Determination of the Orientation of Pendants on Rigid‐Rod Polymers

Abstract

Bis-norbornene and bis-cyclobutene with different kinds of linkers have been extensively used for the synthesis of double stranded ladderphanes under ruthenium-or molybdenum-catalyzed ring opening metathesis polymerization (ROMP) conditions. The key to the success relies on the selective formation of comb-like polynorbornenes or polycycloubtenes, where pendants are all aligned towards similar direction. This minireview summarizes various methods (chemical methods, spectroscopic means, and nonlinear optical measurements) for determining the comb-like conformations of pendants on these rigid-rod polymers. The approach is based on the proximal relationship between adjacent pendants. Interactions between these adjacent pendants would enable a change in chemical reactivity [a] Prof. T.

Aggregation-Enhanced Excimer Emission of Tetraarylethene Linkers in Ladderphanes

“…Ladderphanes 3 and 4 would be more rigid than single-stranded polynorbornene 8 . It is known that adjacent linkers in 3 and 4 are essentially eclipsed, whereas the dihedral angles between neighboring pendants of 8 are nonzero . Accordingly, the excimer might be formed more readily from the linkers in 3 and 4 than from the pendants in 8 .…”

“…Rigid species such as oligoaryls have been used as linkers to connect two polynorbornene or polycyclobutene backbones via ester linkages, leading to the formation of ladderphanes. The adjacent linkers in these ladderphanes are separated by 5.5 or 4.5 Å, depending on the nature of polymeric backbones. , Thus, the polymer can be viewed as a deck of nicely packed chromophores insulated by two hydrophobic polymeric backbones. The ester linkage in 1 and 2 would be slightly flexible to enable the two neighboring linkers being closer, and, hence, exciton coupling between these two adjacent chromophores might take place.…”

A Fischer-Type Ruthenium Carbene Complex as a Metathesis Catalyst for the Synthesis of Enol Ethers

“…In the past 15 years, our endeavor has focused on the 1a -catalyzed ROMP of the aniline-appended norbornene 11a to give stereoselectively the corresponding isotactic polymer 12 having all double bonds in an E configuration and pendants directed toward a similar direction . The aniline pendants in 11 can be considered as a remote substituent to the norbornene.…”

“…As part of our continuing interests in the ROMP of aniline-appended strained-ring monomers, we have synthesized the cyclopropene derivatives 22a and 22b spirally connected to the aniline pendant . As mentioned above, norbornene with the aniline pendant 11b readily undergoes ROCM with EVE to yield 13 .…”