Thiophene is one of the most commonly used moieties in conjugated materials, whereas its oxygen congener, furan, is much less frequently encountered due to the susceptibility of furan toward light- and oxygen-induced degradation. In an effort to stabilize furans, three difurans, bridged by Ph2Si, Ph2Ge, and PhP(O), were synthesized. Each bridged difuran has Me3Si groups at the 2- and 6-positions. All of the bridged difurans were found to be stable under ambient conditions. Since it is known that electron-deficient furans exhibit improved stability, the stability of the bridged difurans is attributed, in part, to the p-block elements, which lower the LUMO levels of the molecules through σ*−π* conjugation. Single-crystal X-ray diffraction studies of the phosphorus-bridged species showed that the structure is similar to that of the known thiophene analogue, but with bond lengths consistent with the reduced aromaticity of furan. All of the p-block bridged difurans show strong absorption in the UV region and intense emissions with quantum yields ranging from 0.30 to 0.80. DFT calculations indicate that the frontier molecular orbitals of bridged difurans are slightly higher than those of their thiophene counterparts. In order to demonstrate the synthetic potential of bridged difurans, the phosphorus-bridged difuran was converted to its 2,6-dibromo derivative, which in turn was copolymerized with (9,9-dioctyl-9H-fluorene-2,7-diyl)bis(trimethylstannane) to form the stable conjugated polymer PDFP-F. The phosphorus-bridged difuran was also reduced from its phosphine oxide form and then quaternized with methyl triflate to produce the corresponding air-stable phosphonium salt.

The anionic ring-opening copolymerization of 1-(methylsulfonyl)aziridine (MsAz) and 1-(sec-butylsulfonyl)aziridine (sBsAz) produces a soluble random copolymer P(MsAz-r-sBsAz), which can subsequently be converted to linear poly(ethylenimine) (lPEI). The copolymerization of MsAz and sBsAz is living and allows for the synthesis of copolymers with low molecular weight distributions. Sequential anionic polymerization of MsAz and sBsAz with 2-methyl-1-(methylsulfonyl)aziridine (MsMAz) creates P(MsAz-r-sBsAz)-b-P(MeMsAz). Removal of the sulfonyl groups from P(MsAz-r-sBsAz)-b-P(MsMAz) gives lPEI-b-poly(propylenimine). For the first time, lPEI can be synthesized by a controlled anionic polymerization.

A series of substituted 9-borafluorenes were studied both experimentally and computationally in order to assess substituent effects on the optical and electronic properties and the stability of 9-borafluorenes. The previously unknown 9-substituted-9-borafluorenes MesFBF (MesF = 2,4,6-tris(trifluoromethyl)phenyl), TipBF(OMe)2 (Tip = 2,4,6-tris(triisopropyl)phenyl, (OMe)2= methoxy at the borafluorene 3 and 6 positions), and iPr2NBF (iPr2N = diisopropylamino) were synthesized and structurally characterized. The previously reported TipBF, ClBF (9-chloro-9-borafluorene) and tBuOBF (9-(tert-butoxy)-9-borafluorene) were also included in this study. All of the aryl borafluorenes (TipBF, TipBF(OMe)2, MesFBF), and tBuOBF are moderately air-stable. Both iPr2NBF and ClBF degrade rapidly in air. Cyclic voltammogram measurements and density functional theory (DFT) calculations reveal that (a) borafluorenes have higher electron affinities relative to comparable boranes and (b) substituents have a strong influence on the lowest unoccupied molecular orbital (LUMO) levels of borafluorenes but less influence over the highest occupied molecular orbital (HOMO) levels. The DFT calculations show that, in general, borafluorenes exhibit low electron reorganization energies, a predictor of good electron mobility. However, the MesF group, which is finding popularity as a stabilizing group in borane chemistry, significantly increases the electron reorganization energy of MesFBF compared to the other borafluorenes. The Lewis acidities of the borafluorenes were probed using Et3P═O as a Lewis base (the Gutmann–Beckett method) and found to be dictated primarily by steric considerations. Calculated fluoride affinities (Lewis acidities) correlate with the LUMO energies of the borafluorenes. UV–visible and fluorescence spectroscopic measurements showed that compared to the Tip substituent, the MesF, Cl, and methoxy groups only cause subtle changes to the optical properties of the borafluorenes. The absorption spectra of both iPr2NBF and tBuOBF are blue-shifted due to substituent π-backbonding with the p-orbital on boron. The results of this study provide insights into substituent effects on conjugated boron systems and will help in the design of future boron containing materials.