Thermochromism and supramolecular chirality of the coumarin-substituted polydiacetylene LB films

• Novel coumarin-substituted diacetylene monomer (CODA) is synthesized.
• PCODA films exhibit reversible thermochromism and strong chiral properties.
• CODA monomer can be photo-dimerized to form a novel gemini-type DCODA monomer.
• PDCODA films show enhanced thermal stability, but weaker chiral properties.
• The dimerization of head groups inhibits the chirality formation of PDA chain.

Herein, a novel single-chain coumarin-substituted diacetylene monomer (CODA) was synthesized. CODA LB films exhibited obvious chirality although CODA monomer was achiral. Upon UV irradiation, CODA LB films could be polymerized into blue form and exhibit reversible thermochromism and chiroptical properties. Strong intermolecular interaction among the coumarin chromophores was assumed to be responsible for the complete reversibility of absorption and chiroptical changes for PCODA films upon thermal stimulus. And the helical packing of the coumarin chromophores seemed to play a dominating role in the subsequent formation of the helical PDA backbone. Moreover, the single-chain CODA monomer could be further photo-dimerized, and a novel gemini-type diacetylene monomer (DCODA) could be prepared. The effects of the photo-dimerization reaction of the coumarin moieties on the thermochromism and chiroptical properties of the resulting PDCODA films had been evaluated. The dimerization of head groups would enhance the thermal stability of PDCODA films but inhibit the chirality formation for PDA backbone.

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