We designed a series
of photochromic derivatives by employing density
functional method (CAM-B3LYP/6-31G*). These compounds are based on
DAE (diarylethenes), both sides of which are bonded with benzene and
NiBDT (bis(ethylene-1,2-dithiolato)Ni). These substituents and, in
particular, the NiBDT moiety are known to exhibit very large second
hyperpolarizability. The objective of this work was to develop, by
employing a DFT methodology, a set of rules for designing photochromic
materials presenting the following: (i) a large contrast between a
series of physical propertiesthe hyperpolarizabilities (first
and second), the IR absorption and the two-photon absorption (TPA)
strengthof the “open” and the “closed”
isomers and (ii) extremely large nonlinear optical properties. This
large contrast may be attained by a light-induced transformation of
the “open” to the “closed” isomer, combined
with substituents involving an extensive π-electron network
and/or strong donor/acceptor pairs.