Simultaneous binding of a cyclophane and classical intercalators to DNA: observation of FRET-mediated white light emission

Abstract

DNA-assisted Forster resonance energy transfer (FRET) between an anthracene-based cyclophane (CP) and mono-and bis-intercalators such as propidium iodide ( PI) and ethidium homodimer-1 (EHD), respectively, has been studied using various photophysical and biophysical techniques. The cyclophane and PI exhibited simultaneous binding to DNA at all concentrations studied and showed DNA-assisted FRET from the excimer of cyclophane with a FRET efficiency of ca. 71%. On the other hand, the bis-intercalator EHD, only at lower concentrations (<3 mu M), can act as an acceptor for the energy transfer process with a lower efficiency of ca. 44%. At higher concentrations (>15 mu M), EHD, on account of its higher binding affinity, displaces cyclophane from the DNA scaffold. Employing the ternary system comprising of the cyclophane, DNA and PI and fine-tuning the concentrations of the components in a molar ratio of 1 : 0.75 : 0.05 (CP: DNA: PI) we have demonstrated white light emission with CIE coordinates (0.35, 0.37).