Relationship between optical nonlinearities of H-shaped chromophores and electronegativities of their substituent groups

The novel H-shaped chromophores containing two D–π–A units locked parallel to each other are very effective chromophores, because they exhibit much higher first hyperpolarizability (β) values than the corresponding mono-D–π–A unit reference compounds and good optical transparency at 532 nm. The first molecular hyperpolarizabilities (β) of these H-shaped chromophores were determined via HRS method. In investigating relation between NLO properties and substituent groups on benzene rings, it is found that the β values of H-shaped chromophores vary directly with the difference between the Hammett constants (σ) of the electron withdrawing and electron pushing groups in the D–π–A units.