Synthesis of charged bis-heteroaryl donor–acceptor (D–A+) NLO-phores coupling (π-deficient–π-excessive) heteroaromatic rings†
Charged chromophores based on heteroaromatic cations were prepared by reaction of alkylazinium salts with N-heteroarylstannanes under Stille conditions. This approach provides easy access to potential single donor D–A+ chromophores in which the acceptor moiety A+ is the pyridinium cation and the donors are different π-excessive N-heterocycles. The β hyperpolarizabilities were measured in hyper-Rayleigh scattering experiments and the experimental data are supported by a theoretical analysis that combines a variety of computational procedures, including density functional theory and correlated Hartree–Fock-based methods. In some chromophores, the absence of a bridge between donor and acceptor fragments increases the NLO properties.