Departments of Chemistry & Toxicology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
Chem Commun (Camb). 2019 Mar 19;55(24):3540-3543. doi: 10.1039/c8cc10132a.
The coumarin-hemicyanine hybrid is an internal charge transfer (ICT) dye that features a donor-π-acceptor motif and displays two well-resolved absorption bands at ∼350 nm for the donor coumarin and ∼550 nm for the fully-conjugated dye. Herein, we demonstrate that preferential excitation of the dye at 350 nm, ascribed to a twisted conformation, gives rise to two well-resolved emission bands at ∼450 nm for the coumarin and ∼650 nm for the planar dye that are highly quenched in water. Unexpectedly, the coumarin blue emission was found to 'turn-on' to aprotic and viscous solvents and respond to binding bovine serum albumin (BSA) in aqueous media. In contrast, the red ICT emission was sensitive to protic solvent polarity and responded to binding the G-quadruplex (GQ) DNA structure produced by the heme binding aptamer (PS2.M). Our studies also demonstrate the influence of the alkyl group attached to the dye quaternary nitrogen atom in determining the microenvironment sensitivity and ability to differentiate biopolymer types.
香豆素-半花菁杂合体是一种内电荷转移（ICT）染料，具有给体-π-受体结构，在 ∼350nm 处显示出两个完全分离的吸收带，分别对应于供体香豆素和完全共轭的染料。在此，我们证明了在 350nm 处优先激发染料归因于扭曲构象，导致在 ∼450nm 处香豆素和 ∼650nm 处平面染料的两个完全分离的发射带，这些发射带在水中高度猝灭。出乎意料的是，香豆素蓝发射被发现“打开”到非质子和粘性溶剂中，并响应结合牛血清白蛋白（BSA）在水介质中。相比之下，红色 ICT 发射对质子溶剂极性敏感，并响应与由血红素结合适体（PS2.M）产生的 G-四链体（GQ）DNA 结构的结合。我们的研究还表明，与染料季铵氮原子相连的烷基的影响决定了微环境的敏感性和区分生物聚合物类型的能力。
