Microwave-Assisted Synthesis of 1,5- and 2,6-Linked Naphthylene-Based Ladder Polymers

Abstract

A series of novel arylene ladder polymers incorporating conjugated 1,5- and 2,6-naphthylene building blocks were synthesized. The polyketone ladder polymer precursors were prepared via a palladium-mediated Suzuki-type cross-coupling reaction using both conventional and microwave heating. While the 2,6-naphthylene polyketone precursor (2,6-NPK) was accessible from both heating protocols, the 1,5-naphthylene linked polyketones were only accessible via microwave-assisted (μW) procedures, and the polymer 1,5-NLP2 is the first example of a ladder polymer consisting exclusively of alternating six-membered rings prepared from this reaction sequence. The solution optical spectra of the final naphthylene ladder polymers exhibit the characteristic spectral shapes with a steep absorption edge and a vibronic fine structure common to fully rigidified ladder structures. The structural modification of the substitution pattern and the linkage positions at the naphthylene unit allows some tuning of the absorption and emission bands of the ladder polymers. The 2,6-naphthylene derivative exhibits an intense blue photoluminescence, while the two 1,5-naphthylene-linked ladder polymers exhibit a red shift of the 0−0 electronic transitions, leading to a blue-green photoluminescence.