Research Projects

Over the past two decades, low-valent main-group compounds have become important alternatives to transition metals in catalysis, attracting attention due to their unique bonding, reactivity, and electronic properties. These compounds can mimic transition metal reactivity such as hydrogenation, C-H activation, and small molecule activation (e.g., N₂, CO₂). Their ability to activate inert molecules such as H₂, N₂, CO₂, and even hydrocarbons make them particularly valuable in fundamental chemistry and catalysis. Despite this promise, their use in light emission remains largely unexplored, opening an opportunity to develop a new frontier in luminescence. This proposal aims to develop efficient light-harvesting molecules using low-valent main-group compounds, specifically borylenes (B(I)), silylenes (Si(II)), and germylenes (Ge(II)) from groups 13 and 14. Borylenes (RB:) are boron +1 species known for their electron-deficient nature and high reactivities whereas silylenes (R₂Si:) and germylenes (R₂Ge:) are in the +2 state and show unique bonding patterns due to their lone electron pairs and electron deficiency. These low-valent compounds can be stabilized using NHC (N-heterocyclic carbene), CAAC (cyclic alkyl(amino) carbene), or carbone ligands. This research proposal aims to replace the R group in borylene (R-B:), silylene (R₂Si:), and germylene (R₂Ge:) with highly conjugated units, such as dimesitylborane-oligothiophenes [(Mes)₂B-(Th)n], diphenylphosphane-oligothiophenes [Ph₂P-(Th)n], and N,N-diphenylamine-oligothiophenes [Ph₂N-(Th)n], (Th = thiophene and n = 2, 3) and plans to synthesize their NHC/CAAC/Carbone-stabilized low-valent borylene, silylene, and germylene molecules to achieve efficient light absorption and emission by tuning the HOMO-LUMO energy gaps. The synthesis of (Mes)₂B-(Th)n, Ph₂P-(Th)n, and Ph₂N-(Th)n will follow literature procedures. To obtain NHC/CAAC-stabilized borylenes (R-B:), the R groups i.e. (Mes)₂B-(Th)n, Ph₂P-(Th)n, and Ph₂N-(Th)n will react with n-BuLi and be trapped with trimethylsilyl chloride. The resulting products, (Mes)₂B-(Th)n-TMS, Ph₂P-(Th)n-TMS, and Ph₂N-(Th)n-TMS, will be subjected to silicon exchange with BBr₃ to produce (Mes)₂B-(Th)n-BBr₂, Ph₂P-(Th)n-BBr₂, and Ph₂N-(Th)n-BBr₂. These intermediates will be reduced with KC8 in the presence of NHC/CAAC to yield NHC/CAAC-stabilized borylenes [R-B:←L₂; L = ligands]. To synthesize NHC/CAAC/carbone-stabilized silylenes (R₂Si:←L) and germylenes (R₂Ge:←L), (Mes)₂B-(Th)n, Ph₂P-(Th)n, and Ph₂N-(Th)n will react with n-BuLi and be quenched with NHC-SiCl₂/CAAC-SiCl₂/carbone-SiCl₂ or NHC-GeCl₂/CAAC-GeCl₂/carbone-GeCl₂. By fine-tuning the steric and electronic properties (σ-donors and π-acceptors) of the carbene ligands, this project aims to systematically explore structure-property relationships, adjusting the HOMO-LUMO gaps to yield enhanced photoluminescence and expand the applications of low-valent main-group compounds into luminescent materials and photocatalysis.