Electroactive and luminescent polymers: new fluorene-heterocycle-based hybrids

The synthesis, characterization, and electrochromic properties of copolymer s derived from 9,9-dialkyl-2,7-dibromofluorene (18a, alkyl=C10H21; 24, alky l=Et) and pyrrole, thiophene, 3,4-ethylenedioxythiophene, and furan are des cribed. Two synthetic routes to 9,9-diethyl-2,7-bis(pyrrol-2-yl)fluorene (3 0) afford product in 30% and 20% yields, respectively. Monomer 30 undergoes electropolymerizationto yield electroactive polymer films. The lowest mono mer oxidation potential (E-p,E-m=0.4 V vs. Ag/Ag+) is found in tetraethylam monium tosylate (TEATOS)-CH3CN, but film formation is slow. Spectroelectroc hemical analysis of poly(30) reveals a band gap at 2.4 eV and upon polymer oxidation, two low energy absorptions peaking at 1.2 and 2.2 eV appear. Thi s phenomenon is attributed to formation of bipolaron bands between the vale nce and conduction bands. Soluble fluorene-heterocycle polymers 34a-d have been synthesized by the Stille coupling reaction of 18a and 2,5-bis(trimeth ylstannyl)thiophene (21a), 5,5'-bis(trimethylstannyl)-2,2'-bithiophene (21b ), 2,5-bis(trimethylstannyl)-3,4-ethylenedioxythiophene (21c), and 2,5-bis( trimethylstannyl)furan (22), respectively, in high yields. The NMR spectra are consistent with the proposed structures of the polymers 34a-d, and no e vidence of ring opening of the furyl unit in 34d is seen in the NMR and IR spectra. The molecular weights of 34a-d are in the range of 8000 g mol(-1) with polydispersity indices (PDI) of 2. Polymers 34a-c have band gaps measu red at 2.4 eV, while polymer 34d has its gap at 2.6 eV. Polymers 34a-c unde rgo solution doping with SbCl5 to form new low energy bipolaron bands at th e expense of the absorption in the UV-VIS. However, polymer 34d does not ox idatively dope with SbCl5.