| Spectroscopy was an important method to characterise the interaction between matter and light and characterise the structure and the dynamics of matter. When elec-tromagnetic radiation acts on the material, the material would produce a response to the field and the relationship between the response and the wavelength of the light be-came the spectrogram. There exists many different kinds of interaction between the electromagnetic radiation and matter which lead to varies of spectroscopies such as ab-sorption, emission, reflection and scattering and so on. Different spectral techniques are applied to study and checking different materials and processes.In modern chem-istry, spectroscopy has become the main tool to determine the molecular structure and properties. We can obtain the spectra not only through the experiment spectrometer but also by the theoretical calculation. However, the experimental spectrum can not directly provide the information about the molecular structure and corresponding dynamics. In addition, the thermal fluctuation, molecular environment and the inherent nature of the system itself would produce complicated influences on the spectrum. The experimen-tal technology is difficult to separate those effects and evaluate them. Therefore, sci-entists combined several experimental spectroscopy technologies and simultaneously introduce the theoretical calculation. By comparing the theoretical and experimental spectrum and referencing the micro information generated during the theoretical cal-culation, we can better understand the physical structure, the dynamics and the effects of the external environment contained in the experimental spectrum. Nowadays, this method by combining the theory and the experiment is gradually becoming the most powerful and reliable way. Because the theoretical calculation can not only support and supplement the experimental results, determine the initial and final structure of the target molecules and the corresponding the electronic coupling, predict the molecular properties but also analyze and quantitatively give the contributions of different effects in a molecular or a supramolecular system. For these reasons, computational spectra are fast becoming mark experimental spectra and the basic tools to explain the fundamental physical and chemical processes.Although, the theory about molecular spectrum calculation was established early and the corresponding methods have made great progress, a powerful and user-friendly interface of multi-virtual-frequency molecular spectrum calculation tool does not exist. Especially, when the theoretical spectrum method is applied to calculate the molecular or the supramolecular system of interest of the current science and technology, we face a greater challenge. With the development of modern technology, the researchers need to control more and more complicated systems, such as biological molecules, nano ma-terials, molecular-complex interface, in a covalent bonding of the weak force up the complex and orderly, and have specific functions of molecular aggregation, etc. Tradi-tional initio quantum chemistry method and quantum dynamics method cannot be used to simulate this kind of complicated system for that the calculation-consumed time has increased dramatically as the molecular scale increases. The difficulty of the theoretical calculation of the spectrum is not only the need to calculate the molecular geometry, the electronic structure and the dynamic process of ground state and excited state but also the need to consider the actual complex molecular environment such as the solution, protein microenvironment, semiconductor and metal interface and so on.The two-photon absorption phenomena of fluorescent proteins have fascinating applications in bioimaging and medical technology as biomarker, biosensor, and even in communication technology. Fluorescent proteins are widely used in two-photon laser scanning microscopy, which can penetrate deeper tissue with less damage. There-fore, the scientists have performed a large amount of experimental studies to investigate which proteins are the brightest and what are the best excitation wavelengths. However, due to competing optical processes such as stimulated emission and scattering that arise in high-intensity regime in herent in these experiments, it is difficult to experimentally measure the absolute TPA cross. In biological systems, there are additional calibration difficulties leading to significant discrepancies in the reported measurements of abso-lute TPA cross sections. It is thus essential to theoretically calculate the TPA cross sections to assist experimental studies for describing the microscopic excited-state dy-namics, explaining the experimental results and designing new materials with desired non-linear optical properties as well.The hybrid system composed by molecules and nanoparticles have been found in nanoscale devices, photovoltaic solar cells and surface enhanced optical signal appa-ratus, etc. In these systems, molecules or the semiconductor exciton can interact with the plasmons generated by the metal nanoparticles which can lead to many novel phe-nomena, such as nonlinear Fano effect, Rabi oscillations, etc. The surface dipole pro-duced by the plasma excitation can greatly enhance the optical signal of the adsorbed molecules and strengthen the energy transfer between the molecules or semiconduc-tor and the nanoparticles. At the same time, the molecules adsorbed near on the sur-face can also be used to control the conduction behavior between nanoparticles of the Plasmon. For example the current widely used SERS technology, it just utilize the signal enhancement effect of the plasmon of the noble metals nanoparticles to the ad-sorbed molecules. Experimenters and theorists have reached a consensus to the surface strengthening mechanism and conclude that it is ascribed to two kinds of mechanisms: one is electromagnetic field enhancement, and the other one is the chemical enhance-ment. Now, the surface enhancement optical signals have been widely used in signal detection, molecular recognition and solar cell manufacturing field and so on. As for the complexity of the interactions among the molecules, the metal nanoparticles and the light, a unified method has not been found to well describe both two mechanisms si-multaneously and quantitatively calculate the contributions from the two mechanisms. However, Compared with the chemical enhancement effect, the description of the elec-tromagnetic enhancement effect is relatively easy. Because people have developed a series of effective numerical electrodynamics methods to calculate the surface local area and many combination methods to simultaneously solve TDDFT/TDHF and Maxwell’s equations. As to the description of chemical enhancement effects, there are two ways to deal with it. One is that molecules are assumed to be adsorbed on a small metal clus-ter and such mature method can be used to calculate the spectrum of molecule-cluster system. However, as small metal cluster is far different from the real system, the cal-culated results can not be compared with the experimental data. The other way utilized Anderson-News type Hamiltonian to describe the charge transfer between molecules and the metal nanoparticles, which is associated with the empirical parameters of the system. Therefore, developing a first-principle method suitable for real open electronic systems is of great fundamental significance to the biological technology, signal exam-ination and the progress of energy and materials science.The main work of this paper is focused on developing and utilizing the time-dependent correlation function method to study the two-photon absorption spectrum of several fluorescent protein chromophores and the surface enhancement behavior of the molecular optical signal. In addition, the Herzberg-Teller (HT) vibronic coupling effects and the influences produced by the interfacial energy transfer process and the interfacial charge transfer process on the spectrum signal are also investigated. The corresponding results are shown as follows:(1)The OPA and TPA properties of three FP chromophores (a neutral chromophore in enhanced cyan fluorescent protein (ECFP) and two anionic FP chromophores in DsRed2 and TagRFP) have been investigated in detail and the corresponding pure elec-tronic and vibrationally-resolved electronic spectra have been calculated. And the con-tributions from the Franck-Condon (FC) scattering and Herzberg-Teller (HT) vibronic coupling effects are analyzed. We demonstrate that the HT effect leads to the blue shift of TPA maximum relative to OPA maximum on the low-frequency absorption bands for two anionic chromophores. The intramolecular charge-transfer character of higher-lying excited states explains the phenomenon that TPA spectra in higher-frequency re-gion are much stronger than those in low-frequency region.(2)The time-dependent correlation function method, proposed by us recently, is expanded to calculate RRS for an organic molecule absorbed on an inorganic semicon-ductor surface and investigate the dynamics behavior of the interfacial charge trans-fer. Localized molecular excitation and photoinduced intermolecular charge transfer excitation are both aken into consideration. The results demonstrate that the bidirec-tionally interfacial CT significantly modifies the spectral line shapes. The constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT.(3)Developing a time-dependent correlation function method to investigate the surface enhancement phenomenon of the optical signal of the molecular-inert metal nanoparticles system. We utilize classical Hamiltonian model of the photon-exciton-plasmon system to describe the surface enhanced Raman spectroscopy (SERS) and the electronic transfer and energy transfer process between the molecules and the nanopar-ticles.The content of the thesis include six parts as follows:Chapter one is the introduction part, mainly introducing the background and sig-nificance of the research.Chapter two shows the development history of nonlinear optics. This part de-fines the nonlinear polarizability and deduced the formulas of one-photon absorption spectra, two-photon absorption spectrum and resonance Raman spectra based on the perturbation theory. The spatial domain formulas of the spectra mentioned above are changed into time domain by green function, which avoids the complexity of sum-of-state method. This part also provides the vertical gradient approximation and the cor-responding simplified expression of propagator. Then, the time-dependent approach of resonance Raman spectra is modified and further deduced for applying to the system composed by the organic molecule absorbed on the semiconductor.Chapter three describe the calculations of the two-photon absorption spectrum of three kinds of fluorescent proteins chromophore.The experimentally-measured two-photon absorption(TPA) spectra of fluorescent proteins (FP) show quite different char-acters with one-photon absorption (OPA) spectra in both the low-frequency and high-frequency regions. To unveil the mechanism which results in the discrepancies between OPA and TPA spectra, and obtain the fundamental structure-property relationships of FPs, here we conduct a theoretical study on OPA and TPA properties of three FP chro-mophores including a neutral chromophore in ECFP and two anionic FP chromophores in DsRed2 and TagRFP.Chapter four presents the calculations of resonance Raman spectra of the organic molecule absorbed on the semiconductor in order to investigate the charge transfer process. The time-dependent correlation function approach for the calculations of ab-sorption and resonance Raman spectra (RRS) of organic molecules absorbed on semi-conductor surfaces is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles.Chapter five introduces surface enhanced resonance Raman spectra and the corre-sponding interfacial charge transfer dynamics of the molecules/inert metal nanoparticles system. The time-dependent relevant functional method utilized in the work before is expanded to calculate the resonance Raman spectra of the molecules adsorbed on the metal. In order to reveal the reasons of the enhancement, we would adjust the interfa-cial parameters to investigate the changes of the spectrum shape and relative strength of resonance Raman and the changes of the corresponding interfacial charge transfer dynamics.Chapter six shows a brief summary and forecasting on the related filed. |
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