Bizimana Laurie A, Epstein Jordan, Brazard Johanna, Turner Daniel B
Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
J Phys Chem B. 2017 Mar 30;121(12):2622-2630. doi: 10.1021/acs.jpcb.7b02180. Epub 2017 Mar 16.
Numerous time-resolved studies of the P to P photoisomerization in phytochrome Cph1 have revealed multiphasic excited-state decay kinetics. It remains unclear whether these kinetics arise from multiple ground-state conformational subpopulations or from a single ground-state conformation that undergoes an excited-state photoisomerization process-either branching on the excited state or relaxing through multiple sequential intermediates. Many studies have attempted to resolve this debate by fitting the measured dynamics to proposed kinetic models, arriving at different conclusions. Here we probe spectral signatures of ground-state heterogeneity of P. Two-dimensional electronic spectra display negligible inhomogeneous line broadening, and vibrational coherence spectra extracted from transient absorption measurements do not contain nodes and phase shifts at the fluorescence maximum. These spectroscopic results support the homogeneous model, in which the primary photochemical transformation of P to Lumi-R occurs adiabatically on the excited-state potential energy surface.
对植物光敏色素Cph1中P到P光异构化的大量时间分辨研究揭示了多相激发态衰减动力学。目前尚不清楚这些动力学是源于多个基态构象亚群，还是源于经历激发态光异构化过程的单一基态构象——要么在激发态上分支，要么通过多个连续中间体弛豫。许多研究试图通过将测量的动力学拟合到提出的动力学模型来解决这一争论，但得出了不同的结论。在这里，我们探测P基态非均质性的光谱特征。二维电子光谱显示出可忽略不计的非均匀线宽展宽，并且从瞬态吸收测量中提取的振动相干光谱在荧光最大值处不包含节点和相移。这些光谱结果支持均匀模型，其中P到Lumi-R的初级光化学转化在激发态势能面上绝热发生。
