| The emergence of laser promotes kinds of new nonlinear optical phenomena to be found, making the rapidly development of nonlinear optics. Among the various nonlinear optical phenomena, two-photon absorption is a hot topic due to its widely usage in the fields of chemistry, biology, physics, materials science, especially in the area of two-photon fluorescence microscopic imaging. Looking for new materials with strong nonlinear optical properties becomes more and more important. In this context, organic molecular materials, which show advantage in wide response band, short response time, high optical damage threshold, good flexibility and processing, exhibit attractive prospect. Quantum chemistry calculations based on ab-initio can effectively describe the optical properties of molecular system and provide information on the design and synthesis of novel molecular materials. However, the calculation is only based on the molecular structure, ignoring influence of laser on the medium. This brings difficulty in the comparison between the calculated result and experimental measurement. Thus one should take the interaction between laser and matter into consideration. The present thesis mainly includes researches on two aspects: one is to investigate the dynamical process of laser propagation in organic molecular medium by numerically solving the Maxwell-Bloch equations using an iterative predictor corrector finite difference time domain technique, the other is the theoretical calculation on a series of fluorescent probes. The main contents and results are illustrated as follows: Ⅰ. Theoretical study on optical limiting property1. Optical limiting property of 4,4’-bis(di- n-butylamino) stilbene(BDBAS)The pulse with time domain of femtosecond propagation in the molecular medium BDBAS is studied by solving the Maxwell-Bloch equations, and optical limiting property of the medium as well as dynamical two-photon absorption cross section is investigated.(1) The numerical results show that the medium possess excellent nonlinear optical peoperties. And the optical limiting of BDBAS depends crucially on the thickness and density of the medium. Dynamical two-photon absorption cross section is enhanced as the increase of pulse width and propagation distance.(2) When the two-color ultrashort laser pulse propagates in BDBAS, the electric field and corresponding spectrum change obviously. The optical limiting performance is weaker and dynamical two-photon absorption cross section is smaller with the increase of delay time between the two sub-pulses. The results indicate that one can modulate the nonlinear optical properties of the medium by controlling the delay time of the two-color pulse.(3) The propagation of chirped pulse in BDBAS is simulated. Our numerical results show that the spectra of the electric fields exhibit obvious carrier frequency shifts with the presence of chirp. Besides, both the optical limiting and the dynamical two-photon absorption are influenced by the laser chirp.(4) The effect of static electric field on the propagation and spectrum of the ultrashort laser pulse in BDBAS is studied. The research results show that split of the pulse is enhanced and even-order spectral components are generated when a static electric field is present. In addition, optical limiting behavior becomes obvious and dynamical two-photon absorption cross section is larger with the intensity of static electric field increases.2. Optical limiting property of porphyrin and phthalocyanine compoundsThe pulse with time domain of nanosecond or picosecond propagation in porphyrin and phthalocyanine compounds is studied by solving the coupled rate equation-field intensity equations, and optical limiting property of the compounds as well as dynamical two-photon absorption cross section is investigated.(1) Optical limiting properties and dynamical two-photon absorption of a series of newly synthesized porphyrins and their graphene oxide composites are theoretically analysed. The results show that composites exhibit enhanced nonlinear optical properties in comparison with individual porphyrins. Central metal plays important role in the performances of the compounds. Further investigations show the influences of medium thickness and pulse width on two-photon absorption cross sections.(2) Propagation of a picosecond pulse trains in free-based tetrapyridyl porphyrin H2 TPyP with Ruthenium outlying complexes and nonlinear optical properties of the compounds are investigated. The computational results show that outlying Ruthenium groups can influence the optical limiting properties of the medium, which are in reasonable agreement with the experimental ones. Further analysis indicates a method of modulating nonlinear optical absorption properties of the medium by changing parameters of the pulse train.(3) Propagation of long pulse with transverse distribution of Gaussian form in chloroindium phthalocyanine is simulated, and the optical limiting as well as dynamical two-photon absorption performance is studied. The effect of substituent position is discussed, showing that the compound with α-substituent has preferable optical properties. The results are in reasonable agreement with the experimental measurements. Moreover, the ab-initio calculations are performed to investigate the mechanism of substituent effect on nonlinear optical properties of the compounds. Ⅱ. Theoretical study on two-photon fluorescent probe1. Intramolecular charge transfer-based two-photon fluorescent probeOne-photon and two-photon absorption, as well as fluorescent emission properties of a series of 2-(2’-hydroxyphenyl)benzoxazole(HPBO)-based derivatives are studied by use of the response theory. Their evolutions on the optical properties response to zinc ion and p H are specially emphasized. The charge transfer process for the charge transfer state is displayed, indicating the mechanism of these probes to be intramolecular charge transfer.2. Photoinduced electron transfer-based two-photon fluorescent probePhotoabsorption and photoemission of the newly synthesized two-photon fluorescent probes QNO and LNO in the absence and presence of nitric oxide are studied. Effect of fluorophore on the sensing performance is discussed. Importantly, responsive mechanism of these probes is analysed by use of distributions of molecular orbitals, showing the photoinduced electron transfer process.3. Energy transfer-based two-photon fluorescent probeThe absorption and emission properties of a series of fluorescent probes containing rhodamine moiety are investigated theoretically by employing the time-dependent density functional theory as well as analytical response theory. Analysis of molecular orbitals is presented to explore the responsive mechanism of the probes.(1) Linear and two-photon absorption, as well as fluorescent properties of a newly synthesized fluorescent probe for sensing H2O2, NO and H2O2/NO are studied. Calculated results indicate that the photoabsorption and photoemission properties show drastic changes upon reacting with detected objects. The calculated results are in reasonable agreement with the experimental ones, suggesting the compound to be a potential candidate for two-photon fluorescent probe. Moreover, responsive mechanism of the probe is investigated by analysing the molecular orbitals, which is proved to be the fluorescent resonance energy transfer.(2) Optical properties of a newly synthesized through-bond energy transfer-based fluorescent probe Pro1 are analyzed with and without the presence of copper ion. The available experimental measurements are elucidated. Two compounds of Pro2 and Pro3 with different donors of Pro1 are design to investigate the donor effect on sensing performance of the probes. In addition, an experimental fluorescent ratiometric chemodosimeter Pro4 with similar donor and acceptor of Pro3 but with different connections between the donor and acceptor is also investigated. Responsive mechanisms of the probes are explored by analyzing molecular orbitals, which theoretically demonstrates the through-bond energy transfer process.This paper is organized as follows. The first chapter reviews the development of nonlinear optics and also the laser technology. A brief introduction on the developing process of two-photon absorption and optical limiting materials, as well as two-photon fluorescent probe is given. In the second chapter, theory of the interaction between laser and matter are introduced. The Maxwell-Bloch equations and the derived rate equation-field intensity equation within slowly varying envelope approximation and rotation-wave approximation are presented. Numerical method used in this paper is elucidated in detail. Different approaches of calculating two-photon absorption cross section of molecule are summarized in the third chapter, including sum-over-state, few-state model, finite field, and response theory methods. Also the methods of representing the solvent environment are presented. In the fourth chapter, optical limiting and two-photon absorption properties of BDBAS are introduced, and the influence of chirp rate as well as static field on nonlinear properties of the compound is given in detail. Optical limiting properties of a series of porphyrin and phthalocyanine compounds are presented in the fifth chapter. From the sixth chapter to the eighth chapter, study works on fluorescent probe based on responsive mechanism of intramolecular charge transfer, photoinduced electron transfer, fluorescent resonance energy transfer and through-bond energy transfer are collected. In the last chapter, the conclusions and prospect are given. |
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