Pentiptycene building blocks derived from nucleophilic aromatic substitution of pentiptycene triflates and halides.

The nucleophilic aromatic substitution (S(N)Ar) reactions of the nitro-substituted pentiptycene triflate 15 with LiBr and LiI and the resulting halides 18 and 19 with N(3)(-), CN(-), and ArS(-) in DMF provide an efficient route toward pentiptycene halides and dihalides and other new pentiptycene building blocks. The reactivity of diaminopentiptycene in Pd-catalyzed C-N coupling reactions is also demonstrated.

Central-ring functionalization and application of the rigid, aromatic, and H-shaped pentiptycene scaffold.

The progress of pentiptycene chemistry is reviewed. Pentiptycene belongs to the iptycene family and possesses a rigid, aromatic, and H-shaped scaffold. An important feature for pentiptycene vs. triptycene is the presence of a 'sterically shielded' central benzene ring. Such a feature has led to the use of pentiptycene as a conformational regulator and in the formation of functional molecules, including fluorescent chemosensors, molecular machines, low dielectric constant materials, and porous solids. The synthesis of these materials relies on central-ring prefunctionalized pentiptycene building blocks. A useful approach toward the preparation of these building blocks is the derivatization of pentiptycene quinone.

Synthesis and properties of a fluorene-capped isotruxene: a new unsymmetrical star-shaped pi-system.

An unsymmetrical star-shaped pi-system (1) with an isotruxene core and three fluorene arms has been synthesized, and its photophysical, electrochemical, and thermochemical properties have been investigated and compared with the corresponding symmetrical truxene derivatives 2a-d (Kanibolotsky, A. L.; Berridge, R.; Skabara, P. J.; Perepichka, I. F.; Bradley, D. D. C.; Koeberg, M. J. Am. Chem. Soc. 2004, 126, 13695-13702). Stronger electronic couplings between the arms in 1 vs 2a-d lead to lower optical band gap, larger splitting in oxidation potentials, and superior thermostability. [structure: see text]

Synthesis of new halogenated pentiptycene building blocks.

The synthesis of central-ring halogenated pentiptycene phenols 12-14 and dihalogenated pentiptycenes 15-17 is reported. Their utilities as building blocks for preparing new pentiptycene-derived pi-conjugated systems through the Sonogashira, Heck, and Suzuki reactions are also demonstrated.

Probing the intrachain and interchain effects on the fluorescence behavior of pentiptycene-derived oligo(p-phenyleneethynylene)s.

The synthesis, crystal structure, and fluorescence behavior of acetylene-bridged pentiptycene dimer (2), trimer (3), and tetramer (4) are reported. For comparison, a phenylene-pentiptycene-phenylene three-ring system (5) is also investigated. As a result of the unique intrachain pentiptycene-pentiptycene interactions in 3 and 4, their twisted conformers are populated in polar solvents and at low temperatures, and the phenomenon of nonequilibration of excited rotational conformers is observed. Twisting of the pi-conjugated backbones leads to blue-shifted absorption and fluorescence spectra and increased fluorescence quantum yields and lifetimes. The fluorescence spectra of 2-4 undergo small red shifts but large intensity variations in the 0-1 vs 0-0 bands on going from solutions to thin solid films, which can be accounted for by the reabsorption effect. However, the reduction in fluorescence quantum yields for 2-4 in films vs solutions is mainly attributed to efficient interchain exciton migration to nonfluorescent energy traps. In contrast, the behavior of nonequilibration of excited rotamers is not observed for 5 in solutions. Compound 5 forms J-type aggregates through terminal phenylene pi-stackings in the solid state, resulting in a new absorption band at 377 nm and large red shifts of the structured fluorescence spectra.