Highly efficient unbridged D-A+(D) chromophores based on the quinolizinium cation for nonlinear optical (NLO) applications

Novel charged D-A+ chromophores based on quinolizinium cations as acceptor unit have been prepared by treating haloquinolizinium salts with N-heteroarylstannanes under Stille reaction conditions. This approach provides an easy access to potential one-dimensional D-A+ and two-dimensional D-A+-D chromophores in which the acceptor moiety (A+) is the simple azonia cation and the donors are different π-rich N-heterocycles. The first hyperpolarizabilities (β) were measured by hyper-Rayleigh scattering experiments and the experimental data confirmed that the inherent polarization between donor and acceptor fragments modulates the NLO properties. The electronic structures and properties (including both the linear and nonlinear optical properties) of the quinolizinium chromophores were examined by theoretical (DFT, HF and MP2) calculations. A promising strategy for the rational design of D-A building blocks to create new organic-based NLO materials is proposed. Quinolozinium cation as a new efficient acceptor unit in D-A+ and D-A+-D unbridged chromophores with different π-excessive N-heterocycles is proposed. Experimental and theoretical data confirm that inherent polarization between donor and acceptor fragments modulates NLO properties. [Display omitted] •Quinolizinium cation is efficient acceptor unit in new D-A+ and D-A+(D) unbridged chromophores.•Inherent polarization between donor and acceptor fragments modulates NLO properties.•The N-protecting groups in the heterocyclic donors strongly affect the βHRS values.•Quinolizinium systems in comparison with pyridinium ones appear to perform better in terms of NLO properties.•Valuable hints for the rational design of D-A building blocks with potential application in NLO devices.