Use of norbornadiene in solar energy storage: Theoretical study of a Copper(I) photosensitizer for the norbornadiene-quadricyclane transformation

Density functional calculations with the hybrid B3LYP functional have been used to study the ground state of norbornadiene bound to the photosensitize r [Cu(8-oxoquinolinato)]. The main bonding interaction between the ligand a nd the metal is pi back-donation, metal to ligand, which reduces the pi-pi* band gap in norbornadiene. CIS calculations performed on free norbornadien e and on the system where norbornadiene interacts with the photosensitizer have shown that the photosensitizer reduces the excitation energy to promot e the system to the first excited singlet state. In terms of wavelength, th is difference implies that light with lambda almost 100 nm longer can be us ed to photoactivate the norbornadiene with respect to free norbornadiene.