Hyperconjugation-induced chromism in linear responsive polymers

Responsive polymers, undergoing changes in light absorption and emission properties in response to stimuli, have been extensively investigated as key smart materials. Here, we report the nature underlying the optical and spectroscopic responses in linear polydiacetylenes, responsive conjugated polymers well-known for a blue-to-red transition upon specific stimuli. By means of a theoretical strategy mimicking entire empirical treatments, we reveal that hyperconjugation between the side chain and conjugated backbone signals their response: the first understanding at the electronic state level, unlike molecular conformational arguments prevailing since topochemical polymerization was discovered by Wegner in 1972. We provide quantitative exploration of (i) the thermochromic response, and (ii) applied functions showing reversible and irreversible chromism. The present work should lead to a new angle for polydiacetylene-based materials design from the hyperconjugation perspective.