Selective Chirality-Driven Photopolymerization of Diacetylene Crystals.

Area of Science:

• Supramolecular chemistry
• Polymer chemistry
• Crystal engineering

Background:

• Diacetylene monomers are building blocks for advanced materials.
• Chiral auxiliaries can influence molecular packing and reactivity.
• Hydrogen bonding plays a crucial role in directing supramolecular assembly.

Purpose of the Study:

• To investigate the impact of chirality on diacetylene monomer crystal packing and polymerization.
• To explore the relationship between molecular configuration and solid-state reactivity.
• To understand the photophysical properties of resulting polymers.

Main Methods:

• Synthesis of chiral diacetylene monomers with enantiopure and meso configurations.
• X-ray crystallography to determine solid-state structures and intermolecular interactions.
• Thermal and photochemical polymerization studies.
• Density Functional Theory (DFT) computations for electronic structure analysis.

Main Results:

• Two diacetylene monomers, DA2 (enantiopure S,S) and DA4 (meso R,S), were synthesized and characterized.
• X-ray structures revealed supramolecular arrangements driven by hydrogen bonding, with closer proximity in DA4.
• DA4 underwent facile photochemical polymerization (minutes) and slow thermal polymerization (days) to form PDA5, while DA2 remained unreactive.
• DFT calculations identified charge-transfer states and indicated that PDA5 is nonemissive, with coloration from polymer backbone excitation.

Conclusions:

• Subtle changes in carbon configuration of chiral groups on diacetylene monomers lead to drastic selectivity in polymerization.
• Crystal engineering via hydrogen bonding and molecular arrangement is critical for controlling solid-state reactivity.
• The resulting polymer PDA5 exhibits unique optical properties arising from its backbone structure.