Supramolecular aggregation for manipulating molecular packing by endgroups leading to mechanochromic fluorescence

Mechanochromic fluorescence (MCF) materials show great potential in many fields. But it is still a great challenge to rationally design proper molecular structures and tune their molecular packing and MCF properties, especially for molecules with planar backbones. Herein, ladder-type molecules based on planar indeno[1,2-b] thiophene 1,1-dioxides (ITDO) backbones are designed. The moderate dipole moment originating from the donor-acceptor structure of backbone and steric sidechains leads to a loose supramolecular aggregation with dimeric structures. And the emission properties could be tuned by introducing halogen endgroups onto the backbones. As a result, ITDO-Cl and ITDO-Br showed stronger intermolecular interactions, leading to dual emission band and MCF properties. In contrast, ITDO-H and ITDO-I crystal showed single monomer emission peak without mechanochromism.

Automated summary

Ladder-type molecules based on planar ITDO backbones were designed, with halogen endgroups tuning their emission properties. Halogen endgroups resulted in stronger intermolecular interactions, leading to dual emission bands and MCF properties.