Nickel(0)‐Catalyzed [2+2+2] Cycloadditions of Linked Bisdiynes with Diaryl Alkynes Generates D‐π‐A‐π‐D Bis(arylethynyl)indane‐Based Organic Frameworks as Noncytotoxic Probes for Ds‐DNA/Ds‐RNA

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Nickel(0)‐catalyzed [2 + 2 + 2] cycloadditions of linked bisdiynes with diarylacetylenes were performed using the Ni(II) precursor complex [(TMEDA)Ni( o ‐tolyl)Cl] in the presence of PPh 3 ligands to generate the active Ni(0) species. Optimal reactivity was observed when electron‐rich bisdiynes reacted with electron‐deficient diarylacetylenes, affording air‐stable, approximately C 2v ‐symmetric D‐π‐A‐π‐D bis(arylethynyl)indane‐based dyes containing o ‐terphenyl cores. Spectroscopic analyses revealed strong solvatochromic emission with high quantum yields in solution, except for the nonemissive bis‐ N ‐methylpyridinium derivative 4,4 ′ ‐(4,7‐bis((4‐(bis(4‐methoxyphenyl)amino)phenyl)ethynyl)−2,3‐dihydro‐1H‐indene‐5,6‐diyl)bis(1‐methylpyridin‐1‐ium) ditriflate, 10 , pointing toward the decisive impact of pyridine methylation on the nonradiative relaxation of the fluorophore. Vibrational studies of the triarylamine dyes displayed a prominent alkyne stretching band in both Raman and IR spectra, applicable for use as a probe. Biorelevant studies revealed that the synthesized dyes bind strongly to double‐stranded DNA and RNA, most likely through groove insertion, leading to significant fluorescence quenching. Only the dicationic derivative 10 showed a characteristic CD response, attributed to additional electrostatic interactions that orient the dye within the DNA minor or RNA major groove. The dyes had minimal effects on polynucleotide thermal stability, suggesting that hydrophobic and van der Waals forces dominate the binding, except for derivative 10 , which also involves electrostatic interactions. All compounds were found to be nontoxic toward human cell lines, indicating their promise as multimodal fluorescence, CD, and Raman probes for intracellular and extracellular bioimaging applications.

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