Emissive BN-Embedded Cumulenes: Synthesis and Bidirectional Photocurrent Modulation

Embedding boron and nitrogen (BN) units into π-conjugated frameworks provides an effective strategy to tune electronic structures by introducing intrinsic orbital polarization arising from the vacant p orbital of boron and the lone pair of nitrogen. While BN-embedding has been extensively explored in C(sp²) polyaromatic hydrocarbons (PAHs), its impact on the optoelectronic properties of C(sp)-rich systems remains underexplored. Here we report air- and moisture-stable BN-capped sp-carbon chains that are isoelectronic to [3]- and [5]cumulenes ([n]BN, n = 3, 5). Structural and spectroscopic analyses reveal that BN-embedding induces pronounced polarization and localizes the high-frequency skeletal vibrations. Consequently, [n]BN exhibit excimer-like solid-state fluorescence, whereas the all-carbon counterparts remain weakly or non-emissive. Leveraging the characteristics of excited-state charge separation and asymmetric carrier injection, heterojunction optoelectronic devices incorporating [3]BN display unique bidirectional photocurrent modulation, establishing BN-embedding as an effective strategy to tune the electronic structure and emergent functions of C(sp)-rich systems.