Alkyl/Cycloketonic Modulations in Photoinitiator Molecular Engineering for Efficient Multiphoton Polymerization ^†

Comprehensive Summary Dibenzylidene ketone (DBK) photoinitiators (PIs) hold promise for one‐photon polymerization (OPP) and two‐photon lithography (TPL), owing to easily synthesized extended π‐conjugated frameworks via one‐step aldol condensation. However, industrial adoption is limited by poor solubility and critical OPP reactivity/TPL processability mismatch. Herein, we report a dual‐parameter molecular engineering strategy for tert ‐butylcarbazole‐functionalized DBK PIs, tuning N ‐alkyl chains (methyl, ethyl, n ‐butyl, n ‐dodecyl) and cyclic ketone spacers (C5: cyclopentanone; C6: cyclohexanone) to optimize polymerization properties. For OPP, C5‐DBKs exhibit enhanced visible photosensitivity, enabling rapid kinetics under 405–520 nm LEDs; N ‐dodecyl derivatives show excellent photobleaching and deep curing. For TPL, C5‐DBKs have superior two‐photon absorption ( σ TPA ) but C6‐DBKs offer better solubility (1 wt% in PETA) and act as efficient one‐component TPL PIs. Using a 780 nm fs laser, N1C6/PETA enables high‐precision fabrication: threshold matrix writing exhibits wide processing window and good uniformity, achieving sub‐200 nm resolution (167 nm linewidth at 45 mW, 50 mm·s –1 ) and high‐fidelity microlens arrays. Complex 3D microstructures (intricate logos, sub‐micron text, Chinese jade belt bridge, nanoscale‐pore photonic crystals) demonstrate versatility in photonics, metamaterials and micro‐pattern anti‐counterfeiting. This work establishes OPP/TPL structure‐activity relationships (SARs) and a versatile molecular design platform for industrial coatings and micro/nano‐manufacturing.