Spectroscopic Studies of CdSe Nanocrystal Fine Structure and Electronic Coherences in Cryptophyte Algae
Bibliographic record
Abstract
The studies presented in this thesis explore energy transfer and relaxation in excitonic systems using two types of third-order non-linear spectroscopy, transient grating (TG) and two-dimensional photon echo (2DPE). Two major excitonic systems are studied, colloidal CdSe nanocrystals and a photosynthetic system, the light harvesting antenna protein PE545 isolated from cryptophyte algae Rhodomonas CS24. \n\nThe inhomogeneous broadening present in colloidal samples has long been an obstacle to the study of the fine structure of CdSe nanocrystals. This thesis will present two studies, each using a different spectroscopy to overcome this problem and gain insight into the fine structure of the ground state exciton and biexciton. In both cases, polarization dependent measurements are used to isolate particular types of pathways through the fine structure. \n\nPolarization dependent TG measurements and a detailed kinetic model have allowed us to identify major pathways for excitonic relaxation within the fine structure of the ground state exciton, despite the inhomogeneous broadening present in the sample. Conclusions from this work include an analogy to the internal conversion and intersystem crossing transitions in molecules, concepts which are familiar to most chemists.\n\nPolarization dependent 2DPE experiments and a simulation of the resulting spectra have allowed for the direct observation of the ground state biexcitonic fine structure. The high density of states in the spectral region of the biexciton obscures these states in most spectroscopies, but the combination of polarization dependence and the use of a two-dimensional technique have revealed these elusive fine structure states.\n\nThis 2DPE technique is then used to inspect light harvesting antenna protein PE545, a system of eight chromophores covalently bonded to a protein scaffold. The 2DPE measurement is capable of identifying oscillatory components of the signal which are signatures of coherent energy sharing. Using this technique, coherent energy sharing is observed throughout the spectrum of the protein at ambient temperatures, and control experiments suggest that the observed coherences are electronic, not vibrational.\n\nA short study is also presented which compares the utility of two approximations for calculations of electronic coupling and energy transfer in elongated excitonic systems.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".