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 tert-butyl- and methyl-substituted alkoxy­methylene–diethynyl­benzene copolymers with different degrees of polymerization and the corresponding dimers are synthesized. The tert-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 tert-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 tert-butyl-substituted copolymers. On the other hand, the corresponding less bulky, methyl-substituted alkoxy­methylene tethered copolymers exhibit emission around 400–450 nm attributed to the through-space interactions between nonadjacent diethynyl­benzene chromophores. The variations of folding nature of these two kinds of copolymers are determined by the size of the substituents, methyl versus tert-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.