Solar energy storage in norbornadiene-quadricyclane system: electronic effects via ab initio computations

Electronic effects involved in the solar energy storage in norbornadiene (1)/quadricyclane (2) system, are investigated using ab initio methods at HF/6-31G* and DFT/6-31G* levels of theory. Substituents X, with various Hammett σ constants, are placed at the para carbon of a phenyl ring, attached to the C2 of 1 and/or 2. A Hammett ρ value of −0.81 is encountered; indicating that electron donating substituents (-NMe2, -NH2, -OMe, -OH and -Me) induce storage of higher quantities of solar energy, than electron withdrawing groups (-NO2, -F, -Cl, -Br, -CF3 and -COOH).