Synthesis, Spectroscopic Characterization and DFT/TD-DFT Calculations of new Fluorescent Derivatives of Imidazo[4',5':3,4]Benzo[c]Isoxazole.

An increasingly wide variety of fluorescent compounds is used in biotechnology, genomics, immunoassays, array technologies, imaging, and drug discovery. Therefore, synthesis of fluorophores with novel structural features can be interesting and useful in various fields. In this paper, four new fluorescent heterocyclic compounds with high quantum yields are introduced. These new fluorophores are synthesized in moderate to high yields via regioselective nitration of 3-alkyl-8-(4-chlorophenyl)-3 H-imidazo[4',5':3,4]benzo[c]isoxazoles. The latter compounds are obtained from the reaction of 1-alkyl-5-nitro-1 H-benzoimidazoles with (4-chlorophenyl)acetonitrile in basic MeOH solution. Physical spectral (UV-vis, IR, (1)HNMR, (13)C NMR, NOESY and fluorescence) and analytical data have established the structures of synthesized compounds. The fluorescence properties of new fluorescent heterocyclic compounds are studied. The fluorescence of all compounds is very intense and fluorescence quantum yields are high (> 0.52). Density functional theory (DFT) calculations are performed to provide the optimized geometries, relevant frontier orbitals and the prediction of (1)H NMR chemical shifts for confirming the exact structure of fluorescent compounds. Calculated electronic absorption spectra were also obtained by time-dependent density functional theory (TD-DFT) method.

Synthesis, Spectral Studies and Quantum-Chemical Investigations on the Powerful Fluorophores: Imidazo[4,5-a]acridines.

The new 3H-imidazo[4,5-a]acridine-11-carbonitriles were prepared from the reaction of 1-alkyl-5-nitro-1H-benzoimidazoles with 2-(4-methoxyphenyl)acetonitrile and benzyl cyanide by nucleophilic substitution of hydrogen in high yields. Physical spectral and analytical data have confirmed the structures of the synthesized dyes. The optical and solvatochromic properties of these compounds were investigated and the results showed that they show very interesting photophysical properties. Density functional theory (DFT) calculations of fluorescent dyes were performed to provide the optimized geometries and relevant frontier orbitals. Furthermore, intra- and intermolecular interactions in fluorescent imidazo[4,5-a]acridines were evaluated by AIM (Atoms in Molecules) analysis.