The singlet-triplet energy gap in divalent three, five and seven-membered cyclic C2H2M, C4H4M and C6H6M (M = C, Si, Ge, Sn AND Pb)

Total energy gaps, ΔEt–s, enthalpy gaps, ΔHt–s, and Gibbs free energy gaps, ΔGt–s, between singlet (s) and triplet (t) states were calculated for three, five and seven-membered cyclic C2H2M, C4H4M and C6H6M (M = C, Si, Ge, Sn and Pb) at B3LYP/6-311++G**. The singlet-triplet free energy gaps, ΔGt–s, for C2H2M (M = C, Si, Ge, Sn and Pb) are found to be increased in the order: C2H2Si > C2H2C > C2H2Ge > C2H2Sn > C2H2Pb. The ΔGt–s of C4H4M are found to be increased in the order: C4H4Pb > C4H4Sn > C4H4Ge > C4H4Si > C4H4C. Also, the ΔGt-s of C6H6M are determined in the order: C6H6Pb > C6H6Ge ≥ C6H6Sn > C6H6Si > C6H6C. The most stable conformers of C2H2M, C4H4M and C6H6M are proposed for both the singlet and triplet states. Nuclear independent chemical shifts (NICS) calculations were carried out for determination of aromatic character. The geometrical parameters are calculated and discussed

ELECTRONIC EFFECTS AT α-POSITION OF DIVALENT FIVE-MEMBERED RING CARBENES: SINGLET-TRIPLET ENERGIES THROUGH DFT CALCULATIONS

Thermal energy gaps, ΔEs–t; enthalpy gaps, ΔHs–t; Gibbs free energy gaps, ΔGs–t, between singlet (s) and triplet (t) states of G–C4H3C (G = –NH2, –OH, –CH3, –F, –Cl, –Br, –H, –CF3, –NO2) were calculated at B3LYP/6-311++G** level of theory. DFT calculations indicated that electron donating substituents (G = –NH2, –OH and –CH3) at α position cause to decrease ΔGs–t and electron withdrawing substituents (G = –F, –Cl, –Br, –CF3 and –NO2) lead to increase the ΔGs–t of G-C4H3C. Nuclear independent chemical shifts (NICS) calculations were carried out to determine the aromatic character. KEY WORDS: DFT calculations, Electronic effects, Singlet-triplet energies, Carbene, Five-membered, NICS Bull. Chem. Soc. Ethiop. 2009, 23(1), 151-155

Singlet-triplet gap studies on aryl-cyclopentadienylidenes: indirect electronic effects

Energy gaps, ΔXS–t (X = E, H and G) (∆Xs-t = X(singlet)-X(triplet)) between singlet (s) and triplet (t) states of aryl substituted cyclopentadienylidenes, Ar-C4H3C, were calculated at B3LYP/6-311++G**. Electron donating substituents (G = -NH2, -OH, -CH3, -F, -Cl and -Br) at phenyl group cause to increase and electron withdrawing substituents (G = -CF3 and -NO2) lead to decrease the singlet-triplet energy gaps of Ar-C4H3C. The results of the singlet-triplet gap calculations were fully supported by HOMO-LUMO gaps. KEY WORDS: Carbene, Cyclopentadienylidenes, Singlet-triplet gap, Electronic effects  Bull. Chem. Soc. Ethiop. 2010, 24(2), 311-314

Steric effect studies on solar energy storage of norbornadiene-quadracyclane system: DFT calculations

The aim of this research is to determine the possible solar energy storage in the norbornadiene (1) / quadricyclane (2) system, through involving steric effects on various position of carbon C1, C2 or C7 for 1 and 2; calculating the corresponding energies at B3LYP/6-311G** level of theory. The extent of the solar energy storage is the least for 11-i-Pr (-21.018), 12-t-Bu (-22.525) and 17-i-Pr (-17.753) when the bulk substituents (X) were occured at C1, C2 and C7, respectively

Synthesis and optoelectronic properties of hexa-peri -hexabenzoborazinocoronene

The first rational synthesis of a BN-doped coronene derivative in which the central benzene ring has been replaced by a borazine core is described. This includes six C−C ring-closure steps that, through intramolecular Friedel–Crafts-type reactions, allow the stepwise planarization of the hexaarylborazine precursor. UV/Vis absorption, emission, and electrochemical investigations show that the introduction of the central BN core induces a dramatic widening of the HOMO–LUMO gap and an enhancement of the blue-shifted emissive properties with respect to its all-carbon congener

A DFT studies on a potential anode compound for Li-ion batteries: Hexa-cata-hexabenzocoronene nanographen

In this work, the possible apply of a hexa-cata-hexabenzocoronene HCor as anode material was studied for Li-ion batteries (LIBs) using the B3LYP/6-31G* level. The planar structure of HCor is less stable (by about 0.243 hartree) in comparison with the twisted structure. The Li cation and neutral are suitably adsorbed high up the middle of a HCor hexagonal ring with the adsorption energy of -120.3 and -2.7 kcal/mol, respectively. The calculated specific storage capacity of HCor is 450.1 mAh/g and the great cell voltage is 2.63 V generated by the interaction between Li+ and HCor. The HCOR is considered an ideal candidate to be used as an anode material in LIBs because of high storage capacity and ion mobility

<b>DFT calculations on 1,4-dithiine and S-oxygenated derivatives</b>

The molecular structures of 1,4-dithiine and S-oxygenated derivatives are studied using B3LYP/6-311++G** level of theory. These compounds have 8π-electrons in the ring. This led to stabilization of non-planar conformation. DFT calculations show that 1,4-dithiine, C₄H₄SS, 1,4-dithiine-1-oxide, C₄H₄SOS, 1,4-dithiine-1,4-dioxide, C₄H₄SOSO and 1,4-dithiine-1,1,4-trioxide, C₄H₄SO₂SO; have boat conformation. 1,4-dithiine-1,1-dioxide, C₄H₄SO₂S, have a shadow boat conformation. 1,4-dithiine-1,1,4,4-tetraoxide, C₄H₄SO₂SO₂, have a planar conformation