Theoretical Investigations On The Structures And Electronic Spectra Of Several Kinds Of Heterocyclic Compounds

The ground states geometries of α-Oligothiophenes H（C₄H₂S）_nH （n=2-13） have beenoptimized by B3LYP and CAM-B3LYP methods with6-31G（d） basis set. Studies haveshown that there are three kinds of configurations: risen in a spiral, circular structure andbanded structure with curvulate. The first two present cis structures with C₁and C₂symmetries, respectively, while the last is the trans structure with C1symmetry. Thecorresponding absorption spectra have been investigated by the TD-B3LYP method and theanalytic expression of the vertical transition energies versus the size n for α-Oligothiophenesystems has been derived from the predicted ΔE-values. The emission spectra calculated atthe TD-CAM-B3LYP approach agree very well with the available experimental values.The ground states geometries of several silole and thiophene derivatives have beenexplored at the B3LYP/6-311g（d,p） level. On the basis of these configurations, we simulatedtheir UV absorption spectra at the TD-B3LYP/6-311g（d,p） level, and the studies indicate thatthe corresponding theoretical values are in good accordance with the existing experimentaldata. It is hope that our calculations will be helpful to provide a certain assistance for thefurther experiment and theoretical study.The spectroscopic properties of8-hydroxyquinoline derivatives are theoreticallyinvestigated by density functional theory （DFT） and time-dependent density functional theory（TD-DFT）. The geometries of ground states for the target molecules（E）-2-（2-（3,5-dimethyl-1-phenyl-1H-pyrazol-4-yl）vinyl）quinolin-8-ol （A） and（E）-2-（2-（1-（4-chlorophenyl）-3,5-dimethyl-1H-pyrazol-4-yl）vinyl）quinolin-8-ol （B）, as wellas potential reaction products of them with acetic acid (A_R1, A_R2, B_R1and B_R2), are optimizedby B3LYP and M06methods. The results indicate that product molecules tend to be effectively planar as compared with reactants. Subsequently, UV absorption spectra aresimulated through TD-DFT method with PCM model to further confirm the reasonableproducts of two reactions. Through the theoretical calculation, A_R2and B_R2are identified asthe target molecules. It is worth noting that the maximum absorption wavelengths ofcompounds A_R2and B_R2present prominent red shift as compared with the initial reactants Aand B, respectively, which should be ascribed to the enhancive planarity of products and thedecreased HOMO-LUMO energy gap.The geometries of ground states for two double pyrazole ring compounds（Z）-4-（（3,5-dimethyl-1-phenyl-1H-pyrazol-4-yl）methylene）-3-methyl-1-p-tolyl-1H-pyr-azol-5（4H）-one （A） and（Z）-4-（（3,5-dimethyl-1-p-tolyl-1H-pyrazol-4-yl）methylene）-3-methyl-1-phenyl-1H-pyr-azol-5（4H）-one （B）, along with the corresponding potential reaction products of them with aceticacid (A_R1, A_R2, A_R3, B_R1, B_R2and B_R3) are optimized at the B3LYP/6-31G（d） level, and thentheir stability are discussed. The vertical excited energies for the two groups of compoundsare calculated by TD-B3LYP and TD-M06methods. The results show that the vertical excitedenergies of A and B agree well with experimental data. Theoretical calculation reveals that Aand B do not react with acetic acid.