Core-dependent properties of copper nanoclusters: valence-pure nanoclusters as NIR TADF emitters and mixed-valence ones as semiconductors

We report herein that copper alkynyl nanoclusters show metal-core dependent properties via a charge-transfer mechanism, which enables new understanding of their structure-property relationship. Initially, nanoclusters 1 and 2 bearing respective Cu( i ) 15 ( C1 ) and Cu( i ) 28 ( C2 ) cores were prepared and revealed to display near-infrared (NIR) photoluminescence mainly from the mixed alkynyl → Cu( i ) ligand-to-metal charge transfer (LMCT) and cluster-centered transition, and they further exhibit thermally activated delayed fluorescence (TADF). Subsequently, a vanadate-induced oxidative approach to in situ generate a nucleating Cu( ii ) cation led to assembly of 3 and 4 featuring respective [Cu( ii )O 6 ]@Cu( i ) 47 ( C3 ) and {[Cu( ii )O 4 ]·[VO 4 ] 2 }@Cu( i ) 46 ( C4 ) cores. While interstitial occupancy of Cu( ii ) triggers inter-valence charge-transfer (IVCT) from Cu( i ) to Cu( ii ) to quench the photoluminescence of 3 and 4 , such a process facilitates charge mobility to render them semiconductive. Overall, metal-core modification results in an interplay between charge-transfer processes to switch TADF to semiconductivity, which underpins an unusual structure-property correlation for designed synthesis of metal nanoclusters with unique properties and functions. While valence-pure copper alkynyl nanoclusters show near-infrared TADF, the mixed-valence ones exhibit semiconductivity.