Selective heterometal doping in isostructural clusters converts phosphorescence to TADF with over 100-fold enhancing

Precise heterometal doping or substitution of specific metal sites in isostructural metal clusters remains a formidable synthetic challenge, despite its transformative potential for modulating excited-state characteristics and customizing optical properties. In this work, we achieved the precise synthesis of isostructural alloy clusters R/S-Ag3Cu ([Ag3Cu(tppm)(R/S-IPTT)]ClO4, R/S-IPTT = R/S-4-isopropylthiazolidine-2-thiolate, tppm = tris(diphenylphosphino)methane) in high yield (89%–91%) through selective doping of a Cu(I) atom into chiral homometallic cluster enantiomers R/S-Ag4 ([Ag4(tppm)(R/S-IPTT)]ClO4). In stark contrast to R/S-Ag4 (Φem R/S-Ag3Cu (Φem ≈ 70%) demonstrates strong CPL properties featured with thermally activated delay fluorescence (TADF) at ambient temperature. The selective substitution of the apical Ag(I) atom in Ag4 triangular pyramid with a Cu(I) atom not only gives rise to beyond 100-fold boosting of photoluminescence quantum yield (PLQY), but also leads to more pronounced optically chiral activity of alloy clusters in excited states in view of the larger photoluminescence dissymmetry factors (gPL) of R/S-Ag3Cu (−3.5 × 10−3/3.4 × 10−3) than that of R/S-Ag4 (−2.7 × 10−3/2.6 × 10−3). Furthermore, compared with chiral homometallic clusters R/S-Cu4 ([Cu4(tppm)(R/S-IPTT)]ClO4) with the same TADF characteristic at ambient temperature, R/S-Ag3Cu manifests 1.7-fold PLQY and 6-fold gPL due to faster reverse intersystem crossing (RISC) and more effective coupling of electric and magnetic transition moments in alloy clusters. This work not only presents a typical example of selective heterometal doping to modulate excited-state properties of isostructural metal clusters, but also gets deeper insight into the doping chemistry of dissimilar metals at the molecular level.