ABSTRACTPHOTOINDUCED ELECTRON DONOR/ACCEPTOR PROCESSES IN COLLOIDAL II-VISEMICONDUCTOR QUANTUM DOTS AND NITROXIDE FREE RADICALSBYPoulami DuttaElectron transfer (ET) processes are one of the most researched topics for applications rangingfrom energy conversion to catalysis. An exciting variation is utilizing colloidal semiconductornanostructures to explore such processes. Semiconductor quantum dots (QDs) are emerging as anovel class of light harvesting, emitting and charge-separation materials for applications such assolar energy conversion. Detailed knowledge of the quantitative dissociation of the photogenerated excitons and the interfacial charge- (electron/hole) transfer is essential for optimizationof the overall efficiency of many such applications. Organic free radicals are the attractivecounterparts for studying ET to/from QDs because these undergo single-electron transfer steps inreversible fashion. Nitroxides are an exciting class of stable organic free radicals, which haverecently been demonstrated to be efficient as redox mediators in dye-sensitized solar cells, makingthem even more interesting for the aforementioned studies. This dissertation investigates theinteraction between nitroxide free radicals TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl),4-amino-TEMPO (4-amino- 2,2,6,6-tetramethylpiperidine-1-oxyl) and II-VI semiconductor(CdSe and CdTe) QDs. The nature of interaction in these hybrids has been examined throughground-state UV-Vis absorbance, steady state and time-resolved photoluminescence (PL)spectroscopy, transient absorbance, upconversion photoluminescence spectroscopy and electronparamagnetic resonance (EPR). The detailed analysis of the PL quenching indicates that theintrinsic charge transfer is ultrafast however, the overall quenching is still limited by the lowerbinding capacities and slower diffusion related kinetics. Careful analysis of the time resolved PLdecay kinetics reveal that the decay rate constants are distributed and that the trap states areinvolved in the overall quenching process. The ultrafast hole transfer from CdSe QDs to 4-AminoTEMPO observed here makes this dyad a highly promising candidate for application in quantumdot sensitized solar cells.
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