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Substituent-Dependent Photophysical Properties Due to the Thorpe–Ingold Effect on Foldings of Alternating Substituted Methylene–Diethynylbenzene Copolymers: A Comparison of Carbon versus Silicon Tethers
Alternating <i>tert</i>-butyl- and methyl-substituted
alkoxyÂmethylene–diethynylÂbenzene copolymers with
different degrees of polymerization and the corresponding dimers are
synthesized. The <i>tert</i>-butyl-substituted polymers
show prominent emissions around 350–400 owing to ground state
interactions between adjacent chromophores separated by a substituted
methylene group. The Thorpe–Ingold effect exerted by the bulky <i>tert</i>-butyl group would compress the bond angle at the methylene
tether and may alter the overall folding scaffold of the polymer.
The interactions between adjacent chromophores would be significantly
enhanced in these <i>tert</i>-butyl-substituted copolymers.
On the other hand, the corresponding less bulky, methyl-substituted
alkoxyÂmethylene tethered copolymers exhibit emission around
400–450 nm attributed to the through-space interactions between
nonadjacent diethynylÂbenzene chromophores. The variations of
folding nature of these two kinds of copolymers are determined by
the size of the substituents, methyl versus <i>tert</i>-butyl,
resulting in different photophysical behaviors. The emission properties
of the methyl-substituted copolymers behave similarly to those of
related silylene-tethered copolymers in the literatures, albeit the
relative intensity in the blue light emission is somewhat smaller
in methylene-bridged copolymers than in silylene-linked copolymers