Alkylthieno[2,3‑d][1,3]thiazole as a Dual-Mode Design Principle for Single-Beam Unidirectional Spontaneous Surface-Relief Gratings in Push–Pull Azobenzenes

Yet achieving macroscopic single-beam unidirectional SP-SRG in covalently bonded systems with a value of maximum absorption wavelength (λ_absmax) above 500 nm remains elusive due to the trade-off between red-shifted absorption and chain mobility.

Here, the alkylthieno[2,3-<i>d</i>][1,3]thiazole (<b>TTz</b>) heterocycle resolves this trade-off through a dual-mode design principle: its electron-withdrawing nature extends absorption range from 400 to 650 nm and the value of λ_absmax to 536 nm (film spin-coated from THF), while systematic modulation of alkyl substituent bulkiness (i.e., methyl, <i>n</i>-butyl, 2-ethylhexyl) on <b>TTz</b> simultaneously controls chromophore aggregation and decreases the polymer’s glass transition temperature (<i>T</i>_g) from 144 to 75 °C. A family of polymethacrylate azobenzene homo- and copolymers (<b>PMAzo-TTz</b>, <b>P1a-P4c</b>) was synthesized and characterized, demonstrating that this <i>T</i>_g tuning operates independently of the chromophore’s electronic structure, a key feature enabling decoupled material optimization.