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, ¹H NMR, and ¹³C 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 (σ_e) 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.     

Synthesis, <Emphasis Type="Italic">Spectrofluorometric</Emphasis> Studies,Micellization and non Linear Optical Properties of Blue Emitting Quinoline (AMQC) Dye

Blue emitting 2-amino-4-(3, 4, 5-tri methoxyphenyl)-9-methoxy-5,6 dihydrobenzo[f]isoquinoline-1-carbonitrile (AMQC) dye was synthesized by one-pot multicomponent reactions (MCRs) of 3,4,5-trimethoxybenzaldehyd, malononitrile, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one and ammonium acetate. Results obtained from spectroscopic and elemental analysis of synthesized AMQC was in good agreement with their chemical structures. Fluorescence polarity study demonstrated that AMQC was sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including electronic absorption, excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield were investigated in order to explore the analytical potential of AMQC. Dye undergoes solubilization in different micelles and may be used as a quencher and a probe to determine the critical micelle concentration (CMC) of SDS and CTAB. Nonlinear optical parameters of AMQC dye shows relatively lower nonlinear refractive index and nonlinear absorption coefficient at the power levels. Variation of n₂ with concentration is linear in the concentration range used in the present study.     

Green Synthesis,Spectrofluorometric Characterization and Antibacterial Activity of Heterocyclic Compound from Chalcone on the Basis of in Vitro and Quantum Chemistry Calculation

2-amino-4-(4-bromophenyl)-8-methoxy-5,6-dihydrobenzo[h]quinoline-3-carbonitrile (ABDC) was synthesized by the reaction of (2E)-2-(4 bromobenzylidene) - 6 -methoxy-3,4-dihydronaphthalen-1(2H)-one (Chalcone) with malononitrile and ammonium acetate under microwave irradiation. Chalcone was synthesised by the reaction 4-bromobenzaldehyd, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one under the same condition. Structure of ABDC was conformed by ¹H and ¹³C NMR, FT-IR, EI-MS spectral studies and elemental analysis. The electronic absorption and fluorescence spectra of ABDC have been studied in solvents of different polarities, and the data were used to study the solvatochromic properties such as excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield. The absorption maximum and fluorescence emission maximum was observed red shift when increase solvent polarity n-Hexane to DMSO. ABDC undergoes solubilization in different micelles and may be used as a probe and quencher to determine the critical micelle concentration (CMC) of CTAB and SDS. The anti-bacterial activity of chalcone and its cyclized product ABDC was tested in vitro by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria was determined with the reference of standard drug Tetracycline. Results showed that the ABDC is better anti-bacterial agent as compared to chalcone. The anti-bacterial activity was further supported by the quantum chemistry calculation.     

Novel luminescent hybrid materials by covalently anchoring 2-[3-(triethoxysilyl) propyl-1H-Benz [de]isoquinoline-1, 3(2H)-dione to bimodal mesoporous materials

We report on the synthesis of luminescent hybrid mesoporous materials (LHMS) by covalently anchoring 2-[3-(triethoxysilyl) propyl-1H-Benz [de]isoquinoline-1, 3(2H)-dione to bimodal mesoporous materials (BMMs) through postsynthesis methods. The resulting samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption/desorption isotherms, transmission electron microscopy (TEM), ²⁹Si NMR analysis, elemental analysis, and fluorescence measurements. The results revealed that luminescent organic molecules have been successfully introduced into the pore channels of BMMs without disrupting the structure, whereas the ordering degree of BMMs framework decreased after functionalization. The obtained materials (LHMS-10) showed excellent luminous performance, and the emission peak shifted to a lower wavelength in comparison with that of pure luminescent dyes (from 464 to 454 nm) because of the polarity of the silica matrix. And the amount of fluorescence molecule had some influence on the luminescence behavior, which was also investigated and discussed. It can be concluded that the fluorescence properties of the dye molecule can be controlled at will by the loading amount.     

A new coumarin laser dye 3-(benzothiazol-2-yl)-7-hydroxycoumarin

The electronic absorption, and emission spectra as well as fluorescence quantum yield of 3-(benzothiazol-2-yl)-7-hydroxycoumarin (BTHC) were measured in different solvents and are affected by solvent polarity (Δf). The deprotonation of BTHC by triethylamine is a reversible process. BTHC is relatively photostable, the quantum yield of photodecomposition (φ_c) was found to be 2×10⁻⁴ and 2.7×10⁻⁴ in EtOH and DMF, respectively. The fluorescence lifetimes of BTHC were measured in the absence and in the presence of molecular oxygen and were found to be 2.82 and 2.78 ns, respectively. BTHC acts as good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in ethanol and gives laser emission with maxima at 508 and 522 nm.     

Spectroscopic Physicochemical and Photophysical Investigation of Biologically Active 2-oxo-quinoline-3-carbonitrile Derivative

4-(2,3,4-trimethoxyphenyl)-8-methoxy-2-oxo-1,2,5,6 tetrahydrobenzo [h] quinoline-3-carbonitrile (TMTQ) dye was synthesized by one-pot multicomponent reactions (MCRs) of 2,3,4 trimethoxybenzaldehyd, ethyl cyanoacetate, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one and ammonium acetate under microwave irradiation. The structures of the synthesized compound was established by spectroscopic (FT-IR, ¹H–NMR, ¹³C–NMR, EI-MS) and elemental analysis. In addition, spectroscopic and physicochemical parameters, including electronic absorption, excitation coefficient, Stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield have investigated in order to explore the analytical potential of synthesized compounds. TMTQ dye undergoes solubilization in different micelles and may be used as a probe and quencher to determine the critical micelle concentration (CMC) of CTAB and SDS. In addition we extent of TMTQ anti-bacterial properties TMTQ was first tested in vitro by the disk 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 Tetracycline.     

Intramolecular energy and charge transfer in 5-(9-anthryl)-3-(4-nitrophenyl)-1-phenyl-2-pyrazoline

The absorption and photoluminescence of the newly synthesized 5-(9-anthryl)-3-(4-nitrophenyl)-1-phenyl-2-pyrazoline (AN PP) were investigated. The absorption is the absorption of anthryl moiety at about 325-400 nm, superimposed on the broader absorption of 3-(4-nitrophenyl)-1-phenyl-2-pyrazoline moiety peaked at 420 nm. On excitation at 420 nm, the fluorescence spectrum has only one emission band from the pyrazoline moiety. This emission band exhibits a larger red shift with an increase in the polarity of solvents. But on excitation at 365 nm, the fluorescence spectrum has two emission bands coming from the anthryl and pyrazoline moieties, respectively. The intensity ratio of the two bands is different in solvents of different polarity. It is concluded that photo-induced intramolecular energy transfer from the anthryl to pyrazoline moiety exists simultaneously with the charge transfer from N (1) to C (3) in the pyrazoline moiety in the excited state and both compete with each other.     

Localized excitation effects in (E,E)-2,5-<Emphasis Type="Italic">bis</Emphasis>[2-(4-N,N-dipropylaminophenyl) ethylenyl]-3,6-dimethylpyrazine and generation of its different forms in solution

Dipole moments of (E,E)-2,5-bis[2-(4-N,N-dipropylaminophenyl)ethylenyl]-3,6-dimethylpyrazine (VS365) quadrupolar dye in 1,4-dioxane and cyclohexane in addition to its instantaneous fluorescence spectra and fluorescence lifetimes in dichloromethane (pure and with added trifluoroacetic acid) were measured. Quantumchemical calculations show that the π − π conjugated system is localized in the flattest part of the molecule due to disorder in the ground-state geometry of the dye molecule and that this part is the one responsible for light absorption. The effect of localized excitation of the dye causes a considerable change in its dipole moment Δ^aμ. Various fluorescent forms of the dye that feature considerably spaced emission spectra and different fluorescence lifetimes originate by adding trifluoroacetic acid to the solution of oligophenylenevinylene in dichloromethane.     

Solvent and pH Effects on the Fluorescence of 7-(Dimethylamino)-2-Fluorenesulfonate

A novel water-soluble solvatochromic molecule, 7-(dimethylamino)-2-fluorenesulfonate (2,7-DAFS), was prepared by a three-step reaction from 2-nitrofluorene in good overall yield. The pH and solvent effects on the UV-VIS absorption and fluorescence spectra of 2,7-DAFS have been studied. Protonation of the dimethylamino group switches the absorption from intramolecular charge-transfer (ICT) to π → π* transition. The ground state pKa value of 2,7-DAFS was determined as 4.51. The fluorescence spectrum of the excited basic form, *(DAFS), shows a structureless single band with a large Stokes shift, whereas that of the acidic form, *(⁺HDAFS), exhibits a structured band with a small Stokes shift. The emission intensities of the basic and acidic forms versus pH/Ho plots show stretched sigmoidal curves and indicate that (1) the rate of deprotonation of *(⁺HDAFS) is comparable to the fluorescence decay of the species, and (2) the efficient proton-induced quenching of *(DAFS) fluorescence occurs. The pKa* was estimated as −1.7 from the fluorescence titration curve. The fluorescence maximum of *(DAFS) is blue-shifted as the polarity of solvent decreases. However, no clear dependency of the emission intensity and spectral half width, and thus fluorescence quantum yield, on the solvent polarity was revealed. It appears that the fluorescence sensitivity of 2,7-DAFS is 15 ∼ 25 times greater than the sensitivity of a widely utilized fluorescent probe, 5-(dimethylamino)-1-naphthalenesulfonate. This higher sensitivity, together with the ease of derivatization, would provide the fluorene-based fluorescent molecules significant advantages for a variety of applications.     

Photophysical parameters and laser performance of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP): A new laser dye

The spectral properties such as singlet absorption, molar absorptivity, emission spectra, fluorescence quantum yield and excited state lifetime of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP) have been determined in different solvents. DMAFP dye exhibits a large red shift in both electronic absorption and emission spectra as the solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation. A crystalline solid of DMAFP gives an excimer like emission at 566 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. The ground and excited state protonation constants of DMAFP are calculated and amounted to 1.71 and 8.3, respectively. DMAFP acts as a good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in chloroform, methylene chloride and dioxane and gives laser emission in the range 460–590 nm. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σ_e) and half-life energy (E_1/2) are calculated. The photoreactivity and net photochemical quantum yield of DMAFP in chloromethane solvents are also studied.     

Spectral behavior study of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone

The photophysical properties such as singlet absorption, molar absorptivity, fluorescence spectra, fluorescence quantum yield (?_f) and transition dipole moment (μ₁₂) of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone (DMAPAPP) have been studied in different media. DMAPAPP exhibits a large red-shift in both absorption and emission spectra as the solvent polarity increases, indicating a large change in dipole moment of molecule upon excitation. The fluorescence quantum yield depends on the nature of the solvent. The absorption and emission spectra of DMAPAPP in dioxane–water mixture are also studied. The effect of different type of surfactants to determine their critical micellar concentration (CMC) and the microemulsion effect on the electronic absorption and emission spectra of DMAPAPP are recorded. The effect of acidity on the electronic absorption and emission spectra of DMAPAPP is studied to determine the pK_a and pK_a^? values.     

A New Fluorescent Squaraine Probe for the Measurement of Membrane Polarity

The present study was undertaken to evaluate the sensitivity of newly synthesized squaraine dye 1 to the changes in lipid bilayer physical properties and compared it with the well-known dye 2. Partitioning of the dye 1 into lipid bilayer was found to be followed by significant increase of its fluorescence intensity and red-shift of emission maximum, while intensity of the dye 2 fluorescence increased only slightly on going from aqueous to lipidic environment. This suggests that dye 1 is more sensitive to the changes in membrane properties as compared to dye 2. Partition coefficients of the dye 1 have been determined for the model membranes composed of zwitterionic phospholipid phosphatidylcholine (PC) and its mixtures with positively charged detergent cetyltrimethylammonium bromide (CTAB), anionic phospholipid cardiolipin (CL), and sterol (Chol). The spectral responses of the dye 1 in different liposome media proved to correlate with the increase of bilayer polarity induced by Chol and CL or its decrease caused by CTAB. It was concluded that dye 1 can be used as fluorescent probe for examining membrane-related processes.     

Micellar effects on the molecular aggregation and fluorescence properties of benzazole-derived push-pull butadienes

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in dioxane-water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties (such as polarity and CMC) have been determined using both dienes as probes.     

Synthesis and spectroscopic investigation of a novel solvatochromic dye

Optical response of a novel dye has been studied in various media like neat and mixed binary solvents, aqueous SDS micelles and β-cyclodextrin (β-CD) nanocavities. Fluorescence parameters in pure and mixed binary solvents have been found to be sensitive to the nature of the microenvironment. The emitting state of the dye in protic solvent is different from that in aprotic solvents. In presence of cations (H⁺, Mg²⁺), the dye exists in two tautomeric forms at equilibrium in solution. The values of the equilibrium constant (K) and ΔH⁰ have been measured. Values of local dielectric constant (ε) and microviscosity (η) at the region of solubilisation of the dye in aqueous SDS micellar media have been found out. The dye has also been found to form complex with β-CD. The equilibrium constant and the energy of maximum fluorescence of the dye encapsulated by β-CD have been determined.     

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10⁻³ mol dm⁻³ of DEAC gives laser emission in the blue region on pumping with nitrogen laser (λ_ex=337.1 nm). The laser parameters such as tuning range, gain coefficient (α), emission cross section (σ_e), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl₄ at a wavelength of 366 nm. The values of photochemical yield (?_c) and rate constant (k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH₃CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.     

Synthesis of Novel Fluorescent Cyclohexenone Derivatives and their Partitioning Study in Ionic Micellar Media

An approach is demonstrated toward the synthesis of four novel cyclohexenone derivatives (CDs) via a convenient route of Michael addition of ethyl acetoacetate. The molecular structures of CDs were confirmed by means of FT-IR, ¹H NMR, EIMS, UV and also by X-ray single crystal structure analysis. CDs are strongly fluorescent compounds and their fluorescent spectra exhibits intense violet fluorescence. To model the binding to biological membranes the behavior of CDs in micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) and an anionic surfactant, sodium dodecylsulfate (SDS) has also been examined. The characteristics of partition and binding interactions of CDs with CTAB and SDS were investigated by UV-Visible and fluorescence spectroscopic techniques. Higher values of all mentioned interactions in case of CTAB, compared to SDS, indicate that there are greater interactions between the CDs and CTAB than with SDS.     

Synthesis of chalcone (3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one): advantage of sonochemical method over conventional method

In this work, an attempt was made to synthesize chalcone (3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one) by condensation of 4-fluorobenzaldehyde with 1-(4-methoxyphenyl)ethanone under basic conditions by using both conventional (NUS) and sonochemical (US) methods. A simple condensation reaction of 4-fluorobenzaldehyde and 1-(4-methoxyphenyl)ethanone using potassium hydroxide as a base was carried out for the study. The synthesized chalcone derivative was characterized for FTIR, NMR, elemental analyses and studied for XRD, PSM, TGA and SEM properties to evaluate its performance obtained under ultrasonic energy. It was observed that complete conversion to chalcone occurred in 10 min by sonochemical method and in 4h by conventional method. Also it was found that crystallinity of the US synthesized chalcone was found to be increased by 63% than that of NUS synthesized chalcone. Finally, it has been observed that chalcone synthesis using sonochemical method is an energy efficient technique over conventional method (almost 90% of energy saving).     

Characterization of a Solvatochromic Fluorophore: 1-(2,2-Dicyanovinyo)-2,5-Dimethoxybenzene (DCN-2,5-DMOB)

Absorption spectra and steady-state fluorescence emission spectra for l-(2,2-dicyanovinyl)-2,5-dimethoxybenzene in five solvents were determined. Although the absorption spectra demonstrate little solvatochromism, emission peaks show a red shift of roughly 90 nm between cyclohexane and methanol or acetonitrile, which appears to indicate charge transfer associated with a relaxed, as opposed to a vertical, excited state. Semiempirical gas phase AM1 calculations on this compound and the related unsubstituted 2,2-dicyanovinyl benzene indicate a dihedral twist of roughly 35° between the phenyl and the dicyanovinyl planes for both molecules in their ground states, as well as substantial polarity associated with the ground states of these compounds.     

Quantum-chemical study of structure and spectral properties of triphenylamine-rhodanine dye 2-(5-(4-(diphenylamine)benzylidene)-4-oxo-2-thioxothiazolidine-3-yl) acetic acid

The structure and optical properties of triphenylamine-rhodanine dye 2-(5-(4-(diphenylamine)benzylidene)-4-oxo-2-thioxothiazolidine-3-yl) acetic acid, which is used as a sensitizer for nanocrystalline TiO₂ solar cells, are studied based on the density functional theory. The nature of the absorption of this dye in the visible and near UV regions is discussed within the time-dependent density functional theory (TDDFT). The calculations of the vertical excitation energies of the dye molecule taking into account the effect of solvent reveal a strong positive solvatochromic effect compared to the calculations in the vacuum approximation. The IR absorption bands of this dye in the region of 600–1850 cm⁻¹ are completely interpreted.     

Red Emitting Monoazo Disperse Dyes with Phenyl(1H-benzoimidazol-5-yl) Methanone as Inbuilt Photostabilizing Unit: Synthesis,Spectroscopic, Dyeing and DFT Studies

Synthesis of three novel phenyl(1H-benzoimidazol-5-yl)methanone based fluorescent monoazo disperse dyes and their characterization by spectroscopic methods (¹H NMR, ¹³C NMR, IR and MS) are presented. Insertion of phenyl(1H-benzoimidazol-5-yl)methanone moiety bring about induced fluorescence properties and enhanced photostability as compared to the previously reported analogues (CI Solvent Yellow 14, 4-diethylamino-2-hydroxy-1-diazobenzene and 7-(diethylamino)-4-hydroxy-3-(phenyldiazenyl)-2H-chromen-2-one). Synthesized phenyl(1H-benzoimidazol-5-yl)methanone based dyes exhibited red-shifted absorption maxima (497–516 nm), high molar extinction coefficients and are emitting in the far-red region (565–627 nm). Moreover, naphthalene-comprising dyes showed negative solvatochromism while N,N-diethylamine comprising dyes showed positive solvatochromism and are in good agreement with solvent polarity graphs and the computed energy levels of highest occupied and lowest unoccupied molecular orbitals. Synthesised dyes have better photostability (light fastness) and sublimation fastness on dyed polyester and nylon compared to reported analogues. DFT calculated energies, electrophilicity index and Frontier Molecular Orbitals (FMO’s) enabled to evaluate the stabilities of azo and hydrazone forms of the dyes.