Asymmetric Core‐Expanded BOPYOs: Facile Synthesis and Optical Properties.

N,O‐bidentate BF2 complexes with five‐ and six‐membered core rings have been thoroughly investigated. However, the development of seven‐membered N,O‐boron complexes is still an area to be explored. We have developed BF3 ⋅ OEt2‐induced self‐condensation and coordination reactions based on a single starting material, which had been elucidated by experiment and calculation. This parent asymmetric core‐expanded borondifluoride‐(Z)‐1,3‐di(1H‐pyrrol‐2‐yl)but‐2‐en‐1‐one (BOPYO) showed reactivity with a wide range of aldehydes, thus providing a series of conjugation BOPYOs. Moreover, a BOPYO derivative with a dimethylamino group was developed as a new NIR dye that responds to acid with favorable photophysical properties based on intramolecular charge transfer effect. [ABSTRACT FROM AUTHOR]