The photo-physical behavior of single CdSe quantum dots (QDs) was studied using single molecule (SM) fluorescence spectroscopy in a controlled atmosphere. Conventional SM approaches perform measurements in air, which results in rapid degradation of the QD surface and necessitate the use of some method to protect the QD surface. Most common is the use of core/shell samples. This approach has undoubtedly enabled important insights into QD photophysics during in the last 20 years, however the simplest systems--bare CdSe QDs--have been largely overlooked and are surprisingly under-investigated. Borrowing from the literature in fluorescent polymer studies, we have developed an alternate approach to protect that QD surface that enables some of the first detailed characterizations of bare QD photophysics. CdSe QDs are synthesized, SM samples are prepared, and blinking trajectories (ie, fluorescence intensity vs. time) are collected inside of a nitrogen-glovebox, all without ever exposing the samples to ambient oxygen. We find blinking kinetics are dependent on oxygen exposure. When synthesized and measured in a nitrogen-glovebox, the average power law slopes of ON-time probability distributions are mON = -1.60 ± 0.05; when measured in ambient conditions mON = -2.78 ± 0.13. Furthermore, the behavior inside the nitrogen glovebox is different than conventional core/shell samples measured in air. Probability distributions for core/shell samples measured in air exhibited a fall-off of the power law behavior around 10 s. Although the particle surface has long been understood to play a critical role in QD blinking, these results suggest blinking is much sensitive to external factors (eg, oxygen exposure) than previously recognized.

Novel approach to investigate the single molecule photophysics of bare CdSe quantum dots

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.