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The novel 7-hydroxy-3-(3,4,5-trimethoxyphenyl)coumarin ( 1 ) has been synthesized via Perkin reaction and its phthalonitrile derivatives ( 2 , 3 , 4 and 5 ) have also been prepared from the reaction of this coumarin ( 1 ) with 3-nitrophthalonitrile, 4-nitrophthalonitrile or 4,5-dichlorophthalonitrile compounds for the first time in this study. The newly synthesized compounds have been fully characterized by 1 H NMR, MALDI-TOF, FT-IR, UV–vis and fluorescence spectral data as well as elemental analysis. The exact structure of the coumarin substituted phthalonitrile derivatives ( 2 , 3 and 5 ) have also been determined using X-ray diffraction. The electronic absorption and fluorescence properties of these new compounds have been studied in different solvents. The chemosensor behaviors of these compounds to metal ions have also been examined by fluorescence spectroscopy and these compounds exhibited as fluorescence chemosensor for the determination of Fe 3+ ions in solution. Fe 3+ complex structures of mono-coumarin ring substituted derivatives ( 1–4 ) have been investigated by using density functional theory computations.

The aromaticity of 1,3,4-thiadiazole-2-thione and its oxygen analogs including their tautomeric forms, and 1,3,4-thiadiazole, 1,3,4-oxadiazole, furan, thiophene, cyclopentadiene, the cyclopentadienyl anion and the cyclopentadienyl cation has been examined by harmonic oscillator measure of aromaticity (HOMA), aromatic stabilization energy (ASE), differential heat of hydrogenation (Δ Δ HH), and nucleus independent chemical shifts (NICS (0)), calculated at the HF/6-31G**, B3LYP/6-31G**, B3LYP/6-311G**, and B3LYP/6-311++G** levels. A principal component analysis (PCA) of the data set generated from these aromaticity results has been presented and compared with similar analyses in the recent literature. It has been shown that aromaticity is at least a two-dimensional phenomenon, independent of the level of the computational method employed. We observed that the sulfur-containing heterocyclic compounds are more aromatic than their oxygen analogs according to geometrical aromaticity measurements. In addition, our calculations of the energies of the tautomeric forms showed that the carbonyl and thiocarbonyl tautomers are more stable than the hydroxy and mercapto forms, which is in good agreement with the experimental findings in the literature.