Studies On Ultrafast Charge Transfer Of The Photosensitive Processes In Pharmaceutical Molecules

One of the important work of modern scientific research,is to study the physical and chemical processes in molecular scale.With the development of the femtosecond laser pulse,the resolution ratio of time scale in these studies goes into femtosecond.On this basis,the physical processes in atom molecule scale,such as intramolecular conversion,intersystem crossing,proton transfer,electron transfer,charge transfer,resonance energy transfer,vibration relaxation,fluorescence,phosphorescence,stimulated radiation,etc,are investigated.The charge transfer process is familiar in biological system,such as photosynthsis,photolyase,photochrome,DNA damage and so on.In these systems,the charge transfer process act as the electronic transfer and energy transfer channel between molecules.The high energy electron of the excited photosensitive molecule transfer to the steady state molecule around and keep it in the excited state,which may lead to other ultrafast dynamics in the follow.The intramolecular charge transfer process of the excited photosensitive molecule may be the precondition of the intennolecular charge transfer processes.Charge transfer is one of the photosensitive processes,which are represent by the special effects of the medicine users after irradiation by UV-A or UV-B photosource,for phamaceutical molecules.If the special effects are good for the illness it could be called photodynamics therapy which may kill the targeted cells,but if the effects are harmful to human,it may be the phototoxicity which need to avoid if possible.The mechanisms of of photosensitive processes for phamaceutical molecules have been founded are the charge transfer and the exist of triplet state.The charge transfer may promote the reactions between the photoreceptor and the around,which may have special effect to human.The triplet state may activate the O2 in human which could oxidated the DNA or protein.The ultrafast dynamic study on photosensitive processes of phamaceutical molecules may obtain the mechanism on photophysics and analyse the function of each group,which could be used for perfecting the form of phamaceutical molecules by increasing helpful group and decreasing harmful group.In this work,the ultrafast charge transfer of 9-anthraldehyde,ofloxacin and 1-aminoanthraquinone are studied by femtosecond transient absorption spectroscopy.Ofloxacin is a kind of photosensitive drug which is on sell,and the study on the charge transfer of it could help us to analyse the mechanism of photosensitive processes.9-anthraldehyde and 1-aminoanthraquinone are medical intermediate and photoreceiver,a part of drugs based on them are photosensitiveness and phototoxicity.The study on charge transfer of them could give us more information for the research and development of drugs.This thesis mainly consists of three parts:The first part is about the photoinduced intramolecular charge transfer(CT)of 9-anthraldehyde in ethanol and hexane solvents studied by femtosecond transient absorption spectrum combined with quantum chemical calculations.The 9-anthraldehyde is excited by 400 nm and through a CT process to the S1 state.The CT was observed within 0.11 ps in ethanol and 0.23 ps in hexane.Due to the stronger polarity of ethanol,the CT is faster than in hexane.The following ISC is determined to be 22.3 ps and 21.4 ps in two solvents,respectively.However,the timescales of ISC are similar in both solvents since the excited energies of the S)and triplet states are close to each other.The exists of the fast CT and ISC processes which may induced the damage of DNA and protein suggest that the photosensitiveness and phototoxicity are considerable for the medicine based on 9-anthraldehyde.In the second part,the mechanism of intrarmolecular CT and the following radiationless dynamics of ofloxacin phannaceutical product were investigated using femtosecond absorption spectroscopy combined with quantum chemical calculations.The CT and the intersystem crossing(ISC)processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiation of the excited S1 state.The CT occurs within a time constant of?1.4 ps.The following ISC is determined to be?158 ps and quantum yield of ISC can be measured to keep?0.33.This work provides bases and reference for the research of the mechanism of the phototoxicity of ofloxacin.The third part is about the ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product using femtosecond absorption spectroscopy combined with quantum chemical calculations.Following photoexcitation with 460 nm,the 1-aminoanthraquinone transfer of a twisted intra-molecular charge transfer(TICT)process to the S1 state with timeconstant of 5 ps.The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps.Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutical products,and may contribute to more studies on the machenism and development of anthraquinones.