Synthesis and Stimuli‐Responsive Luminescent Properties of Phenylene‐Bridged and Non‐Bridged Boron β‐Dialdiminate Dimers

We report synthesis and optical properties of the dimers of boron β‐dialdiminate complexes with different connection manners. The series of dimers, o‐, m‐, p‐ and d‐BisDAI, were prepared, and their photophysical properties were compared with the single unit, DAI. It was found that the dimers show characteristic optical properties: o‐BisDAI showed bathochromic shifts in absorption and emission spectra and emission quenching because of the through‐space interactions, while the photophysical properties of m‐BisDAI and DAI were almost identical. The extension of π‐conjugation in p‐BisDAI could induce not only the bathochromic shifts of its absorption and emission bands but also the solvatochromism originating from the symmetry‐breaking charge transfer character. d‐BisDAI showed the weak low‐energy emission in solution and the mechanochromic luminescence which might stem from the rotational degree of freedom between the adjacent two DAI units.