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(sp 2 ) 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.