京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第20728号 / エネ博第356号 / 新制||エネ||70(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 坂口 浩司, 教授 萩原 理加, 教授 佐川 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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Molecules that are non-superimposable on their mirror image are named chiral or optically active compound. Over the years, molecular chirality has played an essential role in the understanding of fundamental aspects associated the origin of life, drug and food technologies and, asymmetric catalysis, among others. Moreover, most of the groundbreaking discoveries and advances made in this field have happened due to the development of spectroscopic techniques based on the natural asymmetry of the enantiomers and their ability to preferentially absorb right or left polarized light. For instance, circular dichroism (CD), which measures the difference in absorption between these two states of polarized light, has emerged as one of the most useful spectroscopic methods to identify and characterize chiral compounds. Unfortunately, CD is based on linear absorption which, in most common organic molecules, takes place in the UV region of the spectrum where the majority of organic solvents absorb as well. This certainly imposes limitations in the indiscriminated applicability of this technique to the study of chiral chromophores of biological interest in non-aqueous solutions. Consequently, a systematic and comprehensive characterization of the electronic and optical properties of such molecular entities still remains a major issue to be addressed. On this regard, nonlinear optics offers new alternatives to overcome some of the shortcomings of the standard linear CD-based spectroscopy. In order to surmount the existent limitations in this field and deepen in the fundamental understanding of chiral systems, we have mainly directed the attention of our research to the experimental and theoretical study of the polarization dependent two-photon absorption (2PA) of several chiral azo-compounds and binaphthol derivatives in solution. The first part of this dissertation (Chapters I-IV) covers a full characterization of the linear and nonlinear optical properties of a series of non-chiral and chiral azo derivatives. The combination of experimental techniques such as absorption, fluorescence, excitation anisotropy, circular dichroism, two-photon absorption and two-photon absorption circular-linear dichroism in combination with density functional theory calculations allowed us to unambiguously distinguish and assign the spectral position of the main electronic transitions (n-[pi]* and [pi]-[pi]*) in azobenzene derivatives. Our results represent a major contribution to the understanding of the electronic structure of these organic chromophores which have been reported of potential interest in the design of optoelectronic devices. Then, Chapter V describes the development of a novel experimental technique called the synchronized double L-scan for the study of polarization dependent multiphoton absorption in chiral samples. The high sensitivity of this technique resides in the use of "twin" pulses to account for energy and mode fluctuations of the excitation pulse when determining absorption nonlinearities as a function of the light polarization. The robustness of this method was validated by measuring the first ever reported two-photon absorption circular dichroism (2PA-CD) spectrum on a chiral binaphthol derivative in solution. Finally, Chapters VI and VII compile an ample experimental and theoretical investigation of the chirality-dependent 2PA of axial enantiomers in solution. We combined the use of the synchronized double L-scan technique with state-of-the-art density functional theory calculations to provide a precise and reliable description of the contribution of the different electronic excited states to the 2PA-CD and 2PA-CLD spectra. Our findings are foreseen to have a tremendous impact in the comprehension of some of the most fundamental aspects of chiral phenomena.

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The aim of this study is to analyze radiation from surface currents lying on an interface between a grounded, planar, lossless, isotropic, chiral slab and a simple lossless dielectric half-space. An eigenvalue-eigenfunction approach, specifically the Ohm-Raleigh method, is employed to obtain a modal expression for the full-wave Green's function. By using asymptotic techniques, the far-field electric field is found for an elemental point dipole source. The theory is directly applicable to radiation from a printed circuit antenna having a chiral substrate. Current research efforts show that under certain circumstances, the introduction of chiral materials as substrates of microstrip antennas offers novel radiation properties over achiral microstrip antennas. A number of representative antennas are analyzed with respect to radiation pattern, main beam position, and directivity. / Master of Science