Regiosymmetric Dibutyl-Substituted Poly(3,4-propylenedioxythiophene)s as Highly Electron-Rich Electroactive and Luminescent Polymers

We report the synthesis of the dibutyl derivative of poly(3,4-propylenedioxythiophene) as a regiosymmetric and soluble electroactive and photoluminescent conjugated polymer obtained in the neutral form by a Grignard metathesis coupling reaction. Molecular weights have been characterized by gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI−TOF) mass spectrometry, the latter showing end groups due to H/H, H/Br, and Br/Br termini. Solution-cast films of PProDOT-Bu2 are reddish-purple with a λmax value of 544 nm as deposited (576 nm after electrochemical annealing) and an electronic band gap of 1.8 eV. In solution, the polymer displays a strong deep red photoluminescence, and transient absorption studies reveal that direct excitation also affords a long-lived triplet state with low-to-moderate quantum efficiency. The photoluminescence is considerably weaker in the solid state, presumably due to rapid nonradiative decay at interchain trap sites. The polymer is easily oxidized with an E 1/2 of ∼0.2 V vs Ag/Ag+ when prepared either by solution casting of the chemically synthesized polymer or by direct electrodeposition and provides a distinct electrochromic switch from a deep red-purple to a highly transmissive sky blue. Similar spectral changes are observed upon solution doping, and conducting films (up to 7 S/cm) have been prepared which exhibit a high level of ambient stability.