Substitution effect in 2-spiropropane-1,3-diyl derivatives: A DFT and CASSCF study

Abstract

Abstract In this study, the electronic structure of 2-spiropropane-1,3-diyl and its derivatives have been investigated. Different DFT methods, including: B3LYP, BLYP, M06-2X, PBE0 and PBEPBE, have been applied to investigate the substitution effect on the geometry and stability of considered triplet diradicals. Complete active space approach has been applied to survey the effect of ground state charge multiplicity on the stability of considered diradicals. The role of through- space interactions in stabilization of singlet CH3 substituted diradical, comparing with triplet sate, has been verified. On the other hand, it has been demonstrated that, the through- bond interactions in 2-spiropropane-1,3-diyl and Cl, F, OH substituted species cause the triplet state to be more stable than singlets. The charge distributions on the studied singlet and triplet diradicals confirm the importance of the through- bond and through- space interactions, too. Different substituted diradicals have higher diradical character, comparing with the parent molecule, 2-spiropropane-1,3-diyl. Substitution of Cl group, in molecule 4, maximize the diradical character of this molecule. The NLO properties of considered diradicals have been investigated and it has been stablished that the singlet species show higher values of average second-order hyperpolarizability than triplets. The maximum NLO property is belonged to the Cl substituted 2-spiropropane-1,3-diyl singlet diradical.