Date of Award
Doctor of Philosophy
Dr. Ramakrishna Guda
Dr. Sherine Obare
Dr. Ekkehard Sinn
Dr. Tianshu Liu
two-photon absorption, chromophores at interfaces, electron injection, ultra-fast dynamics, dye-sensitized solar cells, stark effects
Materials with large two-photon absorption (2PA) cross-sections found applications in several areas such as sensor protection, 3D micro/nano fabrication, photodynamic therapy, optical data-storage, multi-photon sensing, multi-photon microscopy and imaging. Several successful research strategies were developed in literature to achieve 2PA materials with enhanced cross-sections. However, the obtained cross-sections are far from adequate and there is a need to develop new strategies. In a parallel development, numerous research efforts were focused on studying the dynamics of interfacial charge-transfer (ICT) across chromophoresemiconductor interfaces, especially in the context of dye-sensitized solar cells. While investigating the fundamentals of ICT, it was found that these interfaces provide greater dipolar coupling and can create surface electric fields. Thus, the hypothesis of the present thesis is to use the local electric fields and interfacial interactions to enhance the 2PA crosssections of attached chromophores. This strategy of chromophores stationed at interfaces can lead to synergistic 2PA enhancement. To prove the hypothesis and design better 2PA materials, following research work was undertaken. Firstly, ICT dynamics on three anthracene derivatives-sensitized TiO2 nanoparticles was studied to understand the influence of anchoring groups and corroborate the presence of local electric fields. Secondly, investigations were continued to probe the dynamics of electron injection and transient Stark effects in a donor-pacceptor chromophore sensitized TiO2 nanoparticles. Thirdly, new chromophores are synthesized that can possess strong interfacial electronic coupling with the semiconductor and create local electric fields. The 2PA cross-section measurements of these chromophoressensitized semiconductor nanoparticles have shown unprecedented 2PA enhancements as high as 20-fold when the chromophores are attached to the semiconductor nanoparticles. The mechanism behind the enhancement was probed with ultrafast luminescence and absorption and the results confirmed the presence of a charge-transfer state. Finally, the interfacial electric field generated at the interface of charged micelle and water was used to enhance the 2PA cross-sections of chromophore that was solubilized in that region. The results presented in the thesis have confirmed that local electric fields exist at the interfaces and they can be successfully utilized to design efficient 2PA materials.
Bairu, Semere Ghebru, "Ultrafast Dynamics and Two-Photon Absorption Properties of Chromophores at Interfaces" (2013). Dissertations. 175.