Carboxylate-terminated cadmium selenide nanocrystals were chlorinated upon reaction with chlorotrimethylsilane (Me3Si-Cl) and tri-n-butylphosphine (Bu3P), producing trimethylsilyl-carboxylate esters and chloride-terminated CdSe nanocrystals with Bu3P and tri-n-butylphosphonium chloride ([Bu3P-H]+[Cl]-) co-ligands. 1H and 31P{1H} NMR spectra of nanocrystals isolated and purified by precipitation were assigned to the broad NMR signals for surface bound Bu3P and [Bu3P-H]+[Cl]- as well as free (Bu3P)2(CdCl2)2. Monitoring the chlorination in d6-benzene with nuclear magnetic resonance (NMR) spectroscopy indicates that Bu3P displaces cadmium carboxylate (Cd(O2CR)2) from the nanocrystals surface forming a soluble phosphine complex that reacts with Me3Si-Cl leading to (Bu3P)2(CdCl2)2. This decrease in Cd(O2CR)2 bound to the nanocrystals surface is accompanied by a decrease in the nanocrystal solubility and photoluminescence quantum yield (20% to <1%). Reaction of Me3Si-Cl with nanocrystals terminated by alkylphosphonates or contaminated with carboxylic acids, alcohols, or primary amines, causes a blue-shift of the absorption features, an increase in the photoluminescence quantum yield and leads to a variety of trialkylphosphonium-chloride- or alkylammonium-chloride-bound nanocrystals.

Trialkylphosphine complexes of chloride-terminated cadmium selenide quantum dots

244th National Meeting (2012)

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