Single Molecule Study of Fluorescence from Organic Dyes at Interfaces Público

Goh, Wan-Hee (2007)

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Single molecule study has been performed on the fluorescence emitted from organic dyes adsorbed on nanocrystalline films. The basic configuration of the study was rhodamine B (RB) and PDI derivative (PDI-P1) [N-octyl-1,7(3’,5’ di-tert-butylphenoxy)perylene-3,4:4,10-bis(di-carboximide)-benzoic acid] dyes adsorbed on the surfaces of various nanocrystalline substrates at extremely low surface number density ~ 0.06 molecule/mm2: nanocrystalline Antimony doped Tin Oxide (ATO, Sb:SnO2), glass, and nanocrystalline ZrO2 film. The nanocrystalline ATO substrate accepted an electron from the excited state of the single RB or PDI-P1 dye. Electron transfer (ET) to the glass and the nanocrystalline ZrO2 is not allowed energetically. Properly sampled single RB molecules on ATO had fluorescence lifetime distribution with average 0.7 ns. Typical average of single molecule fluorescence lifetime (SMFL) distribution of RB on glass or on ZrO2 ranged from 3.0 to 3.4 ns. The significant reduction of lifetime by more than 2 ns is ascribed to the electron transfer from RB to ATO. Similarly, the average of SMFL distribution of PDI-P1 on ATO was 1.2 ns, while those on glass and on ZrO2 were 2.9 ns and 3.7 ns respectively. The lower limit of our SMFL detection was about 100 ps. Therefore, many molecules that had electron transfer channel in less than tens of picosecond time scale were not detectable due to their low quantum yields. The SMFLs of detected molecules in nanoporous film were controlled by not only the ET process but also nearby optical and dielectric environment. Local field correction and effective medium approximation theories were applied to the interpretation of the measured SMFL distributions. The glass was an ET-inactive substrate but it interacted with adsorbed dye in a peculiar way. There was a power loss through the air-glass surface depending on the orientation of emission dipole of a single molecule, which resulted in the finite lifetime distributions of RB and PDI-P1 dispersed on glass. The most probable dipole orientation of the dyes on glass was estimated to be about 65° from surface normal. The unique intensity fluctuations of RB on glass has been observed. We have accumulated new evidences and proposed a tentative conclusion that RB on glass forms multiple long lived dark states dynamically. We have occasionally seen interesting correlations between intensity trajectory and fluorescence lifetime trajectory mostly for PDI-P1 single molecules adsorbed on the substrates. The correlations were ascribed to the conformation fluctuation pivoted on the rigid surfaces.

Table of Contents

Abstract Acknowledgments List of Illustrations List of Tables Chapter 1. Overview of Single Molecule Study of Fluorescence from Organic Dyes at Interfaces Chapter 2. Theory of Fluorescence Lifetime in Single Molecule Detection I. Introduction II. Elements of Fluorescence III. Radiative Lifetime Dependence on Optical Environment III.A. Local Field Effect III.B. Orientation of Dipole on a Dielectric Flat Surface IV. Criterion of Goodness of Fit V. Conclusion References Chapter 3. Microscopy and Sample Preparation for Single Molecule Detection I. Sample Preparation I.A. Cleaning I.B. Nanoporous Film Preparation I.C. Sensitizing the Nanoporous Film with Organic Dye in Single Molecule Level II. Single Molecule Microscopy II.A. Time-Correlated Single Photon Counting II.B. Experimental Setup for Single Molecule Lifetime Measurement by TCSPC III. Single Molecule Detection Method III.A. General Procedure III.B. Proper Number Density for SM Detection III.C. Statistical Fluctuation of Virtual SMFL Source IV. Conclusion References Chapter 4. Single Molecule Detection of Rhodamine B on the Surface of Nanocrystalline Thin Film and Glass I. Introduction II. Results II.A. Bulk Fluorescence Lifetime Measurement of RB on ATO II.B. Single Molecule Detection II.B.1. Single Molecule Imaging II.B.2. Single Molecule Intensity Trajectory II.B.3. Experimental Evidences of Single Molecule Detection II.C. Single Molecule Lifetime Measurement II.C.1. SMFL of RB on ATO II.C.2. SMFL of RB on ZrO2 III. Discussion III.A. Fluorescence Lifetime of RB on ATO III.A.1 General Description III.A.2. Features of the Electron Transfer Observation in Single Molecule Level III.A.3 Origin of Radiative Lifetime Dispersion IV. Conclusion Appendix A: Polarization Dependence of Fluorescence Intensity Appendix B: Solubility of Oxygen in Water and Alcohol References Chapter 5. Surface Induced Fluorescence Lifetime Distribution of Rhodamine B on Glass Measured by Single Molecule Detection I. Introduction II. Results II.A. Bulk Fluorescence Lifetime of RB on Glass II.B. Single Molecule Fluorescence Lifetime of RB on Glass Surface III. Discussion III.A. Single Molecule Fluorescence Intensity Trajectory III.B. Single Molecule Fluorescence Lifetime IV. Conclusion References Chapter 6. Single Molecule Detection of PDI-P1 on Nanocrystalline Thin films I. Introduction II. Results II.A. Bulk Test of PDI-P1 on ATO II.B. Bulk Test of PDI-P1 on Glass II.C. Bulk Test of PDI-P1 on ZrO2 II.D. SMFL Test of PDI-P1 on ATO II.E. Single Molecule Fluorescence Lifetime of PDI-P1 on Glass II.F. SMFL of PDI-P1 on ZrO2 III. Discussion III.A. SM and Bulk Lifetimes of PDI-P1 on ATO III.B. Single Molecule and Bulk Lifetime of PDI-P1 on Glass Surface III.C. Single Molecule and Bulk Lifetime of PDI-P1 on ZrO2 IV. Conclusion References

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