In this work, a bicyclo[4.4.1]undecane scaffold is used to hold oligo(phenylene ethynylene) units in a cofacially stacked arrangement along the entire length of the conjugated units. We study the impact that the resulting strong interchain interactions have on the photophysical properties. The length of the individual oligomer branches was varied from three to five rings to investigate the effect of conjugation on the electronic properties of the stacked segments. Absorption and fluorescence spectra were recorded and compared to those of the corresponding unstacked analogues. Time-dependent density functional theory calculations were carried out and helped to rationalize the low-energy features present in the fluorescence spectra of the stacked systems. The calculations indicate that the low-energy emissions are due to the presence of excimer-like states. The stronger intensity of the low-energy fluorescence band observed in the five-ring stacked system compared to the three-ring analogue is attributed to the smaller activation barrier that separates the local intrachain state and the excimer-like state in the former compound.

The synthesis of novel conjugated polymers by acyclic diyne metathesis (ADIMET) is reported. These polymers are hybrids between poly(p-phenylenevinylene) and poly(p-phenyleneneethynylene) (PPE). They contain phenylene, ethynylene, and vinylene groups (⋮PhPh, PPVE). Simple in situ catalysts formed from Mo(CO)6 and 4-chlorophenol were used to metathesize the dipropynyl(tetraalkyl)stilbene monomers. The monomers are made by a combination of Horner reactions and Heck-type couplings. The PPVEs form in high yields and are structurally defined. They show degrees of polymerization (P n ) of 30−220 repeating units (i.e. 60−450 benzene rings), demonstrating that the presence of the double bonds does not interfere with alkyne metathesis. The PPVEs were structurally characterized by XRD and electron microscopy. They show fibrillar and network-type morphologies, which should make them interesting for applications in molecular electronics. Solid samples of PPVEs display powder XRD patterns almost identical to those of the PPEs. PPVEs thus assume similar doubly lamellar structures as the PPEs. The aggregation behavior of PPVEs was studied. In addition, ADIMET to a poly(2,7-fluorenyleneethynylene) carrying unsaturated side chains is reported. In this case the presence of unsaturation does neither interfer with efficient alkyne metathesis.

Three tethered diphenylacetylene derivatives were prepared by alkyne metathesis. In these cycles, the twist angle between the two benzene rings is variable and determined by the nature of the linker. The engineering of the twist angle leads to a change of the UV−vis spectra of the cycles. The larger the twist angle in the macrocycles, the more blue shifted their λ max (UV−vis), the lower their fluorescence quantum yield, and the lower field shifted their 13 C NMR signals of the alkyne carbons are.

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