On the Rigidity of Polynorbornenes with Dipolar Pendant Groups

Abstract

A range of polynorbornenes (PNBs) with fused dipolar pendant groups at C-5,6 positions was synthesized by ring-opening metathesis polymerization catalyzed by a ruthenium carbene complex (Grubbs I). Photophysical studies, EFISH measurements, and atomic force microscopy images have been used to investigate the structures and morphology of these polymers. These results suggest that the polymers may adopt rigid rod-like structures. The presence of the double bonds in PNBs appeared to be indispensable for the rigidity of the polymers. Interaction between unsaturated pendant groups may result in coherent alignment leading to a rod-like structure.

Oligomeric Tectonics: Supramolecular Assembly of Double‐Stranded Oligobisnorbornene through π–π Stacking

“…[3] As described previously, [3,4] the ferrocene moiety is employed as a linker for these double-stranded polymers because the spacing occupied by the ferrocene moiety appears to be within the limit of span for the vinylcyclopentane monomeric unit in polynorbornenes (5)(6). [3,4,51,52] It has certain rigidity but is also somewhat flexible to accommodate the pending norbornene moieties in 3 in close proximity for the polymerization process. In addition, it may serve as a kind of stuffing to prop up the two polymeric backbones.…”

“…[4] Isotacticity and trans double bonds of the backbones [51,54] were adopted for the modeling. The groups of carboxy and methyl ester on the cyclopentadienyl moieties are anti relative to the ferrocene moiety.…”

“…Our recent advances in the development of single-and double-stranded oligonorbornenes, [50] for example, analogues of 1 (Scheme 1), provide a unique platform for the exploration of enhanced nonlinear optical properties, [51,52] electron transfer propagating along the linearly aligned redox linkers, [53] template-directed replication of complementary oligonorbornenes, [3] oligomeric chirality, [5] and fundamental stereochemistry. [4,54,55] However, it is puzzling that submicron-long strings are sometimes observed from dropcast films.…”

Excimer Formation in a Confined Space: Photophysics of Ladderphanes with Tetraarylethylene Linkers

“…The absorption spectrum of monomer 10 a is essentially the sum of the absorptions of tetraarylethylene 6 and aminobenzoate 8 c ( Figure 1). [25] Like other single-and double-stranded polynorbornenes, [7,[14][15][16]19] the absorption due to the aminobenzoate chromophores in ladderphane 2 a (l max = 314 nm) exhibited a hypsochromic shift in comparison with that of 10 a (l max = 320 nm, Figure 1), which may be due to release of strain from the norbornene moiety. [28] On excitation at 350 nm, no emission was observed from solutions of 10 a, 6, and 8 c in CH 2 Cl 2 (1.0 10 À5 to 1.0 10 À3 m).…”

“…[7,14] This kind of polymer can also be considered as a linear array of cofacially arranged arenes in a polymer matrix. Depending on the nature of the polymeric backbones in 1, the spacing between arene linkers would be 5.5 for double-stranded polynorbornenes [15] and around 4.5 for polycyclobutene-based ladderphanes. [16] Significant perturbation of photophysical properties has been observed in these ladderphanes in comparison with those of corresponding monomers, although these distances are somewhat longer than those in typical p-p interactions between aromatic layers, such as those in DNA molecules [17] and in graphite.…”