Cornelis A. van Walree, Okke Franssen, Albert W. Marsman, Marinus C. Flipse and Leonardus W. Jenneskens
The second-order nonlinear optical (NLO) and electronic properties of
stilbenes (CC bridge), benzylideneanilines
(C
N and N
C bridges) and azobenzenes
(N
N bridge) containing either an
N,N-dimethylamino donor and/or a
nitro acceptor were investigated using EFISH, UV spectroscopy, cyclic
voltammetry and PPP/SCF calculations. It appeared that although first
hyperpolarizabilities of the ethylene and azo bridged
donor–acceptor compounds are of comparable magnitude, substitution
of one carbon by a nitrogen atom reduces the NLO activity. Differences
in hyperpolarizabilities were rationalized with the aid of a two-level
model, which revealed that they find their origin in the redox activity
of the nitrogen-containing bridges.