The O‐doped aromatic polycycle peri‐xanthenoxanthene (PXX) was prepared from 1,1′‐bi(2‐naphthol) by means of an oxidative ring closure reaction. In solution, PXX is strongly emissive and displays well‐structured absorption and fluorescence spectra but low‐temperature phosphorescence is not detected. There is little change in geometry on excitation but, in most solvents, nonradiative decay of the excited singlet state is promoted by slight twisting of the molecular backbone. This route is partially blocked in viscous solvents and at low temperature. In the liquid phase under low friction, the rate of nonradiative decay correlates with the inverse viscosity of the solvent. Nonradiative deactivation of the excited singlet state is activated in solution while the Huang–Rhys factor is sensitive to temperature changes in a glassy matrix. Assuming the twisting movement is equivalent to translational motion about the ether linkages, Kramers’ theory allows estimation of the potential curvature at the apex of the barrier.
Erythrosine, a popular food dye, undergoes fast O-sensitive bleaching in water when subjected to visible light illumination. In dilute solution, erythrosine undergoes photobleaching via first-order kinetics, where the rate of bleaching depends critically on the rate of photon absorption and on the concentration of dissolved oxygen. Kinetic studies indicate that this inherent bleaching is augmented by self-catalysis at higher concentrations of erythrosine and on long exposure times. Under the conditions used, bleaching occurs by way of geminate attack of singlet molecular oxygen on the chromophore. Despite the complexity of the overall photobleaching process, the rate constants associated with both inherent and self-catalytic bleaching reactions follow Arrhenius-type behavior, allowing the activation parameters to be resolved. Bleaching remains reasonably efficient in the solid state, especially if the sample is damp, and provides a convenient means by which to construct a simple chemical actinometer.
A compact donor-acceptor molecular dyad has been synthesized by attaching an N,N-dimethylamino fragment to a naphthalic anhydride residue. The dyad shows fluorescence from an intramolecular charge-transfer state (i.e., charge-recombination fluorescence) in solution, with the photo-physical properties being strongly dependent on the solvent polarity. Similar emission is seen for single crystals of the target compound, the molecules being aligned head-to-head, although time-resolved emission profiles display dual-exponential kinetics. A second polymorph with the head-to-tail alignment also gives rise to two lifetimes that differ somewhat from those of the first structure, which are assigned to bulk and surface-bound molecules. Growing the crystal in the presence of Rhodamine B localizes the dye around the surface. Excitation of the crystal is followed by sub-ps exciton migration along the aligned stacks, with occasional crossing to adjacent stacks and trapping at the surface. Rhodamine B present at very low levels acts as the acceptor for excitons entering the surface layer. Crystals embedded in a polyester resin form an artificial light-harvesting antenna able to sensitize an amorphous silicon solar cell.
In this paper, the compound of (4-bromo-3-nitro-1,8 -naphthalic anhydride) and the dopant material (4-hydroxy-m-benzenedisulfonic acid) were synthesized. The UV-Vis absorption and emission spectra of the compound were recorded. 4-bromo-1,8-naphthalic anhydride was used as a starting material to prepare the compound (4-bromo-3-nitro-1,8 -naphthalic anhydride) in the presence of concentrated sulphuric acid and sodium nitrate. The dopant material (4-hydroxy-m-benzenedisulfonic acid) was prepared by using phenol in concentrated sulfuric acid. The absorption bands depend on the solvent polarity, which the compound shows significant red shift in DMSO solvent compared to in ethanol solvent.The fluorescence spectra of this compound were sensitive to the solvent polarity, the calculated result indicates that the maximum peak is shifted to red in polar solvent, to the excited states of the polar ICT, which leads to decrease the energy of the excited states. The effect of the dopant material on the conductivities (ionic and specific) of the compound was studied, the ionic conductance was increased as the weight of the dopant material increases.
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