Iterative Synthesis of Dynamic Conjugated Oligomers Displaying Length-Dependent Configuration Metastability,...

The emergence of structure and function at the mesoscale is critical for the design of complex molecular materials. In this work, we report an iterative liquid-phase construction of precision conjugated oligomers with alternating di- and tetra-arylsubstituted alkene (DAA and TAA) building blocks. Due to the dynamically reversible isomerization of TAA building blocks in the backbone, this system exhibited a complex library of constitutional stereoisomers with configurational metastability, as characterized by HRMS, chiral HPLC, and 2D excitation-emission fluorescence mapping analysis. The dynamic oligomer system exhibits aggregation-induced absorption shifts and state-dependent fluorescence and shows constitutional responses to thermal and light stimuli. During the self-assembly process, mesoscale helicity emerges in the P5 oligomer and evolves into regular helices (40-66 nm pitch) in the P9 oligomer, which can also be tuned by side group modulation. Experimental and computational studies suggest a dynamic transition of conjugated backbone conformations with increasing chain length from linear, rich in trans-alkenes, to twisted with alternating trans- and cis-alkenes, resulting in a stereoregular triangular chain segment for secondary structure generation and property emergence.