Phenylene alkylene dendrons with site-specific incorporated fluorescent pyrene probes

This report deals with the synthesis and the spectroscopic properties of two second generation (G2) dendrons with site-specific incorporated phenyl pyrene derivatives as solvatochromic fluorescent probes. The generations that do not carry the probe are equipped with volume dummies, pyrene moieties that do not show a solvatochromic effect. Two complementary G2 phenylene alkylene dendrons were synthesized using Suzuki-Miyaura cross coupling. Most of the reactions used in the 10-step sequence generating the target compounds proceeded in good yields. The incorporated probes can be selectively photoexcited and show solvatochromic shifts that are of the same magnitude as for the free probes in a homogeneous solvent environment. In addition to the charge-transfer fluorescence, a broad emission band is observed that is assigned to an intramolecular exciplex formation between the aryl pyrene chromophores.