Optically probing structure and organization : single-molecule spectroscopy on polyethylene films and a resonance Raman study of a carotenoid

Doctoral Thesis

The research in this thesis comprises two separate topics: single-molecule spectroscopy and resonant Raman spectroscopy. The first part concerns single-molecule (SM) spectroscopy on polyethylene (PE) films. Ultra thin (200 nm) films of pure high density PE were produced by spincoating. By determining the position (accuracy 10 nm) and in-plane orientation (acc. 5 deg.) of single 2.3,8.9-dibenzanthanthrene (DBATT) guest molecules, by means of SM microscopy and spectroscopy respectively, we demonstrated that these thin PE films have a shish-kebab morphology, instead of the spherulitic morphology common in thicker PE films. We have also investigated the alignment process of individual quest chromophores by stretching thicker (50 um), low density PE films. Using SM spectroscopy, we have shown that individual guest chromophores are not better aligned along the stretch direction, as draw ratio increases. Instead alignment occurs suddenly, due to the destruction and (oriented) reformation...Show moreThe research in this thesis comprises two separate topics: single-molecule spectroscopy and resonant Raman spectroscopy. The first part concerns single-molecule (SM) spectroscopy on polyethylene (PE) films. Ultra thin (200 nm) films of pure high density PE were produced by spincoating. By determining the position (accuracy 10 nm) and in-plane orientation (acc. 5 deg.) of single 2.3,8.9-dibenzanthanthrene (DBATT) guest molecules, by means of SM microscopy and spectroscopy respectively, we demonstrated that these thin PE films have a shish-kebab morphology, instead of the spherulitic morphology common in thicker PE films. We have also investigated the alignment process of individual quest chromophores by stretching thicker (50 um), low density PE films. Using SM spectroscopy, we have shown that individual guest chromophores are not better aligned along the stretch direction, as draw ratio increases. Instead alignment occurs suddenly, due to the destruction and (oriented) reformation of local crystalline regions and subsequent adsorption of chromophores. Each chromophore's orientation is determined by specific interactions with the oriented PE crystal surface. The second part of this thesis concerns a quantum-chemical analysis of the resonant Raman spectrum of the carotenoid spheroidene reconstituted in the photosynthetic reaction center (RC) of Rhodobacter sphaeroides. Our analysis demonstrates that spheroidene can adopt at least two cis forms in the RC. One of these has been conclusively shown to be the 15,15'-cis structure.Show less

Carotenoids

DBATT

Polyethylene

Resonant Raman spectroscopy

Single-molecule spectroscopy

Spincoating

Thin films