Boosting Second Harmonic Generation in Hemicyanine/Silicalite-1 Films through External Surface Hydrophobic Modification

Second-order nonlinear optical (2NLO) materials are essential for practical photonic devices.Here, we demonstrate that external surface hydrophobic modification of silicalite-1 (SL1) films markedly enhances 2NLO activity by improving the degree of uniform orientation (DUO) of incorporated hemicyanine (HC-n) dyes.Attaching chlorodimethyloctadecylsilane to bare SL1 (bSL1) yielded strongly hydrophobic octadecylmodified SL1 (o-mSL1) (water contact angle: 75 ∘ vs. 15 ∘ ), promoting unidirectional HC-n inclusion via hydrophobic-hydrophobic interactions.Although the number density in o-mSL1 is slightly reduced due to steric hindrance at channel entrances, the substantially higher DUO produces a significantly enhanced relative second harmonic generation intensity (rel-I 2 ).A maximum rel-I 2 of 479.4 % was achieved for HC-22@o-mSL1, surpassing 400.0 % for HC-15@bSL1, confirming that surface hydrophobicity directly governs DUO and 2NLO performance.This approach offers a practical route to high-performance inorganic-organic 2NLO materials.