UC Riverside

Hybrid organic nanocrystal materials outstand as good candidates in photovoltaic cells, photodetectors, light emitting devices, phototherapies and optogenetics applications due to controllable bandgap via varying size and shape in synthesis and tunable optical and electronic properties via surface modification. My dissertation is mainly focusing on two parts: (a) Chemically surface modification of semiconductor nanocrystals with anthracene derivatives to serve as triplet sensitization in energy transfer process (b) Chemically surface modification lead sulfide semiconductor nanocrystals to tune band offsets and alignment of PbS QDs in thin film transistors.

Starting from anchoring anthracene carboxylic acid and anthracene dithiocarbamate acid isomers on CdSe nanocrystal surface to investigate how molecular orientation and orbital overlap affects triplet energy transfer from NC donor to anthracene transmitter on the hybrid photon upconversion system. We are interested in the effect of isomeric substitutions on the transmitter for triplet energy transfer between nanocrystal donor and molecular acceptor. Each isomeric acceptor is expected to bind in a unique orientation with respect to the NC donor. We see that this orbital overlap drastically affects the transmission of triplets and small perturbations to molecular structure can drastically realign the relative levels of excited states, thus impacting TET transfer in this hybrid platform.

Photostable nontoxic and earth abundant hybrid semiconductor nanocrystals are in demand for triplet sensitization in biological and environmentally-sensitive applications including phototherapy and bioimaging. However, hybrid nanocrystal materials applied in triplet sensitization to date have made exclusive use of NCs containing toxic elements or expensive rare earth elements. We address this challenge by chemically functionalizing non-toxic silicon NCs with triplet-accepting anthracene ligands, upconverting 488 – 640 nm photons to 425 nm violet light further for biological use.

Fully fluorinated perfluorocarbon ligands are shown to modify the energetics and dielectric environment of quantum dots resulting in a large hypsochromic shift in the optical gap. This work shows that electron-withdrawing halogens like fluorine and chlorine can control the bandgap and band offsets of nanocrystals for the future design and optimization of functional organic/inorganic hybrid nanostructures.

Motivated by the oleophobic and electron-withdrawing nature of perfluorocarbons, I explore the effect of a trifluoromethyl coating on lead sulfide quantum dots in thin film transistor geometry. The low surface energy conferred by the oleophobic perfluorocarbons creates QDs packed in a primitive cubic lattice with long range order.