光解杜醌/氢给体均相体系的CIDEP研究

以杜醌为光敏剂,用高时间分辨电子自旋共振 (TRESR)波谱仪研究了杜醌/乙二醇体系、杜醌/氮氧自由基/乙二醇体系的化学诱导动态电子自旋极化(CIDEP).实验表明,紫外激光照射下,在杜醌/乙二醇溶液中得到以三重态机理极化为主的中性杜半醌自由基DQH*和以碳为中心的乙二醇碳自由基R*(OH)2的极化信号,而加入氮氧自由基 TEMPO后,则只观测到极化的TEMPO的E+E/A极化谱,其产生机理属于以四重态为先驱的自由基-三重态对极化机理(QP-RTPM),结合极化强度的理论计算对该体系的极化形成过程进行了分析.     

光解丙酮/乙二醇体系的CIDEP实验研究

紫外激光照射下,用时间分辨电子自旋共振(TRESR)波谱仪研究了光解ACETONE/EG体系的化学诱导动态电子极化(CIDEP),得到了丙酮羰自由基(CH3)2C.OH和乙二醇羰自由基CH2OH C.HOH的发射/吸收(E/A)型极化信号,这是一个RPM极化过程.在胶束环境中,不同表面活性剂以及不同的浓度对体系极化的影响是不同的.阳离子表面活性剂CTAB对体系中生成的自由基的极化机理没有产生显著影响,而加入体系中TX-100的浓度对体系的极化机理却产生了很大的影响.在ACETONE/EG体系中,随着TX-100浓度的增加,TM机理对极化强度的贡献明显增大.     

杜醌自由基光化学路径的CIDEP研究

用自制的高时间分辨电子自旋共振波谱仪,测量得到了酸性、碱性和胶束环境下的光解杜醌/乙二醇(DQ/EG)溶液瞬态自由基的化学诱导动态电子自旋极化(CIDEP)谱.在光解均相DQ/EG溶液时,观察到了以增强发射的的中性杜半醌自由基(DQH.)的CIDEP信号;在碱性环境下(pH=9)和TX-100胶束环境下光解DQ/EG体系时得到杜醌负离子自由基(DQ-.)的CIDEP信号;在酸性环境下(pH=2.5)光解DQ/EG体系时,出现的又是中性杜半醌自由基(DQH.)的CIDEP信号.实验结果显示,DQH.由3DQ*与EG之间的氢原子转移反应生成,DQ.-由DQH.的去质子化反应生成,反应中伴随着极化转移.     

丙酮/1,2-丙二醇体系的化学诱导动态电子自旋极化研究

285 nm紫外激光照射下,用时间分辨电子自旋共振(TRESR)波谱仪研究了光解丙酮/1,2-丙二醇(ACETONE/PG)体系,得到了丙酮羰自由基(CH3)2.COH和1,2-丙二醇羰自由基CH3.COHCHOH的发射/吸收(E/A)型极化信号,这是一个自由基对(RPM)极化过程。在酸性环境中,溶剂分子的CIDEP谱明显减弱,(CH3)2.COH的CIDEP谱无明显变化,由此可判断光解ACETONE/PG体系是一个夺氢反应;在碱性环境中,(CH3)2.COH反应生成负离子基(CH3)2.CO-.     

乙二醇均相溶液中苊醌三重激发态淬灭反应的TR-ESR研究

利用时间分辨电子自旋共振(TR-ESR)方法,研究了乙二醇(EG)均相溶液中稳定自由基TEMPO和生物抗氧化剂维生素C(VC)对苊醌(ACQ)激发三重态3ACQ*的淬灭反应.光解ACQ/EG体系,观察到苊醌中性自由基ACQH*和乙二醇烷基自由基的发射/吸收+发射(E/A+E)的CIDEP信号,ACQH*和CH2(OH)CHOH由3ACQ*从EG上夺氢生成.光解ACQ/TEMPO/EG体系,3ACQ*与TEMPO相互作用将极化转移给TEMPO.光解ACQ/VC/EG体系,3ACQ*除了从EG上夺氧外,还从VC上夺氢生成VC负离子基As*-.较强的As*-的CIDEP信号表明VC对3ACQ*有明显的淬灭作用.     

三重态分子/稳定自由基体系超精细相关CIDEP的理论计算

光激发三重态分子/氮氧自由基的乙二醇溶液得到E+E/A极化的CIDEP谱,以光激发三重态与二重态自由基相互作用模型,考虑自由基的超精细相互作用,利用二阶微扰理论及相互作用表象下的密度矩阵,理论上计算了此类体系的CIDEP.     

乙二醇均相及其TX-100胶束溶液中光敏分子菲醌的激光光解研究

用时间分辨电子自旋共振（TR-ESR）和瞬态吸收光谱技术,研究了菲醌在乙二醇均相及其TX-100含水胶束溶液中的光化学反应机理。化学诱导动态电子极化（CIDEP）谱和瞬态吸收光谱都表明,在乙二醇均相溶液中,菲醌光激发三重态3PAQ* 夺取氢原子形成中性自由基PAQH.,三重态机理是CIDEP形成的主要机理。在TX-100含水胶束溶液中,光解主要得到菲醌负离子基PAQ-．,PAQ-．由PAQH.解离形成,解离过程中伴随着极化转移。     

光解对苯醌/甲酰胺体系的CIDEP实验研究

以对苯醌为光敏剂,用高时间分辨电子自旋共振(TRESR)波谱仪研究了对苯醌/甲酰胺体系在酸性、碱性、胶束环境下的化学诱导动态电子自旋极化(CIDEP).光解对苯醌/甲酰胺体系,得到了以苯醌负离子基PBQ·-为主的,同时伴随稍弱的苯半醌自由基PBQH·-的发射CIDEP谱;光解碱性环境和胶束环境下的对苯醌/甲酰胺体系,只得到PBQ·-的CIDEP信号;光解酸性环境下的对苯醌/甲酰胺体系,只得到PBQH·的CIDEP信号.实验结果表明对苯醌负离子基PBQ·-由苯半醌自由基PBQ·解离得到.     

乙二醇均相溶液中苊醌三重激发态淬灭反应的TR-ESR研究

利用时间分辨电子自旋共振（TR-ESR）方法,研究了乙二醇（EG）均相溶液中稳定自由基TEMPO和生物抗氧化剂维生素C（VC）对苊醌（ACQ）激发三重态3ACQ*的淬灭反应。光解ACQ/EG体系,观察到苊醌中性自由基ACQH•和乙二醇烷基自由基的发射/吸收+发射（E/A+E）的CIDEP信号,ACQH•和CH2(OH)C•HOH由3ACQ*从EG上夺氢生成。光解ACQ/TEMPO/EG体系,3ACQ*与TEMPO相互作用将极化转移给TEMPO。光解ACQ/VC/EG体系,3ACQ*除了从EG上夺氢外,还从VC上夺氢生成VC负离子基As•-。较强的As•-的CIDEP信号表明VC对3ACQ*有明显的淬灭作用。     

吩噻嗪-1,4萘醌-乙二醇体系光化学过程的时间分辨ESR研究

用时间分辨ESR方法研究了吩噻嗪(PTH)-1,4-萘醌(NQ)-乙二醇(RH)体系中的光化学过程.只观察到萘醌的中性半醌自由基NQH^*的全发射极化的CIDEP(化学诱导动态极化)信号,并未观察到极化的萘醌负离子NQ·^-*的CIDEP信号,表明RH与三重态NQ间的质子转移反应远比PTH与NQ间的电子转移反应为快.NQH·^*的CIDEP信号随pH值的变化表明体系中同时有极化自由基NQH·^*与NQH·₂^+*存在,并且其间有质子交换.     

CIDEP in radical-singlet molecular oxygen system

Net absorptive CIDEP generation has been demonstrated on singlet molecular oxygen and 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyl (OTEMPO) radical system in benzene. CIDEP generation was reasonably explained in terms of the radical-triplet pair mechanism of triplet molecular oxygen-OTEMPO pair with doublet precursor. Several excited molecule-OTEMPO systems have been investigated if this CIDEP generation contributes to their CIDEP spectra. Surprisingly strong CIDEP was produced even in the presence of trace amount of dissolved oxygen, which suggests the importance of complete degassing for CIDEP studies in general systems.     

铷蒸气Λ-型系统中的受激Raman谱与光泵效应

从理论和实验上研究了⁸⁵Rb 原子蒸气D1线系统中的受激Raman现象. 在Λ-型能级系统中, 抽运光对弱探测光的影响有两部分: 受激Raman激发和光泵效应. 在一定的抽运光强度和失谐量条件下, 受激Raman谱表现为增益谱或损耗谱; 以光泵效应导致的吸收谱为背景时, 便分别形成了窄线宽透明窗口或线宽差异很大的吸收双线. 理论模拟和实验结果基本符合. 基于这些研究, 从新的角度阐述了在Λ-型系统中的电磁感应透明和Autler-Townes分裂这两个重要现象与受激Raman谱之间的关系. 关键词： 受激Raman谱 光泵效应 电磁感应透明 吸收双线     

CIDEP Created by the Quenching of Photo-Excited Tryptophan at Protein Surface: A Challenge to CIDEP Probing of Protein Structural Changes

Quenching of the triplet excited state of molecular tryptophan by nitroxide radical in 1,4-dioxane and water solutions was investigated by means of time-resolved electron paramagnetic resonance (EPR) and Fourier-transform (FT)-EPR. The chemically induced dynamic electron polarization (CIDEP) signals with net emissive phase were recorded at these quenching events and were analyzed through radical-triplet pair mechanism. The CIDEP time profiles were well reproduced by Bloch and kinetic equations, assuming radical-triplet pair mechanism with the appropriate quenching rate constants. From a comparison of the simulation and the experiment, CIDEP enhancement factor in 1,4-dioxane was determined to be −30 × P _eq, where P _eq is the spin polarization of nitroxide at thermal equilibrium. Net emissive CIDEP was also observed by FT-EPR measurements on the nitroxide quenching of the triplet excited state of tryptophan residue in α-lactalbumin. Magnitude of CIDEP created in α-lactalbumin/nitroxide system depends on the pH condition of α-lactalbumin solution, which is related to protein folding dynamics. We argue the CIDEP mechanism at the α-lactalbumin surface and propose a possibility of a novel CIDEP method to probe a protein surface and structural changes.     

国内CIDEP研究进展

化学诱导动态电子极化（CIDEP）是检测瞬态顺磁粒子并表征其特征的强有力的手段,对于研究光化学和光物理瞬态过程的微观机理和规律有重要意义. 本文较为详细地总结了4种常见的CIDEP机理,讨论了各种极化谱及相应的极化条件;简要介绍了国内研究小组在CIDEP理论以及在均相溶液和微复相体系中光化学过程的CIDEP研究成果.      

Dynamic electron polarization created by the radical-triplet pair mechanism: Application to the studies on excited state deactivation processes by free radicals

The radical-triplet pair mechanism for chemically induced dynamic electron polarization (CIDEP) created in the quenching of excited state molecules by free radicals is explained on the basis of recent time-resolved electron spin resonance spectroscopic results and theoretical studies. The CIDEP of 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) and galvinoxyl radicals exhibit various CIDEP patterns of net and mutliplet types and CIDEP phases of absorption and emission. The CIDEP patterns are described by the quartet-doublet state mixings within the radical-triplet encounter pairs. The mixings by the spin-dipolar and the hyperfine interactions are responsible for the net and the multiplet patterns, respectively. The factors controlling the CIDEP phases are the spin multiplicity of the excited state quenched by radicals and the sign of the intermolecular exchange interaction of the radical-triplet encounter pairs. In particular, the intermolecular charge transfer effect on the exchange interaction is discussed much in detail from the viewpoints of CIDEP magnitudes and phases. A CIDEP creation in the O₂(¹Δ_g)-TEMPO system is also introduced and is described by the radical-triplet pair mechanisms. Applications of this CIDEP used as a probe of O₂(¹Δ_g) in condensed phase are mentioned.     

Photo-Induced Electron Transfer in P3DDT, P3OT, M3EH-PPV Conjugated Polymers Blended with Maleic Anhydride in THF Solution Under UV Flash Photolysis Studied by Means of CW TR ESR

Free-radical signals of positive polarons in conjugated polymer chains and maleic anhydride (MA) anion radicals were registered in poly(3-octylthiophene) P3OT:MA and (poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)?C(1,4-phenylene-1,2-ethenylene)]) M3EH-PPV:MA blends in tetrahydrofuran (THF) solutions under ultraviolet flash photolysis (308?nm) by continuous-wave time-resolved electron spin resonance. Their emissive chemically induced dynamic electron polarization (CIDEP) originated mainly from excited triplet states (triplet mechanism of CIDEP) and partly by from the radical pair mechanism due to the singlet?Ctriplet mixing states. The observed M3EH-PPV polaron spectrum (g ₀?=?2.0029) supports the supposition that the previously registered CIDEP spectra in P3DDT:MA blends (g ₀?=?2.0021) can be attributed to the polaron signals instead of the possible solvate electron signal one.     

Multiplet-to-net CIDEP conversion by MW-pulses with adiabatically ramped amplitude

ABSTRACT

A method is proposed to manipulate electron spin order of spin-correlated radical pairs. As radical pairs are often born in a well-defined spin state, e.g. in the singlet state, they acquire Chemically Induced Dynamic Electron Polarisation (CIDEP). In the case of singlet-state preparation CIDEP is of the multiplet (or anti-phase) type resulting in reduction of EPR (electron paramagnetic resonance) signals due to overlap of absorptive and emissive lines in the spectrum. Here we propose to convert the singlet spin order into net magnetisation of the radical pair by applying a microwave field, with its amplitude slowly (adiabatically) reduced to zero. We demonstrate that by properly choosing the microwave frequency one can completely convert the singlet order into net polarisation of the radical pair with significant enhancement of the signal as compared to multiplet CIDEP. Calculations show that the technique is operative for both weakly coupled and strongly coupled spin pairs. Potential applications of the method are discussed.