New anisopleural spindle-like nonlinear optic (NLO) chromophores with a D–D′–π–A′–A or D–A′–π–D′–A structure: interesting optical behavior and DFT calculation results

Abstract

A new series of anisopleural spindle-like chromophores which have both auxiliary donors and acceptors on their conjugated bridge has been designed and synthesized for the first time. The auxiliary donors and acceptors were introduced close to the donors and acceptors respectively and formed D–D′–π–A′–A structure chromophores termed S-chromophores. The opposite D–A′–π–D′–A structure chromophores are termed F-chromophores. The structure–properties relationship based on these anisopleural spindle-like chromophores has been investigated via¹H-NMR, UV-vis characterization and DFT theoretical calculations. S-Chromophores displayed varied chemical shifts of the double-bond proton and a red-shifted maximum absorption wavelength (λ_max) as well as a larger absorption intensity (ε) compared to the F-chromophores, indicating that the intermolecular charge transfer has been influenced by the structures. Moreover, the red-shifted λ_max and larger ε indicate a more efficient intermolecular charge transfer which should in turn lead to an increased hyperpolarizability (β) for a given class structure of chromophores. The theoretical calculation β values of the S-chromophores showing an increase further rationalize the experimental results. In this way, the structure–properties relationship has been investigated and established.