The Effects Of PH Valueon Ultrafast Dynamics Of Porphyrin

As we all know, the development of ultrashort pulse has been achieved the laserpulse output in femtosecond magnitude. Today, femtosecond has become animportant tool for the majority of scholars to research the transient dynamic processesof material. Researchers are not satisfied to know materials’ simple transition process,and they are eager to understand the transient relaxation process of the materials. Bythe help of femtosecond lasers this target can be achieved with its characteristics ofhigh time resolution and high transient power. At present, because various materialshave been synthetized continually, so the research of material’s ultrafast dynamics hasa very broad space for development. Through the measurement of material’s ultrafastdynamics process, Scholars have gotten the information of femtosecond time scalecorresponding to the excited state vibrational relaxation, internal conversion andintersystem crossing processes of materials. In addition, more and more types ofsubstance is gradually researched. From inorganic materials, semiconductor materialssuch as Zinc Oxide, Cadmium Sulfide to the organic polymer light-emitting material,and then to the cross-border life class of material, promote the detection of materialby femtosecond laser step by step, and broaden the field of study, meanwhile makepeople realized that each substance has its own special internal electron transferprocess clearly. Now, the femtosecond laser has been widely used in the ultrafastdynamics of the physical, chemical and biological interdisciplinary research.Since the last decade, the study of life materials like porphyrins has aroused theinterest of many scholars. Due to the special structure of porphyrin compounds in thenature of the organism life activities occupies a very important position, andporphyrin and its derivatives have a wide application, e.g. hematoporphyrin bear thetask of oxygen and carbon dioxide transport in human respiration. In PhotodynamicTherapy, porphyrin compounds can achieve the purpose of the treatment of cancer asphotosensitizer. In study of molecular devices, Metallic porphyrin can work as thelight energy converter, optoelectronic gate and organic solar cells, etc. The material that we studied is protoporphyrin and iron porphyrin, a kind of lifematerials. Because porphyrin compounds plays a vital role in our body, so it isnecessary to conduct a comprehensive analysis of porphyrin to understand itsstructural characteristics, mechanism and influencing factors. Firstly, we hope to getthe information of electronic transfer process from porphyrin’s excited states back toground state, through the transient dynamics research. Figure out the intrinsicprinciples of these two porphyrins played in our body. Secondly, change the pH valueof the two solutions, and research the influence of pH on the electron transfer andenergy transfer of porphyrin. Because the pH value in our body of blood is changingall the time, so when we take porphyrin drugs, different pH values will affectporphyrin structure and electronic and energy transfer process, which can affect theefficacy in our body. So clear up the inner essence of electron transfer and energytransfer in porphyrin, is equivalent to study the mechanism of the efficacy of the drugin the body. It is very meaningful for the treatment of neoplastic diseases and thedevelopment of new drugs. Therefore, we study two kinds of porphyrins’ UV-visabsorption spectra, fluorescence spectra, ultrafast dynamics process, and obtainedsome conclusions and laws.1. UV-vis absorption spectrum. Through this experiment, we found that in thesolution of pH≥7, porphyrin UV-vis absorption spectra can be considered thatbasically no changes, but in the solution of pH <7, the spectrum is significantlyredshift. Because while add H₂SO₄into the solution, protonation leads to energy levelspacingâ–³E of protoporphyrin excited state and ground state decreases.2. Fluorescence spectrum.The experimental results show that the protoporphyrinalways has the fluorescence emission while iron porphyrin doesn’t emit fluorescence.We analyzed their ultrafast process and got the explanation that why the two differentrelaxation processes occur. Protoporphyrin’s relaxation processes isS₂→S₁→S₀while the iron porphyrin’s relaxation processes isS₂→（S₁）→LMCT→S₀.Therefore, the iron porphyrin doesn’t have fluorescence, and have no relationshipwith the pH value. But in the protoporphyrin solution of pH <7, protoporphyrin’s fluorescence will occur blueshift due to thea2ushift to a higer orbital.3. Ultrafast Dynamics: Through the measurement of ultrafast dynamics spectral, wehave analyzed the two kinds of porphyrin’s electronic and energy transfer in ultrafastprocess detailedly. The study found that the H₂SO₄solution of pH <7has moreobvious influence on the two porphyrin. Add H₂SO₄into the solution, the protonationlead to the changes of protoporphyrin molecule structure, and thus produce changes inthe level spacing, and ultimately lead to different pH values corresponding to differentrelaxation time. The addition of H₂SO₄to the influence of iron porphyrins appears thesame regularity, with the decrease of pH value the reduction will occur in therelaxation time of excited states. The reason is H+gathered in the center of the ironporphyrins and reduced the core size, thus decreased the HOMO and LUMO levelspacing, finally shorten the electronic transition time. Yet, we still have to analyzewhy iron porphyrin doesn’t show evidence signal in the solution of NaOH in thefurther.