Intermediate Electronic Coupling via Silane and Germane Bridges in Silicon Quantum Dot-Molecular Hybrid Systems

In hybrid Si quantum dot (QD) nanostructures, the bridge connecting the QD and molecular transmitter significantly influences photophysical transformations such as triplet exciton transfer. Here, we present two Si QD:anthracene hybrid systems with molecular silane or germane bridges that, for the first time, enable access to an intermediate QD-anthracene coupling regime. We first describe a new surface functionalization approach that uses methyl radical-mediated dehydrocoupling to install aryldialkylsilanes and germanes onto hydride-terminated Si QD surfaces. Transient absorption spectroscopy and density functional theory calculations show these tetrel bridges mediate QD-anthracene coupling strengths that are intermediate between π-conjugated vinyl and nonconjugated ethyl bridges. We optimize the new hybrids in a triplet upconversion system with 9,10-diphenylanthracene emitters and achieve photon upconversion efficiencies of 6.2% and 5.1% for silane and germane systems, respectively. This work shows that main group element bridges can provide access to QD-transmitter coupling characteristics that are distinct from conventional organic bridges.