UC Santa Cruz

Two-photon photoluminescence (2PPL) together with hollow gold nanosphere’s (HGN's) photothermal properties are utilized as a single theranostic agent for cancer. HGNs bioconjugated with folic acid-PEG-thiol (HGN-FA) selectively bind to the overexpressed folate receptor of cervical cancer HeLa cells and the 2PPL from HGN-FA captures high-resolution cancer cells images using multiphoton microscopy. Subsequent power increase and laser scanning dwell time results in highly efficient photothermal destruction of cancer cells. Using femtosecond laser pulses, microseconds of laser exposure generates well-localized superheating of HGNs, yielding subcellular thermal damage and cell death.

The following chapters transition to the synthesis and characterization of colloidal and solid film perovskite quantum dots (PQDs). Important hindrances for commercialization of PQD solid film in optoelectronic devices are insufficient charge transport and long-term stability. This is mostly contributed to their lack of charge transfer in PQD solid films and degradation in the presence of moisture, oxygen, heat, and light. These hindrances can be overcome by exploring different surface ligand passivation strategies and understanding their functionality associated with PQD solid film's optical, electronic, and electrical properties. Enhancing the charge transport properties of PQDs is dependent on mitigating the tunneling barrier which is imposed by the distance charges must travel between PQDs. Using long alkyl chain passivating ligands instills greater stability, however, a diminishment in charge transport. Moreover, short alkyl chain or counter ion passivation leads to instability but improved charge transport. To overcome these inversely related properties, an effective strategy to mitigate the charge tunneling barrier and simultaneously provide stability is passivating with exciton-delocalization ligands (EDLs). EDLs consist of π delocalizing orbitals that hybridize with the electronic wave function of PQDs. This enables charges to delocalize to the PQD’s surface and eliminates the tunneling barrier imposed by surface ligands. The following chapters discuss the dependence of charge transport and stability of PQD solid film on the capping ligand chain length, and then, the investigations of using EDLs for enhancing the optical and charge transport properties of PQD solid film.

The final chapter discusses the synthesis of perovskite magic sized clusters (PMSCs). Specifically, the ligand dependence of their growth and optical properties. Here, PMSCs are synthesized using an excess amount of capping ligands. The two different ligand combinations used to synthesized PMSCs are butylamine-valeric acid (BTYA-VA) and 3,3-diphenylpropylamine-valeric acid (DPPA-VA). These PMSCs were observed to have the bluest shifted absorption and PL peaks that correspond to their smallest stable size. For BTYA-VA PMSCs, the excitonic absorption peak is at 424 nm and PL peak at 434 nm, while the DPPA-VA PMSCs exhibited an absorption peak at 428 nm and PL peak at 451 nm. Due to the shift in absorption, the size of PMSCs is determined to be ligand dependent. In addition, it was discovered that different size PQDs can be synthesized from DPPA-VA PMSCs that correspond to a specific dilution. This method to precisely tune size, and hence, optical properties simply by dilution may provide a more exact and facile synthesis of PQDs.