Synthesis of Controlled Chain Length Formyl Oligo-p-Phenylenes, Studies of Physical and Cellular Imaging Behavior

Synthesis of chain length-controlled oligo-p-phenylenes, formylation through post-functionalization, photophysical and biochemical properties are described herein. Synthesis of oligo-p-phenylene oligomers with controlled chain length is facilitated by using multivalent dendritic Pd^II catalysts. Suzuki–Miyaura oligomerization of bromo/iodophenylboronic acids in H₂O:THF (3:1) solutions, mediated by one to three generations of poly(propyl ether imine) (PETIM) dendritic catalysts, leads to oligomers with degree of polymerization (DP) 14–26. Upon synthesis, the oligomers are subjected to formylation with the aid of Vilsmeier–Haack reaction. The resulting formylated oligomers are soluble in organic solvents and aqueous solutions, thereby permitting a series of studies to be conducted solution. A Stokes shift of ~70 nm occurs in the emission spectrum of the formylated oligomer (λ _em = 470; λ _em = 340) and a quantum yield of 12% in MeOH solution. The particle sizes vary between 100 nm in MeOH and 410 nm in 25% MeOH in water solution. The functionalized oligomers show morphological features, primarily consisting of twisted rod-like morphologies. The cytotoxicities of functionalized oligomer with DP14 are adjudged to be 85 and 105 μg mL⁻¹ in HEK293 and HeLa cells. The emission behavior of the functionalized oligo-p-phenylenes is taken advantage to assess the cellular imaging properties of HEK293 and HeLa cells.