Theoretical Studies on Electronic and Vibrationally Resolved Multi-Photon Absorption and Dichroism
|Course||Materials Physics and Chemistry|
|Keywords||Linear and Nonlinear Optical Electronic vibrational spectroscopy Solvent effect|
By studying the interaction of light and matter, we can better understand the physical world around them. Traditional light source, only linear optical phenomena observed since the advent of the laser, nonlinear optics developed rapidly as a new discipline in modern laser technology, optical communications, data storage, optical information processing shows attractive prospect. Looking for strong nonlinear optical properties and the response speed of the new materials become one of the main topics of this area. In essence, any material having nonlinear optical properties, while the linear particular case approximation. As the nonlinear optical material of the organic molecules is easy synthesis and processing, broad response band, in response to the short time, and such characteristics much attention. The quantum chemical calculations can provide valid information, and the molecular structure of its optical response link. Theoretical research can theoretically design a new type of molecular materials to guide experimental synthesis, improve the efficiency of the experiment. This thesis focuses solve two problems: theoretical and experimental results in the comparison process solvent environment and the impact of molecular vibration. Most theoretical studies are conducted for a single molecule, and the experimental measurement of the optical properties of the molecular materials is generally conducted in a solvent, the surrounding solvent molecules may have an important impact on the structure and optical properties of the solute molecules, which In comparison to the theoretical and experimental measurement results makes it difficult. Accordingly, in order to better compared with the experimental, the need to consider the environmental impact of the solvent in the theoretical model. This thesis polarizable continuum model (PCM) to simulate the solvent environment, uniform solvent as a continuous dielectric, characterized by the dielectric constant. When the presence of external electromagnetic fields, the solvent molecules affected by an induction field, the induction field, in turn, will shield the applied electromagnetic fields, this part of the effect can be described by the so-called local field factor. In addition, based on the theoretical study of the vertical transitions only consider the transitions between electronic energy levels, ignoring the contribution of vibrational levels, many experiments often contains fine vibrational structure commenced, in addition, there are a lot of important experimental phenomena may be hidden in fine vibrational structure, only to consider the impact of molecular vibration to make the right theoretical explanation. Therefore, the correct understanding of the molecular vibrational spectroscopic properties are also very necessary. The complexity of the vibration coupling theory, the difficulty of constructing theoretical models and a large amount of calculation allows the study of the molecular vibrations less. This article based on the adiabatic approximation and the harmonic approximation cornerstone of two theoretical studies of the electronic vibrational spectra. The adiabatic approximation assumes that the movement of electrons and nuclear motion can separate them more reliable description of the excited level far away from the other level, the adiabatic approximation. Harmonic approximation is one of the commonly used and effective introduction of molecular vibration effect approximation of the approximation of the atom as a small ball (resonator), the quality of the chemical bonds between atoms as negligible spring. The thesis is using two adiabatic simple harmonic motion model: A harmonic adiabatic Franck-Condon (AFC) model based on optimized initial and final state of equilibrium configurations, given the high-resolution electronic-vibrational spectra, and can effectively identify the characteristic peaks. Another linear coupling model (LCM), can only provide low-resolution spectra, but to avoid the usually cumbersome configuration optimization of excited states, and can describe the main features of the electronic vibrational spectra. With the emergence of high-power laser, multi-photon spectroscopy has become a hot topic, and has important applications in the field of biology, chemistry, materials science, and physics. Due to different selection rules, the multi-photon spectroscopy can be given a single-photon spectroscopy did not give a new vibration or electronic transition state. Multi-photon absorption spectroscopy to study the molecular structure of the main analytical tool, one of the papers focus on the study of charge transfer organic molecules single (OPA), double (TPA), three (3PA) photon absorption properties. Circular dichroism spectroscopy, based on the left and right-handed circularly polarized light absorption properties different, can be regarded as a special kind of an absorption spectrum of a chiral nature. We have focused on single chiral molecules (ECD), the double photon circular dichroism spectroscopic properties (TPCD). The thesis can be roughly divided into two parts: the first electronic transition spectrum, that is, only consider the transition of the electron energy levels, regardless of vibration dynamic contribution; considering electronic, vibrational levels of contribution, namely electronic the study of the vibrational spectra. A brief overview of the main contents of the thesis. An electronic vertical transition spectra of (1) organic conjugated molecules multiphoton absorption properties of the semi-empirical quantitative research. (Paper 1,2) multi-photon absorption cross section of the most direct method is to state the summation formula (SOS), in ab initio level using the state summation method to handle very large computational molecular system, it is generally in the semi-empirical level. This paper, using the semi-empirical ZINDO program, combined with configuration interaction (CI) method, calculated the transition dipole moment between the state summation formula required molecular transition energy, dipole moment, and the state-state, first obtain the nonlinear susceptibility, further calculate the the material molecule multi-photon absorption cross section. This semi-empirical method enables the accuracy of the calculation is restricted, but that can not be achieved in the ab initio level larger molecules, it becomes possible by the system of multi-photon absorption properties. The semi-empirical method has been used extensively for the calculation of the nonlinear optical properties of different types of molecules, to be able to more accurately predict the trend of the molecular nature QSAR study has important implications. This thesis is focused on the build and test a reliable theoretical system, so choose a medium-size molecules studied. Articles 1 containing imidazole - thiazole nucleus Y-shaped molecules in single, double, three-photon absorption properties of systems research results to verify the experimental conclusions, pointing out that the study of the molecular potential of multi-photon absorption materials . The molecular nature of the multi-photon absorption is increased as the electron donor intensity increase. The study found the heterocyclic core due to its rich electronic properties, can provide more free electrons to enhance the intramolecular charge transfer, which can enhance the strength of multi-photon absorption. In addition, the Y-type design and the sulfur group as an electron acceptor are enhanced multiphoton absorption plays an important role. Paper 2 a series of trivalent boron receptor D-π-A-type organic compound, two-photon absorption properties were studied. The study shows that trimethylbenzene can be well protected trivalent boron to make it independent of oxygen in the air attacks. As long as a large group of the trivalent boron protect, it can be very effective electron acceptor. Based on geometry optimization of the molecular two-photon absorption intensity and peak position reported. (2) organic conjugated molecules First principles study of multi-photon absorption properties. The three-photon absorption (thesis) belongs to the fifth-order nonlinear optical behavior, but can be obtained by the third-order response function of a single residue derived from third-order transition matrix element. Thesis 3 is the first application of the third-order response field theory with the polarized continuum model of a high-conjugate A-π-π-π-A symmetrical the of fluorene - Derivative body three-photon absorption nature as well as solvent effects. Detailed description of the solvent environment, and the molecular configuration (especially the plane of the molecule) of the influence of the absorption properties of the article. The study shows that, compared with the gas phase, the polarity of the solvent increases to a large extent the value of three-photon absorption cross-section. Room temperature, the molecules may be present a variety of configurations that correspond to the different dihedral, rather than a single-balanced configuration, therefore, only for the calculation of the single configuration is not sufficient. For large-size system, using the complete response theory methods so that the amount of calculation becomes large, a small state model calculation amount much smaller. The study found that the two-state model, we study the system, not the nature of the three-photon absorption good description of the results and a complete response theory results vary greatly. In addition, this paper, we will calculate the results with experimental data to carry out a detailed comparison. 4 (3) chiral molecular single-and two-photon circular dichroism spectra First-principles study (paper 4,5). Papers, based on first-principles density functional theory combined with non-origin-dependent response function R-()-3-methyl-cyclopentanone (R3MCP) molecular single, two-photon circular dichroism spectra of a theoretical study. The two lowest energy configuration, comprehensive analysis and comparison of single-and two-photon circular dichroism spectra, and its strength and characteristics of two-photon absorption compared. Geometry, calculation of the basis set, exchange relevant functional and detailed discussion. The results show that the the recent developments CAMB3LYP exchange-correlation functionals can be better than the commonly used B3LYP functional Rydberg states described the resulting spectra in good agreement with the experimental. The article from the point of view of molecular orbitals to characterize the nature of the excited-state transitions, and single, the different response of the two-photon process made construed accordingly. Papers 5 are given for the first time an axial chiral molecule R-() -1,1 '-Bi (2-naphtol) (RBN) and its enantiomer S-(-) -1,1' as-bi (2-naphtol) (SBN) the TPCD experimental spectrum in a solvent. The spectrum measured by DoubleL-scan technology, given the theoretical results. The experiments are given corresponding to the left and right-handed circularly polarized light of TPA spectrum, the difference between the two i.e. TPCD spectra is given. With the expected results of the same experiment is clear that mirror enantiomers TPCD Spectroscopic Properties rendered completely opposite, i.e., signal. The research system TPCD spectroscopy show their ECD different characteristics, thus providing a good example to illustrate the TPCD can play a very good complementary role ECD chiral recognition, is a promising chiral recognition tools. The good derived on in B3LYP/PCM level TPCD spectrum to repeat the type of experimental spectra. Exists only between two mutually perpendicular naphthol weak interactions that lead appears many degenerate state, the 25 calculation takes into account the contribution of excited states in order to cover the experiment given spectral range of 200-350 nm. The calculations also show that the nature of the system TPCD very sensitive to impact on the environment of the solvent, along with the changes in the signal symbol. It can be found that the main characteristic peaks of the experimental spectra are from different excited states of positive and negative signals cancel each other role. , The electronic vibrational spectroscopy study (1) the effects of vibration on single, two-photon absorption properties of affected first-principles study (paper 6,7) papers 6 Application LCM vibration model combined with density functional response theory of a D-π- the stilbene derivative molecules of D-type single-, two-photon electronic vibration nature to do the system gives the lowest four excited states contribution of Franck-Condon, Herzberg-Teller contribution, as well as the total electronic vibrational spectra, respectively both 0.1eV and 0.01eV Lorentz broadening coefficients. First different optimization methods render the molecule to a different plane, the results showed that the density functional method makes the molecule tends to planarize, Hartree-Fock better describe the molecular structure. 0.01eV spectral broadening coefficient, it is clear that more single-photon absorption fine structure of electronic vibrational spectra calculated 0-0 transition is the most important transition, and vibrational levels higher than 2 can be safely ignored out, and not be calculated results. Corresponds to the CNC and CCC distorted vibration mode is the main contribution. Also elaborated the Herzberg-Teller contribution famous \This work belongs to the first application of the linear coupling model different molecular excited states of a single, two-photon absorption electronic vibration spectra. Franck-Condon level, the single of the same molecule, two-photon absorption spectrum should have the same type of spectrum, the single given experimental vibrational spectra of two-photon absorption electronic but usually there are differences. Papers 7 combined density functional response theory and linear coupling model vibration contribution of Franck-Condon and Herzberg-Teller mechanism analysis, pointed out that the difference brought by Herzberg-Teller effects of vibration. The theoretical mechanism successfully explains the single of a heterocyclic molecule, the offset between the two-photon absorption maximum peak, and can be extended to have a different single the general molecular state of the two-photon absorption. Also worth mentioning is that the papers belonging to the first comprehensive consideration of the the electronic vibration coupling and solvent effects on the two-photon absorption spectra, in which the solvent effect polarizable continuum model simulation. (2) chiral molecule single-photon circular dichroism electronic vibration spectra of first-principles study (paper 8,9). Experiment gives R3MCP molecular vibrational levels expanded ECD spectrum papers 8 LCM model electronic vibrational coupling effect of the chiral molecules ECD spectra and full account of the Franck-Condon and Herzberg-Teller vibration contribution. The study showed that the latter can lead to a single electronic state contrary to both positive and negative signals, causing the molecular chirality in response to changes in the nature. This shows that the theoretical calculation of the circular dichroism consider only vertical transitions may result in positive and negative signal error, vibration effect is very necessary. Circular dichroism signal is always the opposite sign criterion, often experimental circular dichroism signal as the characterization of the molecular configuration of chiral enantiomers. The results undoubtedly important guiding value related experiments. In order to identify more accurately the experimental peaks, the paper to be able to give a high-resolution spectra AFC vibration model, an accurate description of the ground state of the Excited State Potential energy surface, based on the full account of the Franck-Condon Herzberg-Teller normal-mode The Duschinsky rotation frequency of contribution and may change in the circular dichroism of chiral molecules, respectively, and a detailed discussion of each contribution item. The method of the fine structure of the vibration accurately identified. The circular dichroism signal strength will be reduced as the temperature increases, this is consistent with experimental conclusions. It is worth mentioning that the study further confirmed the the LCM model predicted a single electronic states in the positive and negative signal changes. However, due to signal changes occur in the Axial configuration, and Equatorial configuration Boltzmann configuration ratio of only 1:9, which limits the theoretical predictions given by the article to obtain experimental verification of the possibility. (3) chiral molecular two-photon circular dichroism electronic First-principles study of vibrational spectra (Thesis 10) Recently, the chiral molecules TPCD spectrum of experimental research has made great progress, TPCD combines the advantages of ECD and TPA in chiral molecular recognition application has great potential, which makes electronic vibrational spectra of TPCD theoretical research also becomes important. Paper 10 combined AFC vibration response model with density functional theory of chiral molecules R3MCP two-photon circular dichroism the electronic vibrational spectroscopy study of the molecule OPA, ECD, TPA spectra compared. Different molecular nature FC level calculated spectrum has the same vibrational level to expand the spectral type of distinction by HT contribution brought. The study found that such more complex optical process for two-photon circular dichroism, FC / HT interference term becomes relatively important, the linear coupling model exhibits limitations in the simulation of a similar nature. For two-photon circular dichroism HT can also be introduced in a single electronic states of both positive and negative signals, and more obvious than the single photon circular dichroism, even with a larger line broadening coefficient and the Boltzmann configuration average The sign of the signal persists, it becomes possible to be verified experimentally. Papers 10 belong to the first two-photon vibrational spectra of electronic circular dichroism studies. In this thesis consists of nine chapters. Chapter Summary First, simple linear optical and nonlinear optical characteristics, and then introduced the related molecular spectroscopy, and focus on the single, double, three-photon absorption, as well as single-, two-photon circular dichroism spectra of the nature , and then the solvent models used in the paper and electronic vibrating spectral theory briefly described. The second chapter a brief introduction to the basic theory of quantum chemistry used in the paper, mainly on the quantum chemical and density functional theory as a starting point to the wave function. The third chapter gives the calculation method of the multi-photon absorption properties, including the time-dependent perturbation theory method (also known as state summation method) and response theory methods. Chapter IV gives the results of the multi-photon absorption properties in the semi-empirical level, namely, a series of Y-type imidazole - thiazole heterocyclic molecules, and a series of trivalent boron receptor conjugated molecules. Chapter 5 gives the results of the study based on ab initio theory of electronic vertical transition spectra, including study solvent effect, two-photon circular dichroism spectra of high conjugated fluorene derivative molecular three-photon absorption properties of chiral molecules single research. The sixth chapter gives the theory and calculation method of electronic vibrational spectra. Chapters VII and VIII, respectively, using the linear coupling model and the harmonic model adiabatic Franck-Condon First principles study of vibrational spectra of molecular electronics. Linear coupling model including electronic vibration coupling effect of the nature of the single-and dual-photon absorption and single photon circular dichroism simulation, based on the adiabatic harmonic Franck-Condon model we focus on single chiral molecules, two photon circular dichroism spectroscopy study. Chapter Summary and Outlook.