摘要
There is a pressing need to develop fluorescent dyes with light emission peaks in the wavelength range of 650-950 nm for optical live-cell imaging applications. The advancement of fluorescent dyes with a large Stokes shift is imperative for their biological applications. A novel domino reaction is developed with success for the synthesis of diverse 9aH-benzoquinolizines in 65-95% yields through reaction of alpha-silylaryl triflates, pyridine derivatives, and activated alkynes at room temperature. This single-flask reaction involves completion of a 1,2-elimination, a 1,2-addition, and an intermolecular (4 + 2) cycloaddition in situ. Among 15 new products, diethyl 9aH-tribenzo[c,f,h]quinolizine-1,2-dicarboxylate with extension of pi-conjugation is identified as the top-performing dye. It shows near-infrared fluorescent emission at 674 nm with the Stokes shift of 197 nm, epsilon max = 5.62 x 104 M-1 cm-1, Phi fl = 15.2%, and tau av = 10.1 ns. It also exhibits excellent photostability with only 4.97% decomposed under irradiation with an Hg lamp for 60 min. With a remarkable 96 +/- 2% viability, minimal toxicity toward CT-26 cancer cells, and coupled with promising results from confocal microscopy, this 9aH-tribenzoquinolizine emerges as an ideal fluorescent dye for imaging live cells.