements gave very close value for the association constants as determined from steady state fluorescence measurements.

Circular permutation fluorescent protein is a novel method to construct biosensors. The ratio of two excitation channels is employed to quantitatively calibrate the level of analysts. SoNar is one of them, which can be used to monitor cellular NADH/NAD+ levels. However, the 490 nm excitation channel of these biosensors is sensitive to pH environments, which is negative in real applications. In this work, we demonstrated that the fractional intensity ratio extracted from time-resolved fluorescence spectroscopy could be used to quantify NADH levels with one excitation (420 nm) and one emission channels. The 420-nm excitation channel was pH resistant. Comparing to average lifetime, the fractional intensity ratio had a 3.2-fold dynamic range, which was much wider than average lifetimes.

The results of spectral–temporal studies of the filament plasma emission in air with a time resolution of 2 ps were presented. The filament was created by laser radiation with pulse duration of 60 fs and wavelength of 940 nm. It was shown that a spectral composition of the filament plasma depended on the numerical aperture (NA). At NA > 0.035, the atomic and ion lines of oxygen and nitrogen dominate in the spectrum on the background of an intense continuous continuum in the visible region. Molecular lines of the second positive system of nitrogen and the first negative system of molecular ions appear in the spectrum for NA 0.03. In case of NA 0.01, the spectrum consists of only the molecular and ion lines of N 2 and N 2 + . The emission intensity maxima of these lines delay relative to the laser pulse. The atomic lines begin to glow per (80–100) ps after the laser pulse. The characteristic time of the luminescent lines decay at 1/e level for ions is 18 ps, for molecules is 27 ps, and for atomic lines is 20 ns. Rapid decrease in the intensity of molecular lines emission is due to the deactivation of the particles upper states by electrons. The formation of N 2 + ( B 2 Σ u + ) excited states is most likely through their N 2 + ( X 2 Σ g + ) ground state in the process of multiphoton absorption of pumping radiation by nitrogen molecules and subsequent their excitation by electron impact.

Photophysical studies of resorcinol based acridinedione (ADDR) dyes with a simple amino acid like glycine were carried out in water. Addition of glycine to photoinduced electron transfer (PET) based dye resulted in a fluorescence enhancement. Interestingly, addition of glycine to PET dye not only results in a fluorescence enhancement but a significant shift in the emission maximum towards the red region was observed. The fluorescence enhancement is attributed to the suppression of the PET process through space between the donor and the acceptor moiety of acridinedione dye ring structure. Both hydrogen-bonding along with hydrophobic interactions influences the excited state properties of ADDR dyes in the presence of glycine are elucidated by fluorescence spectral techniques. The existence of dye in two different environments is established from Time resolved fluorescence lifetime studies. The addition of glycine to non-PET dye does not influence the excited state properties clearly reveals that the PET process is influenced by the presence of glycine in water.

We study how time-dependent optical measurements of spectra, scattering, and imaging can be used to add to the understanding of heterogeneous reactions, compared to work performed using tools developed for homogeneous reactions. Using hydrogen peroxide disproportionation by potassium permanganate as a model reaction, we measure the entire spectrum over reaction time, enabling a clear and useful correlation analysis and assignment of chemical species in heterogeneous conditions. We measure time-dependent dynamic light scattering to study oxygen nanobubble product formation kinetics and equilibrium. We perform macroscopic video-rate reaction imaging and information-theoretic analysis to characterize reaction and transport contributions to the observed signal. To illustrate the differences arising from measuring sample subsets vs the entire system, we integrate stochastic and macroscopic numerical simulations of reaction-diffusion to study homogeneous and heterogeneous reaction conditions. We hope the tools presented here may help understanding other chemical reactions in heterogeneous conditions.

Antimicrobial infection has emerged as one of the principal health problems in the world that requires urgent effective prevention. In order to deal with this reality, antibacterial photodynamic therapy of photosensitizers such as IR820 is one of the most encouraging and innovative methodologies to combat bacteria-caused infections. However, their activity is limited due to low photostability, short circulation, and lack of targeted bio-distribution. Herein, we have developed a user-friendly and universal approach to overcome such limitations of cyanine dye IR820 by encapsulating it with zeolitic imidazolate framework-8 (ZIF-8) keeping its activity intact. The synthesized ZIF8-IR820 nano-MOFs are characterized using electron microscopic and optical spectroscopic techniques. Moreover, the formation of hybrids is confirmed from the charge transfer process obtained from time resolved fluorescence transient and first principles DFT based analysis. The ultrafast charge transfer dynamic enhances the red-light sensitive reactive oxygen species (ROS) production capability which is further catalyzed in acidic pH and DFT based calculation validates the experimental results. The enhanced ROS production of ZIF8-IR820 nano-MOFs makes it superior in NIR induced antibacterial activity. Overall, the study demonstrates a detailed physical understanding of photosensitizer encapsulated nano-MOF system which shows efficient NIR light induced photo-dose dependent antibacterial activity that can be beneficial for potential bacterial remediation.

Heterocysts are formed in filamentous heterocystous cyanobacteria under nitrogen-starvation conditions, and possess a very low amount of photosystem II (PSII) complexes than vegetative cells. Molecular, morphological, and biochemical characterizations of heterocysts have been investigated; however, excitation-energy dynamics in heterocysts are still unknown. In this study, we examined excitation-energy-relaxation processes of pigment-protein complexes in heterocysts isolated from the cyanobacterium Anabaena sp. PCC 7120. Thylakoid membranes from the heterocysts showed no oxygen-evolving activity under our experimental conditions and no thermoluminescence-glow curve originating from charge recombination of S2QA−. Two dimensional blue-native/SDS-PAGE analysis exhibits tetrameric, dimeric, and monomeric photosystem I (PSI) complexes but almost no dimeric and monomeric PSII complexes in the heterocyst thylakoids. The steady-state fluorescence spectrum of the heterocyst thylakoids at 77 K displays both characteristic PSI fluorescence and unusual PSII fluorescence different from the fluorescence of PSII dimer and monomer complexes. Time-resolved fluorescence spectra at 77 K, followed by fluorescence decay-associated spectra, showed different PSII and PSI fluorescence bands between heterocysts and vegetative thylakoids. Based on these findings, we discuss excitation-energy-transfer mechanisms in the heterocysts.

The objective of this work was to evaluate the efficacy of time-resolved and stationary fluorescence spectroscopic techniques in the detection of adulterations in Whey Protein Concentrate (WPC) powder, used in nutritional supplements. Adulterations were performed by the individual addition of caffeine, creatine and lactose in WPC in different levels (10%, 20% and 30% w/w). Samples were submitted to 275 nm excitation wavelength. Time-resolved fluorescence revealed that the adulterations changed the lifetimes of the tri-exponential decay curves obtained at 335 nm. The 30% adulterations demonstrated higher values of the mean emission lifetime, with caffeine treatment statistically significant. The fluorescence spectra showed an emission peak at approximately 335 nm with a broadband between 325 and 430 nm in the caffeine treatment. Euclidean distance analysis indicated the creatine and lactose treatments (10, 20 and 30% w/w) as similar to control WPC, while caffeine 20% and 30% treatments not. Hierarchical Cluster Analysis could differentiate all caffeine treatments from the other samples. Principal Component Analysis confirmed the differentiation of all adulterants from the control WPC. In general, the application of time-resolved fluorescence and stationary fluorescence spectroscopy techniques allowed the characterization and observation of differences among the samples, when allied to statistical tools.

Homogenous photocatalytic systems based on copper photosensitizers are promising candidates for noble metal free approaches in solar hydrogen generation. To improve their performance, a detailed understanding of the individual steps is needed. Here, we study the interaction of a heteroleptic copper (I) photosensitizer with an iron catalyst by time-resolved spectroscopy and ab initio calculations. The catalyst leads to rather efficient quenching of the 3MLCT state of the copper complex, with a bimolecular rate being about three times smaller than the collision rate. Using control experiments with methyl viologen, an appearing absorption band is assigned to the oxidized copper complex demonstrating that an electron transfer from the sensitizer to the iron catalyst occurs and the system reacts along an oxidative pathway. However, only about 30% of the quenching events result in an electron transfer while the other 70% experience deactivation indicating that the photocatalytic performance might suffer from geminate recombination.

The present work deals with experimental determination of steady state fluorescence anisotropies, fluorescence lifetimes and consequentially the rotational reorientation times of three large, nonpolar laser dyes that are modelled as prolate ellipsoids. Steady state and time resolved fluorescence spectroscopic measurements on Exalite 404 (E404), Exalite 417 (E417) and Exalite 428 (E428) dyes in series of alkane and alcohol solutions are discussed. All the three probes are observed to exhibit significantly shorter reorientation times in series of alcohols as compared to alkanes. The experimental results are explained in light of SED hydrodynamic and quasihydrodynamic theories. It is for the first time DKS theory is found to correctly predict the experimental results in alkanes with precision for all the three probes. Particularly in case of E417 DKS theory correlates exceptionally well with predictions of slip hydrodynamics. Interestingly, the largest probe (E428) being reported for the first time, exhibits slip behaviour in alkanes and alcohols; behaviour in higher alcohols as well as alkanes. This suggests the existence of nonhydrodynamic forces and speculates that the straightforward relation between the probe size and the nature of their behaviour may not be appropriate. Further, the nature and geometries of probes were fully explored and characterized using NBO and DFT studies employing Gaussian09 program. Optimized geometries, energy band gap and HOMO-LUMO levels were determined from DFT exchange-correlation function B3LYP with 6-311g basis set. Inter and intra hyper-conjugative interactions were estimated from NBO analysis. A very strong interactions between π(C19 C21) → π⁎(C24 C25), π(C1 C6) → π⁎(C2 C3) and π(C33 C34) → π⁎(C28 C30) with E(2) energies 21.44, 21.75 and 22.75 kcal/mol were observed for E404, E417 and E428, respectively. Electron occupancies and p-character were also determined for these molecules.

Photophysical properties of some 1-naphthol and 2-naphthol sulfonate derivatives and their efficiency as singlet oxygen photosensitizers in aqueous media are reported. The fluorescence emission is mainly from the deprotonated form (conjugate base) and their maxima cover the range of 433–529 nm. The fluorescence decay of these derivatives was found to be fitted with bi-exponential function with χ2 of about 1.0 ± 0.1 in all cases. Rate constants for oxygen quenching of the excited singlet states of these compounds in H2O are found to be (1.2 ± 0.2) × 1010 M−1 s−1 for the neutral form and much lower for the quenching of their conjugate bases. p K a values were found to be in the range 7.4–9.5 while p K a * are close to zero and about 3.3 for 2-naphthol and 2-naphthol-6-sulfonate using Forster equation and in the range of 1.4–3.0 using the fluorescence titration method obtained from the relative integrated fluorescence intensity. Singlet oxygen quantum yields photosensitized by these photoacids were reported in D2O and found to be in the range 0.13–0.35 for the sulfonated derivatives.

In aqueous medium, the guest-host interaction of 7-(diethylamino)coumarin-3-carboxylic acid N-succinimidyl ester (7-DCCAE) with cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) are very interesting. The interaction of 7-DCCAE with CB7 and CB8 have been investigated in a systematic way by different types of spectroscopic techniques such as UV–Vis spectroscopy, steady state and time resolved fluorescence emission spectroscopy, 1H-NMR along with thermodynamic approach by isothermal titration calorimetry measurement. We observed that the photophysical properties of the aqueous solution of 7-DCCAE are modulated in the presence of CB7 and CB8. We observed that 1:1 complex is formed between 7-DCCAE with CB7 and CB8. From ITC measurement, we obtained different thermodynamic parameters associated with host-guest complexation. We have drawn up the driving forces involved for the host-guest complexation from ITC measurement. By using density functional theory geometry and frequency of the 7-DCCAE-CBn complexes were optimized. We observed that both the complexation processes were exothermic in nature from ITC as well as from computational study.

A novel material showing aggregation induced emission (AIE) is developed by reprecipitation method using 9‑Anthraldehyde (9-AC), where Sodium dodecyl sulfate (SDS) was used as morphology directing agent. 1-dimension rod and 2-dimension elongated hexagon shaped morphology of 9-AC aggregates have been synthesized. Morphology of the materials was characterized using optical microscopy. Photophysical properties of the hydrosol were studied using UV–Vis, steady state and time resolved fluorescence emission techniques. Computation of second order Fukui parameter as local reactivity descriptor on each atomic center of the titled compound also substantiate that the neighboring 9-AC molecules are arranged in trans conformation in its aggregated structures and this is in conformity with the crystal structure of 9-AC. The ‘turn off’ fluorescence property of aggregated 9-AC has been utilized for selective detection of picric acid and the fluorescence quenching has been explained due to ground state complexation between 9-AC and picric acid. The observed detection limit of picric acid was found as low as 8.07 μM.

Some indolizines with phenanthroline skeleton derivatives have been investigated using steady state absorption, emission and time resolved fluorescence techniques. The effects of the substituents on the electronic absorption spectra and fluorescence emission have been demonstrated. The fluorescence decay curves exhibit one or two decay times. The emission lifetime measurements revealed values of 3–5 ns under the excitation with 370 nm. The quantum yield was also determined. The quenching process of emission using picric acid as quencher was characterized by Stern-Volmer plots. The phenanthroline derivatives 2 and 5 possess high efficiency for the detection of picric acid.

Fӧrster resonance energy transfer (FRET) between MoS2 and polyaniline (PANI) is explored by steady state and time resolved fluorescence spectroscopy in the present study and FRET based turn-on sensing of bovine serum albumin (BSA) is also demonstrated. The intense fluorescence of prepared MoS2 QDs is quenched by addition of PANI. Stern-Volmer plot suggests that the quenching is dynamic one. The observed quenching is explained by FRET mechanism also. The efficiency of energy transfer and rate of energy transfer are found to be increasing with increasing concentration of PANI. Time resolved fluorescence measurements show the reduction of lifetime components of MoS2 (donor) upon increasing concentration of PANI (acceptor). The quenched fluorescence of MoS2 in the presence of PANI is gradually recovered by addition of BSA at nM level which demonstrates turn-on BSA sensing.

The binding nature of amphiphilic drugs viz. promethazine hydrochloride (PMT) and adiphenine hydrochloride (ADP), with human hemoglobin (Hb) was unraveled by fluorescence, absorbance, time resolved fluorescence, fluorescence resonance energy transfer (FRET) and circular dichroism (CD) spectral techniques in combination with molecular docking and molecular dynamic simulation methods. The steady state fluorescence spectra indicated that both PMT and ADP quenches the fluorescence of Hb through static quenching mechanism which was further confirmed by time resolved fluorescence spectra. The UV-Vis spectroscopy suggested ground state complex formation. The activation energy (Ea) was observed more in the case of Hb-ADP than Hb-PMT interaction system. The FRET result indicates the high probability of energy transfer from β Trp37 residue of Hb to the PMT (r=2.02nm) and ADP (r=2.33nm). The thermodynamic data reveal that binding of PMT with Hb are exothermic in nature involving hydrogen bonding and van der Waal interaction whereas in the case of ADP hydrophobic forces play the major role and binding process is endothermic in nature. The CD results show that both PMT and ADP, induced secondary structural changes of Hb and unfold the protein by losing a large helical content while the effect is more pronounced with ADP. Additionally, we also utilized computational approaches for deep insight into the binding of these drugs with Hb and the results are well matched with our experimental results.

Femtosecond transient absorption (TA) spectroscopy combined with picosecond time resolved fluorescence (TRF) were used to reveal the fluorescence kinetics of graphene oxide (GO) in water, ethanol and water-ethanol mixtures. Size-independent fluorescence of GO were observed in water, and pH-dependent fluorescence spectra could be fitted well by a triple emission relaxation with peaks around 440 nm, 500 nm, and 590 nm respectively. The results indicate that polycyclic aromatic hydrocarbons (PAHs) linked by oxygen-containing functional groups dominate GO’s fluorescence emission. GO’s fluorescence quantum yield was measured to be 2.8% in ethanol but 1.2% in water. The three decay components fluorescence decay, as well as the transient absorption dynamics with an offset, confirmed this solvent induced fluorescence enhancement. GO’s Raman spectral signals showed that GO in ethanol has a smaller average size of PAHs than that of GO in water. Therefore, besides other enhancement effects reported in literatures, we proposed that solvents could also change the size of PAHs, resulting in a photoluminescence enhancement. Our experimental data demonstrates that GO’s quantum yield could be up to 2.8% in water and 8.4% in ethanol and this observation may help ones to improve GO’s photoluminescence efficiency as well as its applications in solution.

We report excitation dependent tunable emission property of MoS2 quantum dots (QDs) which can be applicable for enhanced energy transfer applications. Spectral overlap of fluorescence spectra of the prepared MoS2 QDs excited at different wavelengths with the absorption spectrum of Rhodamine 6G (R6G) shows the possibility of Forster resonance energy transfer (FRET) phenomena between MoS2 QDs and R6G. The calculated overlap integrals are found to be increased when the excitation wavelength is varied from 330 to 430 nm. Steady state and time resolved fluorescence measurements are carried out to study the FRET process between MoS2 QDs and R6G experimentally. The results show that the energy is transferred from MoS2 QDs (serve as a donor) to R6G (function as an acceptor). Enhancement in energy transfer efficiency and resonant energy transfer rate are found as a result of exciting at different wavelengths, which is attributed to the increased overlap integral as shown by the spectral overlap. The FRET between prepared MoS2 QDs and R6G at 330 and 430 nm excitation is used for glutathione sensing application.

A pilot study has been carried out to characterize human salivary protein to discriminate the normal subjects from patients with oral premalignant lesions and oral squamous cell carcinoma (OSCC) conditions, using the native fluorescence emission spectra at 280 nm excitation, the fluorescence excitation spectra for 350 nm emission and time resolved fluorescence decay kinetics of protein fluorescence in the saliva. A markeable difference in the spectral signatures between the saliva of normal subjects from oral premalignant lesion and OSCC conditions were observed in both fluorescence emission spectra at 280 nm excitation and the fluorescence excitation spectra at 350 nm emission maxima. The possible reasons for the altered spectral signature were may be due to the altered microenvironment of saliva and its constituents during the transformation of normal into oral premalignant lesion and OSCC conditions. Based on the observed spectral difference an attempt have been made to determine the statistical significance. The discriminant analysis for the fluorescence emission spectra at 280 nm excitation of saliva of normal subject and OSCC conditions provides 77.8% specificity and 86.6% sensitivity and the fluorescence excitation spectra of the same discriminates with 77.8% specificity and 86.8% sensitivity. The time resolved fluorescence decay kinetics were also confirmed the alteration in the spectral signature were due to the alteration in the microenvironment of saliva and its constituents.

Three derivatives of perylene diimide, namely N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (DT-PDI), N,N′-dipentylperylene-3,4,9,10-tetracarboxylic diimide (DP-PDI) and N,N′-bis(1-hexylheptyl)perylene-3,4,9,10-tetracarboxylic diimide (DH-PDI) differ in their side-chain substitution have been examined to study the effect of side-chain substituents on their optical properties and structural morphology. Due to the different side-chain, the self-assembly of these molecules results in totally different optical properties and structural morphologies, as confirmed from the steady-state absorption and fluorescence, time resolved fluorescence, and scanning electron microscopy (SEM) techniques. The collected results confirmed the formation of one-dimensional (1D) nanowires in the case of short linear side chain, chunky aggregates in the case of long linear substituted side chain, and zero-dimensional (0D) nanospheres with the branched substituted side chain.

Quantum dots (QDs) are well known for their optical properties which differ from those of bulk semiconductors. Herein, we have created an energy transfer platform that combines CdS QDs with a coumarin based dye C485 [7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one]. Spectroscopic studies of energy transfer between the dye donor and CdS QDs as acceptors reveal the occurrence of dynamic quenching. Analysis of the steady-state and time resolved fluorescence measurements of C485 in the presence of CdS QDs infers fluorescence resonance (Forster type) energy transfer (FRET) as responsible for the quenching phenomena. The energy transfer efficiency as well as energy transfer distance for the donor-acceptor pair is calculated using steady-state fluorescence method. Luminescence enhancement of CdS QDs play a critical role in device performance for solar applications and also in the field of biological applications.

Guanidinium salt solutions are one of the important electrolytes which have been extensively used for understanding the folding/unfolding mechanism of proteins. The structure of aqueous Gdm2CO3 has been controversial as some studies suggest that the hetero ion pairing takes place which leads to the aggregation whereas other studies does not support the idea of ion pairing. In this paper, we have used the steady state, time resolved fluorescence methods and density functional theory to understand the structure of guanidinium carbonate (Gdm2CO3) in terms of ion pairing as well as aggregation. The structure of the aqueous Gdm2CO3 has been controversial as some studies suggests that the Interestingly, Gdm2CO3 does not have any aromatic chromophore but it shows the broad visible fluorescence in the aqueous medium. Moreover, the fluorescence spectrum depicts a strong excitation dependent feature violating the Kasha's Rule. The concentration dependent emission, excitation, lifetime fluorescence along the density functional theory studies clearly suggests the formation of different size of aggregated clusters of Gdm2CO3 which causes the visible fluorescence of aqueous Gdm2CO3 violating the Kasha's rule.

Many aromatic organic molecules exhibit strong and characteristic fluorescence when excited with ultraviolet radiation. As laser excitation in the ultraviolet generates both fluorescence and resonantly enhanced Raman scattering of aromatic vibrational modes, combined Raman and fluorescence instruments have been proposed to search for organic compounds on Mars. In this work the time-resolved fluorescence of a suite of 24 compounds composed of 2–5 ringed alternant, non-alternant, and heterocyclic PAHs was measured. Fluorescence instrumentation with similar specifications to a putative flight instrument was capable of observing the fluorescence decay of these compounds with a sub-ns resolution. Incorporating time-resolved capabilities was also found to increase the ability to discriminate between individual PAHs. Incorporating time-resolved fluorescence capabilities into an ultraviolet gated Raman system intended for a rover or lander can increase the ability to detect and characterize PAHs on planetary surfaces.

The complexation behavior of reactive and nonreactive N-substituted 1-amino-5-isocyanonaphthalene (ICAN) derivatives was studied in the presence of Ag(I) ions by UV–vis, steady-state and time resolved fluorescence measurements. The effect of ligand, solvent and counterion is covered. The equilibrium constants were found to be K AgL ∼ 10 6 M −1 in dioxane and water. Complex formation results a significant, solvent dependent (30–59 nm) batochromic shift of the emission maximum. This shift is accompanied by a switch-off effect in the case of the unreactive ligands, while in the case of the acrylated derivative (ACAIN) significant intensity enhancement was detected. Based on spectroscopic results only 1:1 AgL complex could be detected in solution at low concentrations c AgL −4 M, while at higher concentrations pure 1:2 AgL 2 formed which was characterized by ESI–MS, IR and NMR methods The structure and optical behavior of the complexes are discussed based on high-level quantum chemical calculations. It is shown that the complexation of ACAIN can be used for the selective detection and quantification of silver(I) ions from aqueous media. In addition, the fluorescene switch-off in the case of MICAN yields a significant contrast enhancement in biolabeling applications as is shown on fixated HaCat cells.s

The nature of interactions between heme protein human hemoglobin (HHb) and gold nanoparticles of two different morphologies that is GNP (spherical) and GNS (star-shaped) have been investigated by using UV–vis absorption, steady state fluorescence, synchronous fluorescence, resonance light scattering (RLS), time resolved fluorescence, FT-IR, and circular dichroism (CD) techniques under physiological condition of pH ~ 7 at ambient and different temperatures. Analysis of the steady state fluorescence quenching of HHb in aqueous solution in the presence of GNP and GNS suggests that the nature of the quenching is of static type. The static nature of the quenching is also confirmed from time resolved data. The static type of quenching also indicates the possibility of formation of ground state complex for both HHb-GNP and HHb-GNS systems. From the measurements of Stern-Volmer (SV) constants KSV and binding constants, KA and number of binding sites it appears that HHb forms stronger binding with GNP relative to GNS. Analysis of the thermodynamic parameters indicates that the formation of HHb-GNP and HHb-GNS complexes are spontaneous molecular interaction processes (∆ G