Semiconductor Nanoplatelets for Imaging and Energy Transfer
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Abstract
This work deals with the application of CdSe nanoplatelets (NPLs) for imaging and energy transfer. NPLs are semiconductor nanocrystals which experience 1D quantum confinement due to their geometry, thus behaving as colloidal quantum wells. The 1D quantum confinement enables new possibilities relative to the well-studied 3D confined quantum dot counterpart. In the framework of imaging and energy transfer, this includes the possibility of overcoming the problem of inhomogeneous broadening, arising from colloidal synthesis of nanocrystals and the possibility of increasing the absorption cross section of the particle without changing its band gap i.e. its spectral properties. To utilize the excited state of NPLs to do useful work is a matter of controlling how they are quenched. In essence, this is done by controlling the distance between the NPL and their potential quenchers. In this work, triplet energy transfer was achieved by close attachment of 9-anthracene carboxylic acid ligands on NPLs to allow Dexter-like energy transfer. Förster Resonance Energy Transfer was achieved through similar means by using an organic fluorophore, which absorbs in the region of the NPLs’ photoluminescence. The photoexcited NPLs were also used to catalyze the transformation of nitrobenzene to azoxybenzene, without overreduction to aniline. When fluorescence is desired for application in imaging, the quenchers are put aside by introducing a shell of CdZnS and organic polymer, isolating the surface of the NPL electronically and chemically. This work also shows the benefit of the polymer coating, allowing the NPLs to be colloidally stable in biological medium and withstanding the conditions for encapsulation, allowing them to be used as imaging markers to visualize nanocarriers. In short, this work demonstrates the viability of NPLs for imaging and energy transfer applications and revealed key parameters relevant to develop the NPLs better for such applications.