Inner proton transfer between two trans isomers (tautomerization) in porphyrins plays a crucial role in many biological systems as well as molecular nanotechnology. Although the stepwise mechanism of tautomerization is well accepted, the involved intermediate cis-isomer has not been directly detected owing to its short lifetime and the extremely low intensities of corresponding hydrogen vibrations. Here, taking a single porphine as the prototype, we theoretically demonstrate that Raman intensities of the hydrogen vibrations become accessible under the highly localized plasmonic field because of the symmetry breaking effect. In addition, with the ultrafast incident excitations, we find that Raman signals of cis-porphine could be distinguished from the stable trans isomer, suggesting a general protocol for the direct characterization of transient isomers. Moreover, calculated results reveal that the position of inner hydrogen/deuterium can be unambiguously visualized from Raman images of the corresponding stretching modes, providing a unique optical means for the chemical monitoring of tautomerization in porphine and its derivatives.
[1]Shandong Normal Univ, Shandong Prov Key Lab Med Phys & Image Proc Techn, Sch Phys & Elect, Jinan 250014, Shandong, Peoples R China;
[2]KTH Royal Inst Technol, Dept Theoret Chem & Biol, Sch Engn Sci Chem Biotechnol & Hlth, S-10691 Stockholm, Sweden;
[3]Fudan Univ, Collaborat Innovat Ctr Chem Energy Mat, Shanghai Key Lab Mol Catalysis & Innovat Mat, MOE Key Lab Computat Phys Sci,Dept Chem, Shanghai 200433, Peoples R China;
[4]Univ Sci & Technol China, Hefei Natl Lab Phys Sci, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei 230026, Anhui, Peoples R China
(8.0+极速模式)