Chemical Modification of CdSe Nanomaterials through Carborane Ligand Exchange

Inorganic nanocrystals capped with surfactant-like organic ligands exhibit a broad range of properties that emerge from the combination of the individual inorganic-organic components. By expanding towards functional organic ligands that are bounded on the nanocrystal surface, the charge-transport and biocompatibility of nanocrystals are enhanced, thus achieving greater chemical control of nanomaterials for targeted applications. Herein, we functionalize CdSe nanocrystals through binding with electron-donating carborane ligands (C₂B₁₀H₁₂). The synthetic preparation for CdSe quantum dots (QDs) and CdSe nanoplatelets is developed where variable concentration ligand exchange of the CdSe nanomaterials with the carborane ligands leads to changes in the photoluminescence (PL) intensity. Post-synthetic ligand exchange of the native oleate capping ligands for carborane results in a red-shift of the optical band gap of the studied CdSe QDs, while their colloidal stability is maintained based on TEM imaging. Fourier-transform infrared (FTIR) analysis demonstrates the successful incorporation of the carborane ligands onto the CdSe surfaces with the characteristic B-H resonances at 2600 cm⁻¹and 1250-600 cm⁻¹in the spectrum. Furthermore, we explore tuning the surface dipole of the CdSe core from a non-functional oleate ligand to functional carborane dipole, where the carborane dipole enables long-range ordering and higher control on the electronic properties of the resultant CdSe core/carborane shell. Altogether, this work illustrates the unique aspects of functional surface carborane ligands in controlling the optoelectronic and dipole properties of CdSe nanocrystals, which could advance their potential applications in solid-state device and bioimaging applications.