Stacked Thiazole Orange Dyes in DNA Capable of Switching Emissive Behavior in Response to Structural Transitions

Functional nucleic acids with the capability of generating fluorescence in response to hybridization events, microenvironment or structural changes are valuable as structural probes and chemical sensors. We now demonstrate the enzyme‐assisted preparation of nucleic acids possessing multiple thiazole orange (TO) dyes and their fluorescent behavior, that show a spectral change from the typical monomer emission to the excimer‐type red‐shifted emission. We found that the fluorescent response and emission wavelength of the TO dyes were dependent on both the state of the DNA structure (single‐ or double‐stranded DNA) and the arrangement of the TO dyes. We showed that the fluorescent behavior of the TO dyes can be applied for the detection of RNA molecules, suggesting that our approach for preparing the fluorescent nucleic acids functionalized with multiple TO dyes could be useful to design a fluorescence bioimaging and detection technique of biomolecules. Multi‐color fluorescent nucleic acids: Nucleic acids possessing multiple thiazole orange (TO) dyes were synthesized and their fluorescent behavior was investigated. The TO‐conjugated DNA showed a spectral change from the typical monomer emission to the excimer‐type red‐shifted emission, which were dependent upon both the state of the DNA structure (single‐ or double‐stranded DNA) and the arrangement of the TO dyes.