title: The nature of the different environmental sensitivity of symmetrical and unsymmetrical cyanine dyes: an experimental and theoretical study.
abstract: 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.
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, PR China.
authors.forename: Jianfang
authors.initials: J
authors.lastname: Cao
authors.forename: Tong
authors.initials: T
authors.lastname: Wu
authors.forename: Chong
authors.initials: C
authors.lastname: Hu
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
authors.forename: Wen
authors.initials: W
authors.lastname: Sun
authors.forename: Jiangli
authors.initials: J
authors.lastname: Fan
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Peng
mesh_terms: D000818:Animals; D002232:Carbocyanines / Q000737:chemistry*; D002417:Cattle; D004247:DNA / Q000032:analysis; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory; D012399:Rotation; D014783:Viscosity
chemical_list: D002232:Carbocyanines; D005456:Fluorescent Dyes; D004247:DNA; C427203:calf thymus DNA