Photo-responsive chemical systems enabling multiscale structural ordering

Beyond elemental composition and molecular structure, ordered multiscale architectures (self-assembled structure, crystal structure, phase structure, etc.) play a comparably important role in determining material functions, especially the optoelectronic properties. Light, a unique external stimulus with superior spatiotemporal resolution and non-invasive nature, provides unparalleled capabilities for dynamically constructing and manipulating such ordered structures. Since previous reviews on light-responsive materials have generally overlooked how light can govern multiscale structural ordering, this review comprehensively surveys the rapidly advancing field of photo-responsive chemical systems designed to achieve and control multiscale structural ordering. We begin by elucidating the fundamental photochemical and photophysical mechanisms at the molecular level, which serve as the primary triggers for molecular structural, configurational, or conformational transformations. Based on these events that initiate molecular perturbation, the core of the review critically examines several key light-mediated strategies for constructing and manipulating ordered hierarchical architectures, notably photo-triggered polymerization-induced self-assembly, liquid crystal-assisted phase structural amplification, photo-induced self-assembly mediated by host-guest interaction, and the emerging paradigm of photoexcitation-induced assembly (PEIA). We discuss how these strategies successfully translate molecular or nanoscale events into well-defined, macroscopic ordered states in real time and in situ. Finally, we provide a forward-looking perspective on the existing challenges and promising future research directions.