Quantum-Chemical Study of Aggregation of 5-(4'-Dimethylaminobenzylidene)Barbituric Acid

Abstract

Decreasing fluorescence efficiency in the solid-state is general and is mainly attributed to the intermolecular vibronic interactions, which induce the nonradiative deactivation process. Whereas the isolated dye molecules are virtually non-luminescent in dilute solutions, they become highly emissive upon solution thickening or aggregation in poor solvents or in the solid-state show an increase of luminescence intensity, the phenomenon of the aggregation-induced emission (AIE phenomenon). The development of efficient luminescent materials is a topic of great current interest. Theoretical calculation shows that the dye molecules' aggregation-induced emission characteristics result from intermolecular interactions. Utilizing such features, the molecules can be employed as fluorescent probes for the detection of the ethanol content in aqueous solutions. Quantumchemical calculations using the method of density functional theory the computations of structure and electronic spectra of aggregated forms of 5-(4’-dimethylaminobenzylidene)barbituric acid and the Gaussian 98 program packages have been performed. The unusual spectral behavior of 5-(4’-dimethylaminobenzylidene)barbituric acid was investigated theoretically by the DFT method and its time-dependent variant TDDFT. Carried out calculations using Zindo, as well as ab initio calculations, confirm the appearance of a new band during aggregation and its shift to the red region when the number of molecules increases.