Pendon Zeus D, Gibson George N, van der Hoef Ineke, Lugtenburg Johan, Frank Harry A
Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT 06269-3060, USA.
J Phys Chem B. 2005 Nov 10;109(44):21172-9. doi: 10.1021/jp0529117.
Steady-state absorption and femtosecond time-resolved optical spectroscopic studies have been carried out on all-trans-beta-carotene, 15,15'-cis-beta-carotene, all-trans-spheroidene, and 13,14-locked-cis-spheroidene. We examine in detail the effect of isomer geometry on the spectroscopic properties and photophysics of the low-lying S(1) (2(1)A(g)(-)) and S(2) (1(1)B(u)(+)) excited states of these molecules. The experiments on 13,14-locked-cis-spheroidene, a molecule incapable of undergoing cis-to-trans isomerization, provide a unique opportunity to examine the role of isomer geometry in controlling excited-state deactivation of carotenoids. The kinetic results have been obtained using both single wavelength transient absorption measurements and global fitting procedures. The overall scheme for the deactivation of these molecules after S(0) --> S(2) photon absorption is decay of S(2) to a vibrationally hot S(1) state, followed by vibrational relaxation within S(1), and finally, S(1) --> S(0) internal conversion back to the ground state. Changes in isomer geometry are shown to lead to small but noticeable alterations in the spectroscopic and kinetic behavior of the molecules. The effects are interpreted in terms of minor alterations in excited-state energy and vibrational coupling upon isomerization that bring about changes in the spectroscopic and kinetic behavior of this biologically important class of pigments.
已对全反式-β-胡萝卜素、15,15'-顺式-β-胡萝卜素、全反式-类球烯和13,14-锁定顺式-类球烯进行了稳态吸收和飞秒时间分辨光谱研究。我们详细研究了异构体几何结构对这些分子低能级S(1)（2(1)A(g)(-)）和S(2)（1(1)B(u)(+)）激发态的光谱性质和光物理过程的影响。对13,14-锁定顺式-类球烯（一种不能进行顺反异构化的分子）的实验，为研究异构体几何结构在控制类胡萝卜素激发态失活中的作用提供了独特的机会。动力学结果是通过单波长瞬态吸收测量和全局拟合程序获得的。这些分子在S(0)→S(2)光子吸收后失活的总体方案是：S(2)衰减到振动热的S(1)态，随后在S(1)内进行振动弛豫，最后，S(1)→S(0)内转换回到基态。结果表明，异构体几何结构的变化会导致分子的光谱和动力学行为发生微小但明显的改变。这些效应可根据异构化时激发态能量和振动耦合的微小变化来解释，这些变化导致了这类具有生物学重要性的色素的光谱和动力学行为的改变。
