Mono-, bi- quinolinium branches carbazole as groove binding mode of two-photon excited fluorescent probe interacting with DNA and nucleus imaging

Abstract

In this paper, new two-photon fluorescent nucleic acid probes, 3-(N-methyl -2- vinyl quinolinium iodide)-9-ethylcarbazole (M2EQC) and 3,6-di-(N-methyl -2- vinyl quinolinium iodide)-9-ethylcarbazole (DM2EQC), have been designed and synthesized. The two compounds are fluorescent DNA probes with long wavelength emission (670 and 650 nm, respectively) irradiated by near-infrared light. The new probes exhibit an obvious improvement in the two-photon absorption action cross-section (222.68 GM and 290.72 GM, respectively). They show the same nuclear localization level as Hoechst 33342 when staining 3T3 cells together. The bioluminescence imaging effect of the compound’s stained cells excited by the 800 nm laser was better than that at 400 nm. The probes also show three-dimensional imaging capability of a single nucleus and lower cytotoxicity, besides the lower fluorescence bleaching effect and higher optical stability than the reported two-photon nucleic acid probe. The fluorescence decay rate was 0.023%/min and 0.020%/min, respectively. The quantum chemical calculation results reveal the reason for spectra changing and we speculate the mechanism of the probes binding with DNA.