Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 København Ø (Denmark).
Present address: Faculty of Landscape Architecture, Horticulture, and Crop Production Science, Swedish University of Agricultural Sciences, Box 55, 230 53 Alnarp (Sweden).
Chemistry. 2015 Jun 1;21(23):8521-9. doi: 10.1002/chem.201500355. Epub 2015 Apr 27.
At first glance, aminorhodamine (ARh) is a typical pH responsive fluorescent, rhodamine-type dye. However, hidden under the typical rhodamine absorption band, ARh has another electronic transition of similar energy, but polarized orthogonal to that of the rhodamine chromophore. This transition-assigned to an arylpyrylium type chromophore contained in the system-is responsible for the sensor action of the dye. ARh is non-fluorescent, while protonation of a donor amino group turn on a strong rhodamine-type emission. At low temperature in frozen solution emission from both electronic subsystems of ARh are observed. In order to achieve more complete understanding of the photophysical mechanisms in this type of fluorescent probes, ARh and its protonated counterpart HARh were studied by absorption and fluorescence spectroscopy, computational chemistry, and at low temperatures in solid solution. Results from fluorescence anisotropy and time-resolved fluorescence spectra establish a bichromophore model and suggest that a remarkable weak coupling between the two nearly isoenergetic excited states in ARh enables the dual emission. All the complicated properties observed for ARh was accounted for by a bichromophore model describing the electronic system of ARh as a bichromophore constituted by a rhodamine and an arylpyrylium subsystem.
乍一看，氨基罗丹明（ARh）是一种典型的 pH 响应荧光罗丹明型染料。然而，在典型的罗丹明吸收带下，ARh 还有另一个能量相似但极化方向与之正交的电子跃迁。这种跃迁归因于系统中含有的芳基吡喃鎓型发色团，是该染料的传感作用的原因。ARh 本身无荧光，而供体氨基质子化会产生强烈的罗丹明型荧光。在冷冻溶液的低温下，可以观察到 ARh 的两个电子子系统的发射。为了更全面地了解这类荧光探针中的光物理机制，我们通过吸收和荧光光谱、计算化学以及固态溶液中的低温条件对 ARh 及其质子化的对应物 HARh 进行了研究。荧光各向异性和时间分辨荧光光谱的结果建立了双发色团模型，并表明 ARh 中两个几乎等能量的激发态之间存在显著的弱耦合，从而实现了双发射。ARh 所有复杂的性质都可以通过双发色团模型来解释，该模型将 ARh 的电子系统描述为由一个罗丹明和一个芳基吡喃鎓子系统构成的双发色团。
