A theoretical study on the hyperpolarizabilities of dicyanovinyl and tricyanovinyl substituted benzenes, stilbenes, styrenes and azobenzenes

Calculations of conformations and hyperpolarizabilities are performed on a series of di-and tricyanovinyl substituted donor-acceptor molecules by an Finite-Field (FF) approach with AM1 Hamiltonian. Good consistency between measured and calculated hyperpolarizabilities is obtained. Based on the analysis of charges of donors and acceptors for the para-benzenes, the total amount of charge transfer from donor to acceptor and the vertical transition energy can affect the nonlinearities. Investigations on potential energy profiles for rotating of di-or tricyanovinyl acceptor or phenyl ring have shown that the changes of torsion angles between two conjugated parts of the molecular systems can alter the nonlinearities. Some molecules with large molecular hyperpolarizabilities can be designed through the optimisation for the more extended π-electron systems with proper donor and acceptor groups.