Seasonal and body size-dependent variability in the bioaccumulation of PAHs and their alkyl homologues in pearl oysters in the central Arabian Gulf.

Spatiotemporal concentration patterns for 19 parents and their alkyl homologues were measured in Pinctada radiata from 7 locations in the central Arabian Gulf around Qatar in the winter, spring and summer (2014-2015). The concentrations of PAHs ranged from 20 to 2240 (262 ± 38.0 ng·g dw) with the highest occurrence in the Doha harbor (738.

The electronic origin of the ground state spectral features and excited state deactivation in cycloalkanones: the role of intermolecular H-bonding in neat and binary mixtures of solvents.

In this study, a D-A cycloalkanone (K1) has been investigated by steady state absorption and fluorescence in neat solvents and in three binary mixtures of nonpolar aprotic/polar protic, polar aprotic/polar protic, and polar protic/polar protic solvents. The experimental findings were complemented by density functional theory (DFT), time-dependent density functional theory (TD-DFT), and NBO quantum-mechanical calculations. Experimentally, effective changes in absorption and fluorescence were observed by solute-solvent interaction.

Role of Solvent Polarity and Hydrogen-Bonding on Excited-State Fluorescence of 3-[(E)-{4-[Dimethylamino]benzylidene}amino]-2-naphthoic Acid (DMAMN): Isomerization vs Rotomerization.

The present experimental and theoretical study on a new chromophore DMAMN of the type push-π-pull (push = dimethylaniline, π = imine, pull = 2-naphthoic acid), allows understanding of the mechanism by which the molecular conformational undergoes isomerization/rotomerization following electronic excitation. The steady-state fluorescence spectra of this compound, carried out in solvents of different polarities and proticities, showed significant changes in both the shape and peak positions. The wavelength and intensity change depend on the polarity and hydrogen-bonding environment.

Intramolecular versus intermolecular hydrogen bonds in a novel conjugated dimethylamino-benzylidene-amino-2-naphthoic acid Schiff base.

A new compound based on the D-π-A concept, where D = dimethylamino-phenyl and A = naphthoic acid, separated by an imine motif, was designed, synthesized and characterized. The spectral, energetics, and structural characteristics of the compound were studied thoroughly theoretically by density functional theory (DFT) in the gas and aqueous phases and experimentally (steady-state absorption) in aqueous media with various degrees of polarity and hydrogen bonding ability. This compound shows high sensitivity to the polarity, basicity and proton affinity of the environment.

Effects of Structure and Environment on the Spectroscopic Properties of (3-Amino-Substituted-Thieno[2,3-b] Pyridine-2-yl)Pyridine/Quinolin-2-yl)(Phenyl)Methanones: Experimental and Theoretical Study.

The electronic absorption, excitation and fluorescence properties of two 3-amino-substituted-thieno[2,3-b]pyridine/quinolin-2-yl)(phenyl)methanones; (referred to as compounds 1-2: where 3-amino-4,5,6-trimethyl-thieno[2,3-b]pyridin-2-yl)(phenyl)methanone (1); and 3-amino-5,6,7,8-tetrahydro-thieno[2,3-b]quinolin-2-yl)(phenyl)methanone (2)) have been investigated in solvents of various polarity and hydrogen-bonding abilities. Results based on the electronic absorption, excitation and emission study of these compounds; indicated that singlets (S1 and S2) excited-states are populated in non-polar and polar protic/aprotic solvents giving dual fluorescence with weak charge transfer separation. The experimental results were interpreted with the aid of quantum chemistry calculations carried out with the DFT and TD-DFT/B3lyp/6-31 + G(d,p) methods.