Dibenzofulvene (DBF) was polymerized using anionic initiators to afford a vinyl polymer. Oligo(DBF)s having from two to eight side-chain fluorene moieties bearing different chain-terminal groups were isolated by preparative size-exclusion chromatography. The structures of the isolated oligomers were revealed by single-crystal X-ray and (1)H NMR analyses. Both in solution and in crystal, the in-chain fluorene moieties stacked on top of each other, while the terminal conformation varied depending on the terminal group. These conformational characteristics were supported by molecular mechanics and dynamics calculations. The oligomers and polymers indicated hypochromism and red shift in UV absorption spectra and exclusive excimer emission in fluorescence spectra. In addition, reduced oxidation potentials were observed for the oligomers in electrochemical analyses, which suggests charge delocalization over the pi-stacked electron systems. The photophysical and electrochemical effects increased with the chain length of the oligomers and leveled off around the chain length of an oligomer consisting of five fluorene units.

Diphenylethylene (DPE) is known as a representative vinyl compound that does not produce a homopolymer through any kind of catalysis, and its low reactivity has been ascribed to steric reasons. [1][2][3] Here we report that dibenzofulvene (DBF), 4 whose structure is closely related to that of DPE, affords a polymer by anionic, radical, and cationic catalyses. DBF differs from DPE only in the fact that the two phenyl groups are connected to each other to form a fused ring structure. In addition, the absorption and emission features of the polymerization products suggested that they possess a novel "π-stacked structure" in which the aromatic groups in the side chain are stacked on top of each other.

Hole drift mobility of poly(dibenzofulvene) was found to be 2.7 × 10−4 cm2V−1s−1 at 299 K at a field strength of 7 × 105 Vcm−1 by the time-of-flight (TOF) measurement on a cast film containing 2,4,7-trinitrofluorenylidene-9-malononitrile as an electron acceptor. This value is higher than that of main-chain π-conjugating poly(π-phenylenevinylene) (1 × 10−5 cm2V−1s−1), is comparable to that of main-chain σ-conjugating poly(methylphenylsilane) (1 × 10−4 cm2V−1s−1), and is slightly lower than that of Se (10−4 cm2V−1s−1 order), an inorganic semiconductor.

The molecular parameters governing charge transport along a pi-stacked fluorene chain in poly(dibenzofulvene) are studied by a joint experimental and theoretical approach involving high-resolution gas-phase photoelectron spectroscopy and quantum-mechanical methods. We specifically investigate the electronic couplings between fluorene moieties as well as the intramolecular reorganization energies, for both holes and electrons. Our results indicate that a pi-stacked fluorene chain favors hole transport over electron transport. The values for electronic couplings and reorganization energies estimated here are compared with those derived recently for pentacene.