Theoretical Studies On The Photophysical Processes Of 1,8-naphthalimide Fluorescent Probes

1,8-Naphthalimide derivatives are one of the fluorescent compounds which are earilier studied and widely application. They have been widely used in the field of fluorescent probe and attracted immense interest owing to their simple structure, good light stabilities, high fluorescence quantity yield, sensitive to environment and the diversity of structure modification.In this work, the geometric and electronic properties of 1,8-Naphthalimide derivatives are investigated by quantum chemical calculations, including the structures and properties of the excited states, the mechanism of the daul fluorescent discussion, and the effects of the substituent and solvent on the molecular structure and on the absorption and emission spectra. The relationship between the molecular structures and potophysical properties is discussed. It is envisaged that our calculations may be of assistance in the design of new fluorescent probes.Firstly, we introduce the reaction mechanism of the fluorescent probe, meanwhile, the classification and development of 1,8-Naphthalimide derivatives fluorescene probe are discussed.Furthermore, the theoretical calculation methods applied in this work are introduced briefly. Mainly include Hartree Fock approximation, density functional theory (DFT), time-dependent density functional theory (TD-DFT) and the single configuration interaction (CIS) method.In the third chapter, the structures and absorption spectra of the 1.8-naphthalimide fluorescent pH probe molecule Napa-pp and its reference (Nap-pp, Napa-p and Nap-p) are studied with DFT and TDDFT methods. The results show that for the ground state of the neutral probe molecules Napa-pp, HOMO-2 and LUMO are locted on the fluorophore, while the HOMO is located on the whole piperidine phenyl unit and HOMO-1 is located on the alkylamine unit. It will be possible to produce PET and ICT effects and cause fluorescence quenching. Upon the addition of H+, the alkylamine N atom is protonated in the form of NH+, the HOMO energy of alkylamine unit becomes lower than that of the excited fluorophore moiety and the LUMO energy of alkylamine unit becomes higher than that of the excited fluorophore moiety, leading to a PET quenching process form the alkylamine unit to the fluorophore and the fluorescence is intensified when compared with the neutral Napapp. When the piperidine N atom is protonated in the form of bis-protonated Napapp, both the HOMO and LUMO are located almost completely on the naphthalimide moiety, so there is no ET from the alkylamine unit to the fluorophore and ICT from the piperidine phenyl to the fluorophore, leading to an intensive intrinsic fluorescence from the naphthalimide moiety of this compound. The calculated results have showed a good agreement with the experimental data.In the fourth chapter, the absorption and emission spectra of 21 4-phenyl-1,8-naphthalimide derivative are studied by DFT, TD-DFT and CIS methods. The effects of electron-donor (electron-aceeptor) substituents and solvent polarity on the order of localized excitation (LE) and intra molecular charge transfer (CT) excitation have also been studied. The molecular orbital analysis shows that, with the enhancement of the electron donating ability of the substituents on the phenyl, the order of LE and CT has been changed, and the fluorescence can be quenched in a more smaller polar solvent. The mechanism of daul fluorescence for the compound 4-MeOPhONI are studied by the twisted intramolecular charge transfer (TICT) model.In the fifth chapter, the stable structures of local excited (LE) and charge transfer (CT) states for FluONI are optimized by CIS method. The results show that the strongest absorption and emission spectra are of charge transfer (CT) feature, the calculated properties of FIuONI in spectra suggested that it has potential application value in the field of new fluorescent materials, nonlinear optical materials etc.In the sixth chapter, the reaction H2+ CH3â†'H+CH4 has been investigated with an eight-dimensional (8D) time-dependent wave packet quantum dynamics method in which the CH3 group keeps its C3v symmetry in the reaction. The reaction probabilities, integral cross sections and thermal rate constants in the temperature range of 200-2000 K are calculated. Vibrational excitation of the H2 and CH3 both enhance the reaction probability, but the vibrational excitations of H2 have bigger effect on the reaction probability than those of CH3. The quantum dynamical rate coefficients are in reasonably good agreement with the experiment measurements and other theoretical calculated values.The last chapter is the summary.