State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, PR China.
Phys Chem Chem Phys. 2012 Oct 21;14(39):13702-8. doi: 10.1039/c2cp42122d.
Symmetrical and unsymmetrical cyanine dyes are used in different applications due to their different fluorogenic behaviors toward bio-macromolecules and micro-environments. In the present paper, computational studies on these dyes reveal that the potential energy of the electronic excited state is controlled by C-C bond rotational motion, which causes mainly nonradiative deactivation, according to the activation energies for the rotation. The rotations of different C-C bonds in the molecules have quite different rotational activation energies. Symmetrical dyes (Cy) possess an obviously higher rotating energy barrier as well as a larger energy gap compared to unsymmetrical dyes (TO). The C-C bond rotation close to the quinoline moiety of unsymmetrical thiazole orange (TO) allows the dye to possess the lowest energy barrier and also the lowest energy gap. This rotation plays a major role in reducing fluorescence quantum yields and providing a low fluorescent background in the free states of the unsymmetrical cyanine dyes. The results might provide a foundation for the interpretation of the behavior of the dyes and are useful for the future design of new cyanine fluorophores.
对称和非对称的菁染料由于其对生物大分子和微环境的不同荧光行为而应用于不同的领域。在本文中，通过计算研究这些染料发现，电子激发态的势能是由 C-C 键旋转运动控制的，根据旋转的活化能，这主要导致非辐射失活。分子中不同 C-C 键的旋转具有非常不同的旋转活化能。与非对称染料（TO）相比，对称染料（Cy）具有明显更高的旋转能垒和更大的能隙。非对称噻唑橙（TO）靠近喹啉部分的 C-C 键旋转使得染料具有最低的能垒和能隙。这种旋转在降低荧光量子产率和提供非对称菁染料自由态的低荧光背景方面起着主要作用。这些结果可能为染料行为的解释提供了基础，并有助于未来设计新的菁类荧光团。
