β-Position Electronic Effects on the Singlet–Triplet Gaps of Divalent Five-Membered Rings XC₄H₃M (M˭C, Si, and Ge)

Abstract

Full geometry optimizations were carried out on the singlet and triplet states of β-substituted divalent five-membered rings XC₄H₃M (X˭ ‒NH₂, ‒OH, ‒CH₃ ‒H, ‒CH₃, ‒Br, ‒Cl, ‒F, ‒CF₃, and ‒NO₂; M˭C, Si, and Ge) by the B3LYP method by using 6-311++G** basis set. The thermal energy gaps, ΔE_t–s; enthalpy gaps, ΔH_t–s; and Gibbs free energy gaps, ΔG_t–s, between the singlet (s) and triplet (t) states of the above structures were calculated by using the GAUSSIAN 03 program. The ΔG_t–s of XC₄H₃C was changed in the order: X˭ ‒Cl > ‒Br > ‒CH₃ > ‒H > ‒CF₃ > ‒F > ‒NO₂ > ‒OH > ‒NH₂. The changes of ΔG_t–s for XC₄H₃Si and XC₄H₃Ge were in the order: X˭ ‒NH₂ > OH > F > Cl > Br > CH₃ > H > CF₃ > NO₂. The geometrical parameters, including bond lengths (R), bond angles (A), dihedral angles (D), natural bonding orbital (NBO) charge at atoms, HOMO and LUMO, and dipole moments, were presented and discussed.

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GRAPHICAL ABSTRACT

Keywords:

• β-position
• DFT
• divalent five-membered ring
• electronic effects
• singlet–triplet energy gap

Acknowledgements

Payame Noor University (PNU) is gratefully acknowledged for its financial support of this research.