A Library of Selenourea Precursors to PbSe Nanocrystals with Size Distributions near the Homogeneous Limit

We
report a tunable library of N,N,N′-trisubstituted selenourea precursors
and their reaction with lead oleate at 60–150 °C to form
carboxylate-terminated PbSe nanocrystals in quantitative yields. Single
exponential conversion kinetics can be tailored over 4 orders of magnitude
by adjusting the selenourea structure. The wide range of conversion
reactivity allows the extent of nucleation ([nanocrystal] = 4.6–56.7
μM) and the size following complete precursor conversion (d = 1.7–6.6 nm) to be controlled. Narrow size distributions
(σ = 0.5–2%) are obtained whose spectral line widths
are dominated (73–83%) by the intrinsic single particle spectral
broadening, as observed using spectral hole burning measurements.
The intrinsic broadening decreases with increasing size (fwhm = 320–65
meV, d = 1.6–4.4 nm) that derives from exciton
fine structure and exciton–phonon coupling rather than broadening
caused by the size distribution.