Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Faraday Discuss. 2013;163:159-71; discussion 243-75. doi: 10.1039/c3fd20149j.
The excited and ground state dynamics of a series of 1,3-cyclohexadiene derivatives and their hexatriene photoproducts are studied using ultrafast broadband UV-visible transient absorption spectroscopy. The substitution pattern around the cyclohexadiene backbone alters the excited state potential energy surface in the Franck-Condon region as evidenced by changes in the excited state absorption and fluorescence properties of the systems. Unsubstituted 1,3-cyclohexadiene and alpha-phellandrene exhibit no excited state absorption while a strong excited state absorption in the visible spectral region is observed for both alpha-terpinene and Provitamin D3. Steric factors introduced by the ring substitutions determine the dominant rotational isomer at equilibrium for the hexatriene photoproducts. Coupling to the solvent during the conformational relaxation from the initial helical all-cis hexatriene is unique to each photoproduct, but the relaxation process occurs on a 6-10 ps timescale regardless of the size or substitution pattern on the triene.
使用超快宽带紫外可见瞬态吸收光谱研究了一系列 1,3-环己二烯衍生物及其六烯光产物的激发态和基态动力学。环己二烯主链周围的取代模式改变了 Franck-Condon 区域中的激发态势能表面，这可以通过系统的激发态吸收和荧光性质的变化来证明。未取代的 1,3-环己二烯和α-蒎烯没有激发态吸收，而α-松油烯和维生素 D3 前体都在可见光谱区域观察到强的激发态吸收。环取代引入的空间位阻因素决定了六烯光产物在平衡时的主要旋转异构体。从初始螺旋全顺六烯到构象弛豫期间与溶剂的耦合对于每个光产物都是独特的，但无论三烯的大小或取代模式如何，弛豫过程都发生在 6-10 ps 的时间尺度上。
