Study of novel fluorescent coumarin-3,4-dihydropyrimidin-2(1H)-ones dyads. Estimation of ground- and excited-state dipole moments from a solvatochromic shift

Release of dissolved organic matter from wetland plants and its interaction with polycyclic aromatic hydrocarbons

Dissolved organic matter (DOM) derived from wetland plants played a critical role in CWs pollutant migration. This study investigated the character and release pattern of DOM derived from two wetland plants, Phragmites australis and Cladophora sp., and the interaction between DOM with phenanthrene (PHE), benzo(a)pyrene (Bap), and benzo [k]fluoranthene (BkF) under different physical conditions were also studied using spectroscopic techniques. DOM release was related to plant species and withering stage. Humic acid (HA)-like fractions (C3 and C5) were dominated in P. australis (52%) and completely withered Cladophora sp. groups (55%), while protein-like fractions (C1 and C2) dominated in early withered Cladophora sp. groups (52%). Due to the cell and tissue structure difference among plants and their withering stage, DOM derived from early withered P. australis revealed a two-stage slow-fast phase, while other groups were linearly released (R2 0.87207-0.97091). A strong correlation existed between HA-like fractions and water quality index, reflecting the critical influence of plant decay in CWs operation performance. The analysis with Stern-Volmer equation indicated that plant-based DOM interacted with PAHs to form ground state complexes with possible involvement of π-π interaction, hydrogen bonding and cation bridging effect. Aromatic, molecular weight, and hydrophilicity of both DOM and PAHs affected their binding with the interaction capability in the order of BKF > Bap > PHE and C3 > C5 > C2 > C1 > C4. Besides, alkaline environment and high DO condition was highly unsuitable for the combination. Scientific management and appropriate operating condition were important in optimizing operation performance and controlling pollutant migration in CWs.

Effect of Hydroxyl Group on Photo-Physical Properties and Dipole Moments of Fluorescent Dyes: An Experimental and Computational Approach

In this work, structurally similar, (E)-N'-(2-hydroxybenzylidene)-3,5-di-tert-butyl-2-hydroxybenzohydrazide (A) and (E)-N'-(2-4-dihydroxybenzylidene)-3,5-di-tert-butyl-2-hydroxybenzohydrazide (A-OH) dyes dissolved in general solvents have been studied to explore photo-physical properties, employing solvatochromic shift method, thereby determining their dipole moments in the ground (μ_g) and excited (μ_e) states. The molecule A shows a bathochromic shift of fluorescence emission maxima in aprotic solvents whereas a hypsochromic shift in protic solvents. Interestingly, A-OH follows a hypsochromic shift in both protic and aprotic solvents with increasing solvent polarity. The effect of hydroxyl substituent on UV-Visible absorption, fluorescence emission, and dipole moment of the titled organic molecules was explained. Theoretical methods such as Bilot-Kawski method for determination of μ_g and μ_e and Bakshiev, Kawski-Chamma-Viallet, Lippert-Mataga equations for μ_e, and Reichardt method for the difference between μ_g and μ_e were employed. It is observed that μ_e is higher than that of μ_g for both the molecules, and interestingly, upon substituting an additional hydroxyl group the value of μ_g has increased while μ_e is decreased. The DFT calculations have been performed to support experimental results by employing DFT/B3LYP/6-311G + (d) and TD-DFT/B3LYP/6-311G + (d) method using Gaussian09 software. The electrophilic and nucleophilic sites on the molecules were studied with the help of MEP. The NBO analysis results show that the interaction N24 (σ) → C22-O23 (π*) is found to be stronger in both the molecules with energy 68.90 kJ/mol and the effect of hydroxyl group is also discussed on the basis of HOMO and LUMO.

Estimation of Photophysical and Electrochemical Parameters of Bioactive Thiadiazole Derivative

The absorption and fluorescence spectra of synthesized 4-[5-(2,5-Dimethyl-pyrrol-1-yl)-[1, 3, 4] thiadiazol-2-ylsulfanylmethyl]-6-methoxy-chromen-2-one (DTYMC) compound were recorded in various solvents like acetone, acetonitrile, chloroform, dimethyl formamide (DMF),1,4-dioxane, ethanol, ethyl acetate, methanol, tetrahydrofuran (THF) and dimethylsulphoxide (DMSO) at room temperature in order to estimate the ground and excited state dipole moment. The ground state dipole moment (μ_g) and excited state dipole moment (μ_e) were calculated using solvatochromic shift method which involve equations proposed by Lippert, Bakshiev and Kawski-Chamma-Viallete. The results were signified that the excited state dipole moment is greater than the ground state dipole moment, which indicates the excited state is more polar than the ground state of the molecule. The bond angle between the ground state and excited state dipole moments were found to be 0⁰, The change in dipole moment (∆μ) was calculated using microscopic solvent polarity parameter ([Formula: see text]). Further multiple linear regression analysis of Kamlet-Taft parameter, HOMO-LUMO energy were determined by cyclic voltammetry using phosphate buffer solution.