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

Abstract

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.