Comprehensive Summary
Carbolong compounds as a metal‐heteroaromatic compound with both organometallic properties and π‐conjugated systems exhibit great potential in organic catalysis and optoelectronic devices. In this work, for the first time, the “Bucket Effect” is revealed to promote the third‐order nonlinear optical (NLO) performance in metal‐heteroaromatic compounds. We have successfully constructed and investigated a series of novel metallapentalenes with higher third‐order NLO performance benefited from the “Bucket Effect”. Meanwhile, aromaticity and electron−hole analysis further confirm the internal homogeneity of organometallic rings, reduced bandgap, and enhanced low‐energy peak response resulted in the enhanced third‐order NLO effects. The success of this work is discovering an emerging material library of high third‐order NLO effects, and illustrating the feasibility of engineering the high response metal‐heteroaromatic optical devices at the electronic structure level.