A bis‐triarylborane tetracation (4‐Ar₂B‐3,5‐Me₂C₆H₂)‐C≡C−C≡C‐(3,5‐Me₂C₆H₂‐4‐BAr₂ [Ar=(2,6‐Me₂‐4‐NMe₃‐C₆H₂)⁺] (2⁴⁺) shows distinctly different behaviour in its fluorimetric response than that of our recently published bis‐triarylborane 5‐(4‐Ar₂B‐3,5‐Me₂C₆H₂)‐2,2′‐(C₄H₂S)₂–5′‐(3,5‐Me₂C₆H₂‐4‐BAr₂) (3⁴⁺). Single‐crystal X‐ray diffraction data on the neutral bis‐triarylborane precursor 2 N confirm its rod‐like dumbbell structure, which is shown to be important for DNA/RNA targeting and also for BSA protein binding. Fluorimetric titrations with DNA/RNA/BSA revealed the very strong affinity of 2⁴⁺ and indicated the importance of the properties of the linker connecting the two triarylboranes. Using the butadiyne rather than a bithiophene linker resulted in an opposite emission effect (quenching vs. enhancement), and 2⁴⁺ bound to BSA 100 times stronger than 3⁴⁺. Moreover, 2⁴⁺ interacted strongly with ss‐RNA, and circular dichroism (CD) results suggest ss‐RNA chain‐wrapping around the rod‐like bis‐triarylborane dumbbell structure like a thread around a spindle, a very unusual mode of binding of ss‐RNA with small molecules. Furthermore, 2⁴⁺ yielded strong Raman/SERS signals, allowing DNA or protein detection at ca. 10 nm concentrations. The above observations, combined with low cytotoxicity, efficient human cell uptake and organelle‐selective accumulation make such compounds intriguing novel lead structures for bio‐oriented, dual fluorescence/Raman‐based applications.

Flexibility, an intriguing yet far from being a commonly observed property of single crystals, is highly sought after as it enables crystal application in innovative technologies. Here, we report on anisotropically elastic single crystals of two novel 1D coordination polymers (CPs) featuring bridging halides (Cl (1); Br (2)) and pyrazinamide ligands that enabled the determination of the bending mechanism and exploration of their mechanical properties. The mechanism identified distinctly differs from the mechanisms of elastically flexible molecular crystals subjected to mechanical stress and 1D plastically deformable crystals under quasi-hydrostatic pressure, the mechanisms of reconfigurable crystals uncovered thus far. By mapping the structural modification across the bent crystal 1 using microfocus synchrotron radiation, we found that both the 1D structural spine (controlling the distance between the organic ligands) and the ligands themselves adapt to the changes in external conditions. While the spine expands through the modifications of the bridging angles, causing a consequent enlargement of the metal···metal distances as going from the interior to the exterior of the bend, the ligands rotate toward linearity with the bending face. In addition, the extent of changes along the two other crystal axes is brought into a connection with the relative energies of the weakest links and crystal stiffness in those directions.

Surface-enhanced Raman scattering (SERS) enhancement factors (EF) were evaluated for RNA mononucleotides: adenosine 5\u27-monophosphate (AMP), guanosine 5\u27-monophosphate (GMP), cytidine 5\u27-monophosphate (CMP) and uridine 5\u27-monophosphate (UMP), on silver nanoparticles, which differed in shape (nanospheres, nanostars) and stabilizing anionic layer (chlorides, citrates) on the metal surface. In freshly prepared silver colloids the enhanced Raman scattering was observed for all the RNA mononucleotides on the chloride coated silver nanospheres, Ag_Cl nsp (EF ≈ 104), for AMP only on the citrate coated silver nanospheres, Ag_cit nsp (EF ≈ 103), while not obtained at all for any of the mononucleotides on the citrate stabilized silver nanostars, Ag_cit nst. Upon aggregation, the SERS activity of all the silver colloids increased, whereby the purine mononucleotides, AMP and GMP, more strongly scattered radiation on Ag_Cl nsp, and the pyrimidine mononucleotides, CMP and UMP, on Ag_cit nsp. Regardless of the silver nanoparticles, the higher EFs were evaluated for AMP and GMP (EF up to 5 × 106), than for CMP and UMP (EF ≈ 5 × 104)