An Investigation On The CIDEP Of P-benzoquinone,Acetone In Different Systems And The Theoretical Calculation Of RTPM

The phenomenon of transient populations in electron spin states deviating from the Boltzmann distribution has been known as chemically induced dynamic electron polarization (CIDEP), which can be tested by time-resolved ESR (TRESR). CIDEP can give us more information about photochemical and photophysical processes and it is a useful method to study intermediate species, electron transfer and energy transfer mechanisms in reactions.In this paper, based on the brief summary of the fundamental theory of electron spin polarization, the contributions from triplet mechanism(TM) and radical pair mechanism (RPM) to the CIDEP of p-benzoquinone/ethylene glycol (PBQ/EG) system was quantitatively analyzed. The CIDEP of laser photolysis of PBQ and acetone in different homogenous solutions and micelles solutions were experimentally studied. At the same time, considering the zero-field-splitting constant E, the electron spin polarization due to radical-triplet pair mechanism (RTPM) is theoretically calculated in detail.In chapter one, the fundamental principles of ESR and the definition of CIDEP as well as its current development were described respectively.In chapter two, the four mechanisms to generate CIDEP were introduced and the experiment instrument was described briefly. The CIDEP spectrum of PBQ/EG system has been obtained experimentally by using 285nm laser photolysis. Compared with the stimulated spectra, the relative CIDEP intensity from TM and RPM at different time delay was quantitatively analyzed. It was concluded that the polarization of p-benzosemiquinone radical PBQH* produced from TM decayed faster than generated from RPM.In chapter three, the CIDEP of the photolyzed radicals of PBQ and acetone in different homogenous solutions were experimentally studied and the influence of micellar microenvironment on the generation of CIDEP were discussed.The major peaks of PBQH' generated from TM was obtained inPBQ/propylene glycol (PG) system and the proton exchange phenomenon was observed with the addition of H2SO4. In PBQ/formamide (FM) system, only the five hyperfine peaks of PBQ- were obtained and the six double peaks of PBQH appeared with the addition of H2SO4 which indicated PBQ- was formed from the dissociation of PBQH*.When the acetone/EG (PG) system was photolyzed, the E/A pattern CIDEP spectrum of (CH3)2COH and CH2OHCHOH( CH3 COHCHOH ) generated fromRPM were obtained. In acid environment, the signal of CH2OHCHOH(CH3 COHCHOH) decreased evidently. In basic environment, (CH3)2CO- wasproduced.In micellar microenvironment, different surfactant and different concentration have different influence on CIDEP. With the addition of CTAB to sample solution, the polarization mechanism and the signal intensity were the same as in homogenous solutions. When PBQ/PG/TX-100 micellar solution was irradiated by the laser, the CIDEP signal of PBQ- was obtained except for the signal of PBQH'. When ACETONE/EG (PG) /TX-100 micellar solution was photolyzed, the TM appeared accompanying the RPM and the relative ratio oi'TM to RPM increased with the increasing of TX-100 concentration. Here, the fluence of micellar invironment on the generation of CIDEP was simply discussed and analyzed.In chapter four, based on the angular momentum theory, the second-order pcrLurbation theory and the motion equation of density matrix, the polarization intensity on the stable radicals of the QP-RTPM and DP-RTPM, with the zero-spilling-field constant E involved in the Hamiltonian, were calculated in detail, respectively. The results indicated that the polarization pattern is E+E/A or A+A/E. Furthermore, the results indicated that the zero-spilling-field constant E made the net polarization decrease and the hyperfine-dependent polarization increase.