π-Congested poly(paraphenylene) from 2,2′,6,6′-tetraphenyl-1,1′-biphenyl units: synthesis and structural characterization

The synthesis of poly(paraphenylene)s (PPPs) bearing sterically pi-congested 2,2',6,6'-tetraphenyl-1,1'-biphenyl (1) units has been achieved for the first time. By enhancing the synthesis of 1, followed by its polymerization, we were able to compare the photophysical properties of the oligomeric and polymeric fractions with non-crowded PPPs. This revealed significant pi-orbital interactions along the paraphenylene backbone of the pi-congested systems together with through-space conjugation among the pi-orbitals of the stacked peripheral phenyl rings, resulting in an increased effective conjugation length and a remarkable bathochromic shift in absorption.