Plasmonic Surface of Metallic Gold and Silver Nanoparticles Induced Fluorescence Quenching of Meso-Terakis (4-Sulfonatophenyl) Porphyrin (TPPS) and Theoretical-Experimental Comparable.

Colloidal metallic nanoparticles have attracted a lot of interest in the last two decades owing to their simple synthesis and fascinating optical properties. In this manuscript, a study of the effect of both gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs) on the fluorescence emission (FE) of TPPS has been investigated utilizing steady-state fluorescence spectroscopy and UV-Vis spectrophotometry. From the observed electronic absorption spectra, there is no evidence of the ground state interaction between metallic Au NPs or Ag NPs with TPPS. On the other side, the FE spectra of TPPS have been quenched by both Ag and Au NPs. Via applying quenching calculations, Ag NPs showed only traditional static fluorescence quenching of TPPS with linear Stern-Volmer (SV) plots. On the contrary, quenching of TPPS emission by Au NPs shows composed models. One model is the sphere of action static quenching model that prevails at high quencher concentrations leading to non-linear SV plots with positive deviation. However, at low Au NPs concentrations, traditional dynamic quenching occurs with linear SV plots. The quantum calculations for TPPS structure have been obtained using Gaussian 09 software: in which the TPPS optimized molecular structure was achieved using DFT/B3LYP/6-311G (d) in a gaseous state. Also, the calculated electronic absorption spectra for the same molecule in water as a solvent are obtained using TD/M06/6-311G + + (2d, 2p). Furthermore, the theoretical and experimental results comparable to UV-Vis spectra have been investigated.

Spectroscopic Behavior and Photophysical Parameters of 2-(Acetoxymethyl)-6-(1,2,4-triazinylaminodihydroquinazolinyl)tetrahydropyran Derivative in Different Solid Hosts.

Optical and photophysical properties of 6-substituted-1,2,4-Triazine fluorescent derivative dye doped in silicate based sol-gel, homopolymer of methyl methacrylate (PMMA), and copolymer (MMA/diethylene glycol dimethacrylate) (DEGDMA) were investigated. The pores of different hosts and caging of the dye were found to effect on the parameters such as molar absorptivity, cross sections of singlet-singlet electronic absorption and emission spectra, excited state lifetime, quantum yield of fluorescence. The dipole moment of electronic transition, the length of attenuation and oscillator strength of electronic transition from So → S1 have been calculated. The dye was pumped with different powers using 3rd harmonic Nd: YAG laser of 355 nm and pulse duration 8 ns, with repetition rate 10 Hz. Good photo stability for dye was attained. After 55,000 pumping pulses of (10 mJ/pulse), the photo-stabilities were decreased to 53%, 48%, and 45% of the initial ASE of dye in sol gel, PMMA, and Co-polymer respectively. The dye in sol-gel matrix showed improvement of photo stability compared with those in organic polymeric matrices.

Spectral Behavior and Photophysical Parameters of Dihydrophenanthro[9,10-e][1,2,4]Triazine Derivative Dyes in Sol-Gel and Methyl Methacrylate Polymer Matrices.

This paper deals with the optical and photophysical properties of dihydrophenanthro[9,10-e][1,2,4]triazine fluorescent dyes doped in Silicate based sol-gel and homo-poly methyl methacrylate (PMMA). Solid hosts were found to effect on the optical and photophysical parameters such as molar absorptivity, cross sections of singlet-singlet electronic absorption and emission spectra, excited state lifetime, quantum yield of fluorescence. The dipole moment of electronic transition, the length of attenuation and oscillator strength of electronic transition from So → S1 have been calculated. The dyes were pumped with different powers using 3rd harmonic Nd:YAG laser of 355 nm and pulse duration 8 ns, with a repetition rate at (10 Hz). Good photostability for compounds 1 and 2 were attained. It was decreased to 49% & 54% and 46% & 40% of the initial ASE of dyes in sol gel and PMMA, respectively, after 55,000 pumping pulses at (10 mJ/pulse). The dyes in sol-gel showed improved photostability compared with those in organic polymeric matrices.

Spectroscopic Investigation and Photophysics of a D-π-A-π-D Type Styryl Pyrazine Derivative.

E,E-2,5-bis(3,4-dimethoxystyryl)pyrazine (BDSP)has been prepared by aldol condensation between 2,5-dimethypyrazine and 3,4-dimthoxybenzaldehyde and characterized by IR, 1HNMR, 13C NMR and X-ray crystallography.The electronic absorption and emission properties of BDSP were studied in different solvents. BDSP displays a strong solvatochromic effect of the emission spectrum that is reflected by large red shifts of its fluorescence emission maximum on increasing the solvent polarity, indicating a large change in dipole moment of BDSP upon excitation due to photoinduced intramolecular charge transfer (PICT). Excited state intermolecular hydrogen bonding affects the energy of emission spectrum and fluorescence quantum yield of BDSP dye. The dye solutions (1×10(-4) M) in DMSO, DMF, CH3CN and dioxane give laser emission in green region upon excitation by a 337.1 nm nitrogen pulse (λ=337 nm). The tuning range, gain coefficient (α), emission cross ­ section (σe) and half-life energy (E1/2) has been determined. Ground and electronic excited states geometric optimization were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond analysis complemented the ICT. BDSP dye displays fluorescence quenching by colloidal silver nanoparticles(AgNPs). The fluorescence data reveal that radiative and non-radiative energy transfer play a major role in the fluorescence quenching mechanism.

Fluorescence, Photophysical Behaviour and DFT Investigation of E,E-2,5-bis[2-(3-pyridyl)ethenyl]pyrazine (BPEP).

E,E-2,5-bis[2-(3-pyridyl)ethenyl]pyrazine (BPEP) has been prepared by aldol condensation between 2,5-dimethylpyrazine and pyridine-3-carboxaldehyde. It is characterized by IR, (1)H NMR, and (13)C NMR. The electronic absorption and emission properties of BPEP were studied in different solvents. BPEP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BPEP upon excitation. The dye solutions (1 × 10(-4) M) in CHCl3, EtOH and dioxane give laser emission in blue region upon excitation by a 337.1 nm nitrogen pulse (λ = 337 nm). The tuning range, gain coefficient (α) and emission cross - section (σe) have been determined. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond analysis complemented the ICT. The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and are proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BPEP in different solvents were correlated with the polarity of the elected solvents. BPEP dye displays fluorescence quenching by colloidal silver nanoparticles (AgNPs). The fluorescence data reveal that radiative and non-radiative energy transfer play a major role in the fluorescence quenching mechanism.

Photophysical Behavior and Computational Investigation of Novel 1,4-Bis(2-(2-Phenylpyrimido[1,2-a]Benzimidazol-4-Yl)Phenoxy)Butan (BPPB) Macromolecule.

A new macromolecule pyrimido[l,2-a]benzimidazole derivative named 1,4-bis(2-(2-phenylpyrimido[1,2-a]benzimidazol-4-yl)phenoxy)butan (BPPB) has been synthesized in accepted yield using microwave assistance. The new compound BPPB has been formed by the interaction of 3,3'-((butane-1,4-diylbis(oxy))bis(2,1-phenylene))bis(1-phenylprop-2-en-1-one) (3) with 2- aminobenzimidazole (4) in the presence of potassium hydroxide as a basic catalyst in dimethylformamide (DMF) under microwave radiation for 20 min. The chemical structure of this novel compound was elucidated by elemental and spectral techniques including: FT-IR, (1)H-NMR, (13)C-NMR and mass spectra. The electronic absorption and emission spectra of BPPB were measured in different solvents. BPPB displayed a solvatochromic effect of the emission spectrum that is reflected by red shifts of its fluorescence emission maxima on increasing the solvent polarity, indicating a change of electronic charge distribution upon excitation. BPPB crystalline solids gave excimer-like emission at 535 nm with a bandwidth of ca. 60 nm. Ground and excited states electronic geometry optimizations using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, complemented these spectral findings. The intramolecular charge transfer was investigated by natural bond orbital (NBO) technique.

Fluorescence Quenching of Perylene DBPI Dye by Colloidal Low-Dimensional Gold Nanoparticles.

The interaction of a perylene DBPI dye [N,N-bis(2,5-di-tert-butylphenyl)-3,4:9,10-perylenebis(dicarboximide)] with aqueous colloidal gold nanoparticles (AuNPs) was studied using steady state fluorescence quenching measurements. The Stern-Volmer quenching rate constant (Ksv) was calculated as ~2.2 × 10(8) and ~1.072 × 10(9) M(-1) in ethanol and ethylene glycol respectively. From fluorescence quenching data, the static quenching and energy transfer play a significant role in the fluorescence quenching of DBPI with AuNPs. The apparent association constant (Kapp) was calculated as ~1.4 × 10(9) (EtOH)and ~3.7 × 10(9) M(-1) (ethylene). Due to AuNPs interaction with DBPI, the average aggregated colloidal AuNPs size is increased from ~53.39 nm (before interaction) to ~94.12 nm (after interaction).

Fluorescence quenching N,N-bis(2,6-dimethylphenyl)-3,4:9,10-perylenetetracarboxylic diimide (BDPD) laser dye by colloidal silver nanoparticles.

The fluorescence quenching N,N-bis(2,6-dimethylphenyl)-3,4:9,10-perylenetetra-carboxylic diimide (BDPD) by colloidal silver nanoparticles (AgNPs) was studied in methanol and ethylene glycol by steady state fluorescence measurements. The Stern-Volmer quenching rate constant (Ksv) was calculated as 8.1 × 10(8) and 8.22 × 10(8) M(-1) in methanol and ethylene glycol respectively. Taking the fluorescence lifetime of BDPD in the absence of silver nanoparticles as 3.2 ns, the values of the fluorescence quenching rate constants (kq = Ksv/τ) are calculated as 2.54 × 10(17) and 2.56 × 10(17) M(-1) s(-1) in methanol and ethylene glycol respectively. From the data, fluorescence resonance energy transfer and / or electron transfer processes play a major role in the fluorescence quenching of BDPD by AgNPs in methanol and low concentrations of Ag NPs in ethylene glycol. The static quenching rate constant in ethylene glycol was calculated by modified Stern-Volmer equation as V = 8.86 × 10(9) M(-1). For dynamic quenching, the radius of quenching sphere volume r values were found to be 68.3 and 70.6 nm in ethanol and ethylene glycol, respectively. For static quenching in ethylene glycol the effective radius of quenching sphere action (kinetic radius) was calculated as r = 152 nm.

Structural and photophysical properties of (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) in different media.

The spectral and photophysical properties of a new chalcone derivative (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) containing donor-acceptor group has been synthesized and characterized on the basis of the spectral (IR, (1)HNMR & (13)C NMR) and X- ray crystallographic data. The effect of solvents on photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of DPNP have been investigated comprehensively. Significant red shift was observed in the emission spectrum of DPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state. The difference between the excited and ground state dipole moments (Δµ) were obtained from Lippert-Mataga and Reichardts correlations by means of solvatochromic shift method. The effects of medium acidity on the electronic absorption and emission spectra of DPNP were studied. The interaction of DPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of DPNP by Ag NPs.

Synthesis, Spectral Characteristics and DFT Studies of the New Dye 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) in Different Solvents.

The photophysical parameters such as electronic absorption spectra, molar absorptivity(ε), fluorescence spectra and fluorescence quantum yield (φf) of a new dye namely 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) were determined in different solvents. The electronic absorption are less sensitive to medium polarity. A bathochromic shift was observed in emission spectra(ca. 50 nm) upon increase of solvent polarity, which indicates that the singlet excited state (S1) of DMMF is more polar than the singlet ground state (So). Solid crystals of DMMF exhibit intense yellow fluorescence maximum at 550 nm with bandwidth equal 64 nm upon excitation at wavelength 365 nm. The change in dipole moment value (Δµ) was calculated by using the variation of Stokes shift with solvent polarizability (Δf) (Lippert - Mataga plot) and was found to be 7.22 and 5.5 Debye for higher and lower energy of So - S1 (π-π*) H-1 → L and So - S1 (π-π*) H → L, respectively. These results show that, the excited state is more polar than the ground state. The net photochemical quantum yields of photodecomposition of DMMF (φc) were calculated as 7.2 × 10(-5), 1.14 × 10(-4), 1.44 × 10(-4) and 2.11 × 10(-4) in different solvents such as MeOH, CH2Cl2, CHCl3 and CCl4, respectively. DFT/TD-DFT methods were used to study the geometric and electronic structures of DMMF in different solvents. A good agreement was found between the experimental and theoretical results.

Spectroscopic investigation, effect of solvent polarity and fluorescence quenching of a new D-π-A type chalcone derivative.

A new chalcone derivative 3-(1-methyl-1H-pyrrol-2-yl)-1-naphthalen-2-yl propenone (MPNP) with electron donor-acceptor group has been synthesized and characterized by IR, (1)HNMR, (13)C NMR and X- ray crystallography. Electronic absorption and emission spectra of MPNP have been studied in solvents of different polarity. A remarkable red shift was observed in the emission spectrum of MPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state and the transition involved are π-π* with charge transfer character. Lippert-Mataga and Reichardts correlations were used to estimate the change in dipole moments (Δµ); suggest that the emissive state of MPNP is of strong ICT character. Fluorescence quantum yield (ϕf) of MPNP was correlated with empirical solvent polarity parameter ET(30), and it is observed that ϕf increases with increase in solvent polarity of polar aprotic solvents and decrease in alcoholic solvents. The interaction of MPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state emission measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of MPNP by Ag NPs.

Investigation of spectroscopic behaviors of newly synthesized (2E)-3-(3,4-dimethoxyphenyl)-1-(2,5-dimethylthiophen-3-yl)prop-2-en-1-one (DDTP) dye.

This study introduced spectroscopic properties, physicochemical parameters, and polarity and photostability behaviors of a newly prepared chalcone dye. The chalcone dye, (2E)-3-(3,4-Dimethoxyphenyl)-1-(2,5-dimethylthiophen-3-yl)prop-2-en-1-one (DDTP), was synthesized by the reaction of 3,4-dimethoxybenzaldehyde with 3-acetyl-2,5-dimethythiophene. Results of FT-IR, (1)H-NMR, (13)C-NMR and elemental analysis were in conformity with chemical structure of newly prepared DDTP. Data of thermal gravimetric analysis revealed that DDTP has good thermal stability. Increases in fluorescence intensities of DDTP with cetyltrimethyl ammonium bromide (CTAB) were observed. In comparison of fluorescence intensities for DDTP with CTAB, reductions in fluorescence intensities for DDTP with sodium dodecyl sulphate (SDS) were observed under the same experimental and instrumental conditions. Moreover, Benesi-Hildebrand method was applied to determine stoichiometric ratios and association constants of DDTP with CTAB and SDS. The stoichiometric ratio and association constant obtained from Stern-Volmer plot strongly supported those obtained from Benesi-Hildebrand plot of DDTP with SDS. Physicochemical parameters, such as, singlet absorption, molar absorptivity, oscillator strength, dipole moment and fluorescence quantum yield of DDTP were also estimated. Fluorescence steady-state measurements ultimately displayed that DDTP has a high photostability against photobleaching. Fluorescence polarity study revealed that DDTP was sensitive to the polarity of the microenvironment provided by different solvents.

Eco-friendly synthesis and in vitro antibacterial activities of some novel chalcones.

Chalcone derivatives have been synthesized by reaction of 1-(2,5-dimethyl-furan-3-yl)-ethanone with corresponding active aldehyde in ethanolic NaOH in microwave oven. The structure of these compounds was established by elemental analysis, IR, 1H-NMR, 13C-NMR, and EI-MS spectral analysis. The anti-bacterial activity of these compounds was first tested in vitro by the disc diffusion assay against two Gram-positive and two Gram-negative bacteria, and then the minimum inhibitory concentration (MIC) was determined with the reference of standard drug Chloramphenicol. The results showed that pyrazol containing chalcone (compound 8) inhibited both types of bacteria (Gram-positive and Gram-negative) better than chloramphenicol.

Experimental and theoretical studies of linear and non-linear optical properties of novel fused-triazine derivatives for advanced technological applications.

Controlling photophysical properties is critical for the continued development of electroluminescent devices and luminescent materials. The preparation and study of novel molecules suitable as luminescent for the development of optoelectrical devices have recently received a lot of attention. Even though the as-triazine unit is a good building block for organic active substances, it is rarely used in this context. We created here novel bis-triazine derivative dyes in the far UV-Vis range by alkylation of triazine-thione derivatives with appropriate dibromo compounds. At the B3LYP/6-311**G(d,p) basis set, their optimal molecular structures were obtained. DFT technique confirmed that the new triazine derivatives are in noncoplanar with one of the two phenyl rings and the triazine plane rotating out by 102.09. Also, depending on the energy gap difference between HOMO and LUMO, some important parameters including chemical potential (π), electronegativity (χ), and chemical hardness (η) were calculated. The compounds may be readily polarized and have significant NLO characteristics, as seen by the tiny HOMO-LUMO energy gap. The calculated values for the polarizability (α) of the two new triazine derivatives have the range 6.09-10.75 × 10-24 (esu). The emission peaks seemed to move to the long-wavelength (redshift), with a rise in the fluorescence band, suggesting that the singlet excited state is more polar than the ground state. The influence of solvent polarity and the intermolecular charge transfer (ICT) processes are reflected in the photophysical properties of new fused triazine derivatives. These properties such as extinction coefficient, absorption and emission cross-sections, fluorescence quantum yield, fluorescence lifetime, oscillator strength, the dipole moment, radiative decay rate constant, the energy yield of fluorescence, and the attenuation length were assessed and discussed.

Laser performance and investigation of the optimal density functional and the dependence of the basis sets for (E, E)-2,5-bis (3,4-dimethoxystyryl) pyrazine (BDP) molecule.

This manuscript includes some photophysical parameters and some optical properties such as absorption and emission spectra of the (E, E)-2,5-bis (3,4-dimethoxystyryl) pyrazine (BDP) by applying sol-gel and copolymer matrices. The BDP molecular structure is incorporated in sol-gel matrix and copolymer of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA). In case of sol-gel matrix, the BDP molecular structure has higher quantum yield in addition to photostability maxima. The laser behavior of this molecular structure containing sol-gel matrix is good senior compared to copolymer one via using diode laser (450 nm) as pumping laser of power 160 mW. Also, the fluorescence profile of the BDP molecular structure is sensitized via using cadmium sulfide (CdS) quantum dots (QDs) by applying sol-gel host. The optimized structure of the BDP molecule is obtained via applying B3LYP/6-31G(d) level of theory. The electronic absorption and emission spectra of the BDP molecular structure in ethanol solvent were calculated using time-dependent density functional theory (TDDFT) at CAM-B3LYP/6-31G + + (d, p) level. The obtained theoretical results were compared to experimental ones.

Optical, photo physical parameters and photo stability of 6-Substituted-1, 2, 4-Triazine mono glucosyl derivative to act as a laser dye in various solvents.

The optical properties of a visible absorption range6-Substituted-1, 2, 4-Triazine mono glucosyl fluorescent derivative dye, such as absorption spectra, emission spectra in different solvents, were experimentally investigated. As well, some important photo physical parameters such as extinction coefficient (ε), cross-sections of the absorption (σa) and the emission (σe), quantum yield (фf), fluorescence lifetime, oscillator strength (f), the dipole moment (µ), decay rate radiative constant (kr), energy yield of fluorescence (Ef) and the length of attenuation Λ (λ) were assessed. The ground-state (µg) and excited-state (µe) dipole moments by solvatochromic correlations method were reported. The dye amplified spontaneous emission (ASE) of 2 × 10-4M with different input pumping energies of a continuous wave blue diode laser (λ = 450 nm) was studied. Photostability of dye was observed that was decreased to 53% of its initial energy by pumping with 100 mW of diode laser after exposure to 120 min.

Photophysical properties and semiempirical calculations of perylene-3,4,9,10-tetracarboxylic tetramethylester (PTME).

The spectral behavior and fluorescence quantum yield of perylene-3,4,9,10-tetracarboxylic tetramethylester (PTME) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity. The dye exhibits high fluorescence quantum yield and high photostable. Crystalline solid of PTME gives excimer-like emission at 530 nm. The laser activity of PTME has been investigated. The dye solution in N,N-dimethylformamide (DMF) gives laser emission around 480 nm upon excitation by 337.1 nm nitrogen laser pulse. The excitation energy transfer from 7-dimethylamino-4-methylcoumarine (DMC) to PTME has also has been studied and the value of energy transfer rate constant, k(ET), and critical transfer distance, R(0) indicate a Förster-type mechanism. The photodecomposition of PTME in chloromethane solvents has been also studied. We applied semiempirical MO calculations using (PM3 and ZINDO-CI) calculations to explain the geometric and electronic behaviors of the PTME molecule in both ground and excited states and make a correlation with the experimental observations.

Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies.

The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by (1)H NMR, (13)C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δµ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

Spectroscopic investigation, photophysical parameters and DFT calculations of 4,4'-(1E,1'E)-2,2'-(pyrazine-2,5-diyl)bis(ethene-2,1-diyl)bis(N,N-dimethylaniline) (PENDA) in different solvents.

A comprehensive investigation on the photophysics of a π-conjugated potential push-pull chromophore system 4,4'-(1E,1'E)-2,2'-(Pyrazine-2,5-diyl)bis(ethene-2,1-diyl)bis(N,N-dimethylaniline) (PENDA) has been carried out spectroscopically. The optical absorption and emission properties of this molecule have been studied in different solvents. The molecule PENDA shows strong solvatochromic emission upon changing the solvent polarity from nonpolar to polar; indicating that emission state is of intramolecular charge transfer (ICT) character. The solvent effect on the spectral properties such as singlet absorption, molar absorptivity, oscillator strength, dipole moment and fluorescence quantum yield of PENDA have been studied in detail. Lippert-Mataga and Reichardt correlations were used to estimate the difference between the excited and ground state dipole moments (Δµ). Ground and electronic excited states geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TDDFT), respectively, with the Gaussian 09 package. A solution of (8×10(-5) M) PENDA in THF, dioxane, CH3CN and CHCl3 gives laser emission when pumped by a nitrogen laser pulse (λex=337.1 nm) of 800 ps duration and 1.48 mJ pulse energy. PENDA dye displays fluorescence quenching by colloidal silver nanoparticles (Ag NPs) in ethanol. The fluorescence data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching mechanism.

Microwave assisted synthesis, spectroscopic studies and non linear optical properties of bis-chromophores.

Bis chromophores were synthesized by the terephthalaldehyde with (4-nitrophenyl) acetonitrile/(4-flurophenyl) acetonitrile under microwave irradiation. Bis-chromophores were obtained in good to excellent yields. The structures of bis-chromophores were established by FT-IR, (1)H NMR, (13)C NMR, EI-MS and elemental analyses. Physical chemical properties such as singlet absorption, extinction coefficient, stokes shift, oscillator strength and dipole moment, were investigated by UV-Vis and fluorescence spectroscopy measurements. Further we also measured the nonlinear refractive index and nonlinear absorption coefficients of these compounds using the single beam z-scan technique with a cw argon ion laser at 514.5 nm at different concentrations in DMSO solvent. The third order nonlinear susceptibility was estimated from these measurements and it shows high nonlinearity. The high negative refractive index makes these compounds suitable for optical limiting application.