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.