Time-resolved powder diffraction study of (4π+4π) photodimerization of anthracene derivatives 時間分解X線粉末回折法によるアントラセン誘導体の(4π+4π)光異性化反応の研究
Time-resolved powder diffraction study of (4π+4π) photodimerization of anthracene derivatives
Ahmed Farghaly Mabied Farghaly
アハマド ファーガリー マービット ファーガリー
Anthracene derivatives are considered as typical examples of photoreactive molecule, which exhibit (4π+4π) photodimerization reaction upon illumination with light of wavelength greater than 300 nm to form dimer phase, and dissociate into its initial monomers thermally or by the illumination of light of wavelength less than 300 nm. Based on their photodimerization properties, many applications were developed, such as fabrication of photo-switchable devices, biological reactions controlling and optical storage memory devices.In order to reveal the reaction kinetics and mechanism of the photodimerization reaction, time-resolved powder diffraction study of anthracene derivatives, 1-chloroanthracene (1-chA) and 9-methylanthracene (9-MA), in the course of solid state (4π+4π) photodimerization reaction was performed. The study was carried out in-situ using synchrotron X-ray source. To analyze the significant information of the collected data, Rietveld refinement was applied. The results of traditional sequential Rietveld refinement showed that the evolution of the dimerization process can be analyzed based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The parameters of the JMAK equation were obtained successfully by Rietveld refinement and suggested that the reaction follows heterogeneous nucleation and one-dimensional growth with a decreasing nucleation rate. Time-dependent diffraction data of 9-MA monomer and dimer phases were analyzed based on the averaged structure in each phase. The monomer molecules have two important movements during the reaction, in which the adjacent reactant molecules shifted relatively each other and at the same time rotate mutually until reaching the distance and angles of conforming the dimer phase. In the dimer phase, the changes of the lattice constants indicate that the molecular arrangement of dimer phase was affected by the movement of monomer molecules and have movements during the dimerization. To see the effect of dimerization process on the molecular arrangement of dimer molecules, two different distances between the adjacent dimer molecules were measured in the time course. The measured distance of C5-C5i decrease with the time progress while the distance of C15-C8 mutually increase giving similar behavior of the mutual rotation of angle 1 and angle 2 of the adjacent monomer molecules. The results were supported by IR and UV-Vis spectroscopic measurements.In conclusion, it is clearly demonstrated that time-resolved powder diffraction is a powerful tool to reveal the kinetics and mechanism of the photodimerization of anthracene derivatives in the course of in-situ solid state (4π+4π) photodimerization reaction.