Single-bond-linked and vinylene-bridged azulenyl bis(squaraine) dyes: design, synthesis and molecular self-assembly behaviors

Abstract

In this work, two azulenyl bis(squaraine) dyes were designed and synthesized, whose main structural difference lies in the connection model between two monomeric units. Their self-assembly behaviors were investigated in mixed solvents of different polarities, compound concentrations and temperatures. In particular, for the single-bond-linked squaraine dimer, J-aggregate nanosheets could be formed in a hexane system mixed with small amounts of tetrahydrofuran as a co-solvent. Meanwhile, additional absorption bands were observed in the second near-infrared (NIR-II, 1000–1700 nm) region for vinylene-bridged bis(squaraine) aggregates, elucidating the impact of the spacer unit on interchromophoric interaction modes. Moreover, in comparison with the monomer compound, organic field-effect transistor and morphological characterizations revealed that dimerization has a significant influence on the charge carrier mobility and thermal responsiveness of film aggregates. This study provides a promising chemical modification approach to improve assembly behavior and optoelectronic performance.