In-situ Raman Spectroscopy Srudy On Laser Induced[2+2]Cycloaddition And Cleavage Reactions

Electrochemical redox treatment with irreversible cyclic voltammetry curves is necessary for 4-vinylpyridine(4-VP) or pyridyl substituted olefin [2+2] cycloaddition on electrode(SERS substrate). Hypotheses are given as follows, during the electrochemical redox process, Ag~+diffused from silver electrode is captured with 4-VP or pyridyl substituted olefin in electrolytes, and the resulted Ag~+complexes deposits on the electrode(SERS substrate) surface, which acts as laser photochemistry materials. Laser as heat source induces [2+2] cycloaddition, where Ag~+controls the parallel C=C double bond within 4.2 ?to satisfy the [2+2] stereochemistry.Crystal 1([Ag2(4-VP)4][TFA]2) & Crystal 2([Ag2(PEA)4][TFA]2) are synthesized with 4-VP, Ethyl-(pyridine-4-yl)prop-2-enotate(PEA) and silver trifluoroacetate(Ag TFA), via crystal engineering method. X-ray single crystal diffraction results indicate that the ligands(4-VP, PEA) parallel C=C distance falls in 4.2 ?. During [2+2] cycloaddition reaction process, Py-Cyclobutane C-C vibrations at 845 cm-1& cyclobutane skeletal C-C at 1145 cm-1increase, while C=C at 1635 cm-1decreases. Laser induced [2+2] cycloaddition are power- and wavelength-dependent. In one-step method, Crystal 1/Crystal 2complexes deposit on Ag nanostructures(Ag NSs) polyaniline(PANI) composite film.[2+2] cycloaddition are confirmed with 845 cm-1& 1145 cm-1, furthermore, laser-melted holes are confirmed with SEM/optical images. Laser induced [2+2] cycloaddition sheds new light on electrode(SERS substrate) photochemistry and natural products synthesis in gram/kilogram scale. Both melting point(no more than 200?C, carbonization temperature no more than 300?C) and stereochemistry(C=C with moving freedom terminal groups COOEt/H) could be seen as [2+2] cycloaddition criteria. On the contrary, Crystal 3([BPE]2[RES]2) & Crystal 4([BPEP]2[RES]2) with rigid structure and higher melting points(225?C, 211?C) are photochemistry inactive.Diethyl-3,4-di(pyridin-4-yl)cyclobutane-1,2-dicarboxylate(DCCB) coordinated with Ag TFA gives Crystal 5([Ag3(DCCB)][TFA]3). X-ray single crystal diffraction results indicate two-dimensional(2 D) structures packed into Crystal 5 in space. Two pyridyl groups of DCCB coordinated with silver ions(labelled as Ag1), two carboxyl coordinated with Ag~+(labelled as Ag2). Three TFA, two Ag1, one Ag2, one central Ag~+give a tetrahedron configuration, which connected with DCCB head and tail forming one-dimensional(1 D) chains. 1 D chains link with each other to give a 2 D structure. Full power 633 nm laser(3 m W) drives Crystal 5 cleavage reaction, proved with characteristic C=C peak at1635 cm-1, while DCCB is laser photochemistry inactive. So heavier Ag~+thermal movement is necessary for cleavage. 1372 cm-1& 1429 cm-1indicate strained cyclobutane.Power-dependent is proved with the fact that there is no C=C vibration peak under 50%power(1.57 m W). It comes to the conclusion that heat effects driven Ag~+movement conquers cyclobutane bond energy. On DSC curve, 177-200?C exothermic peak is assigned to Crystal 5 melting process. Raman spectra confirms Crystal 5 cleavage treated with200?C, while just carbon treated with 300?C. Estimated temperature is 300?C for 100%(3 m W), and no more than 170?C for 50%(1.57 m W), at which temperature Ag~+slow movement cannot conquer the cyclobutane bond energy.With huge specific area & surface energy, noble metallic(Ag/Au) nanoparticles(NPs) catalyze TPCB/Dimethyl-3,4-di(pyridin-4-yl)cyclobutane-1,2-dicarboxylate(DMCB) cleavage reaction through coordination bands. TPCB/DMCB developed on thin layer chromatography(TLC) plate is sprayed with Ag sol, SERS spectra confirm cleavage products BPE/PMA. TLC improves repeatability of cleavage reaction for it overcomes the crystallization issue on Ag/Au NPs’ surface. In-situ time-dependent SERS spectra confirm the instant cleavage, coordination bonds between noble metallic NPs and pyridyl groups accounts for this phenomenon. It is easier for TPCB than DMCB to undergo cleavage reaction. The reason is the weak interaction between silicon sol and pyridyl during TLC development process. For TPCB, there are two pyridyl left to coordinate with Ag/Au NPs, even if two interacted with silicon sol. However, for DMCB, there would be less chances to interact with Ag/Au NPs. Noble metallic NPs catalyzed cleavage reaction cast new light on nano-medicine and DNA repair.