| Reversible trans-cis photoisomerization exists widely in organic materials, and azo dye is one type of those materals. Upon absorbing a photon, azo molecules isomerize from the thermal stable trans isomer to metastable cis isomer. Based on the significant differences of two isomers in absorption spectra and nonlinear polarizability, such photo-sensitive behavior of molecular structure change gives rises to the applications in nonlinear optics, molecular photo-electric switch, optical storage and holography.The tunable surface plasmon resonance of gold nanoparticles is appled to the system of azobenzene molecules in this thesis and the control of photoisomerization quantum efficiency by different structures of gold nanoparticles is realized. This thesis focuses on following aspect:1. Through researching and summarizing, we use chemical methods to prepare gold nanoparticles of different sizes and substrate samples of different nanostructures, and characterize them with spectrometer, XRD and AFM.2. We studied the effect of gold nanoparticles on the photoisomerization of disperse red one (DR1), and quantitatively measured and analyzed the photoisomerization quantum efficiency of DR1 molecule. The photoisomerization quantum efficiency of DR1 molecule can be largely manipulated by placing the dye molecule on different gold nanostructures. With DR1 on the gold island film, the quantum efficiency of trans-to-cis isomerization is enhanced by 90%, and when DR1 is on self-assembled films or loose film of gold particles, a severe reduction of photoisomerization quantum efficiency happens and the reduction can be as large as 45% of the free dye value.3. We measured surface enhanced Raman scattering signal of DR1 molecule and fluorescence lifetime of Rhodamine B on the gold film of different nanostructures, and analyzed the enhancing and quenching effects of different gold nanostructues, which helped us understand the effect of gold nanoparticles on the photoisomerization of DR1 molecule. |
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