ctDNA-Driven Helical Assembly of Achiral Dimers: Simultaneous Activation of Three-Photon Fluorescence and Circularly Polarized Luminescence.

The development of organic materials capable of simultaneously exhibiting circularly polarized luminescence (CPL) and high-order multiphoton excited fluorescence (H-MPEF) is highly desirable for near-infrared (NIR) imaging and sensing of chiral microenvironments in biomolecular systems, yet remains a significant challenge. Herein, we report a facile chiral assembly strategy that enables concurrent CPL and three-photon excitation fluorescence (3PEF) through the interaction of achiral pyridinium-based homodimers with calf thymus DNA (ctDNA). Specifically, two homodimers, designated LD and FD, were precisely designed and synthesized to feature distinct spatial configurations. The linear LD, with its narrow molecular thickness, binds preferentially to the minor groove of ctDNA via electrostatic interactions. This association facilitated efficient chirality transfer from the DNA scaffold while simultaneously triggering 3PEF through effective suppression of nonradiative decay, ultimately yielding a pronounced CPL signal. Collectively, this work not only provided a viable strategy for designing achiral small organic molecules compatible with nucleic acid but also elegantly addresses the longstanding challenge of achieving integrated CPL and NIR-window fluorescence imaging.