Energy‐Efficient Bulk Photoalignment of Main‐Chain Liquid Crystalline Polymers Enabled by In Situ Monitoring

Abstract Main‐chain liquid crystalline polymers (LCPs) offer tunable anisotropic properties essential for applications in optical data storage, soft robotics, and sensing. While photoalignment provides a powerful, non‐contact route to control mesogen orientation, its use has been largely constrained to sub‐micron films due to light attenuation and weak anchoring. Here, a strategy is reported for bulk photoalignment of azobenzene‐containing main‐chain LCPs, enabled by in situ optical monitoring and systematic structure–processing analysis. By tuning molecular weight, azobenzene content, cooling rate, and sample thickness, key parameters are revealed that govern alignment efficiency. Optically anisotropic films with order parameters ( S ) ≥0.25 and thicknesses up to 130 µm are achieved, surpassing conventional alignment limits. Azobenzene– r –C6M copolymers align rapidly and are stabilized through crystallization without chemical crosslinking. For example, 2 µm‐thick copolymer films reach S = 0.63 within 6 min using 420 nm light exposure (30 mW cm −2 ), while 200 nm homopolymers require 34 min to reach S = 0.48. Reversible QR code write–read–erase cycles highlight potential in rewritable optical media. This work introduces a scalable approach for reconfigurable alignment in LCPs and advances the design of bulk‐responsive anisotropic materials.