Nuclear Magnetic Resonance Spectroscopy Demonstrating Dynamic Stabilization of CdSe Quantum Dots by Alkylamines

The exchange kinetics of octylamine between a free state and a state bound to the surface of CdSe quantum dots is analyzed using nuclear magnetic resonance (NMR) spectroscopy in solution. On the basis of 1D H-1 and DOSY and NOESY spectroscopy, we find that all octylamine molecules present interact with the CdSe quantum dot surface, although the octylamine resonances and diffusion coefficient resemble those of free octylamine. This indicates that these NMR observables are a weighted average of a free and a bound state, implying that the overall octylamine exchange rate is fast as compared to the intrinsic NMR time scale. A lower limit on the first-order desorption rate constant of 50 s(-1) follows from DOSY measurements as a function of the diffusion delay. This result is compared with literature data based on the quenching of the CdSe photoluminescence upon alkylamine desorption.