Borafluorenes and polyborafluorenes boron doped varients of fluorene
A series of novel boron containing variants of fluorene were synthesized. Boron was incorporated synthetically via lithium halogen exchange and Grignard reaction pathways. Once incorporated, the borafluorene could be polymerized or undergo further functionalization via Yamamoto and Stille coupling reactions. This incorporation of boron into a conjugated system imparted Lewis acidic and electron deficient properties into a conjugated system. It is our hope that this will dope fluorene and create novel n-type semiconductors. A novel polymer of borafluorene, poly(9-borafluorene) (P9BF) was synthesized. HOMO and LUMO levels of P9BF were estimated by cyclic voltammetry. As predicted in prior DFT studies, P9BF has a reduced band gap and a lower lying LUMO compared with polyfluorene. To examine how the HOMO and LUMO levels of borafluorene systems could be tuned, copolymers of 9-borafluorene were synthesized. Four of the copolymers were a series of donor-acceptor (DA) type copolymers. A borafluorene-fluorene (P9BF-OF) copolymer and borafluorene-diketopyrrolopyrrole (P9BF-DPP), as an acceptor-acceptor (AA) copolymer were also synthesized. The series of DA copolymers showed higher energy HOMO and LUMO levels in correlation with the relative donating ability of the donor monomer. P9BF-OF has a reduced LUMO level in comparison with P9BF. P9BF-DPP has a very low band gap (1.8eV), with absorption well into the near-IR region. To examine ways to make borafluorene more air stable, a series of borafluorenes bearing bismethylmethoxyphenyl (BMMP) ligands were investigated. Interestingly, ii bismethylmethoxyphenyl-borafluorene (BMMP-BF) exhibits an exceptionally large Stokes shift of 16000 cm-1. To extend the conjugation and change the Stokes shift, thiophene containing derivatives BMMP-BF-T, BMMP-BF-2T, and BMMP-BF-3T were synthesized. These thiophene containing compounds exhibited anomalous two wavelength fluorescence. During our fluoride titration experiments, we noticed spectral impurities when using tetrabutylammonium fluoride (TBAF) as our fluoride source. Examining this more closely, we found that commercial samples of TBAF were found to absorb light at 295 and 370 nm and fluoresce as 435 nm. This was not expected for analytically pure TBAF, so we concluded that there must be an impurity present in commercial TBAF. The source of this impurity was found to be I3- which occurs from the oxidation of I-.
Networked Digital Library of Theses and Dissertations