Electrostatic self-assembled design strategy for tetracarboxylic Nickel(II) naphthalocyanine ultrathin film for high-performance nonlinear optical properties

• Ultrathin film containing tetracarboxylic Nickel(II) naphthalocyanine were prepared.
• The face to face molecular arrangement in films increased molecular coupled effect.
• An enhanced Raman spectroscopy phenomenon for P/NiNcC4 film was analyzed.
• Higher γ value for P/NiNcC4 film (7.0 × 10−27 esu) was obtained than NiNcC4 solution.

The rational design and controllable preparation of the solid film with strong molecular coupled effect represents a long-standing challenge for developing advanced practical nonlinear optical (NLO) materials. Here, we report a general electrostatic self-assembled strategy toward fabricating tetracarboxylic Nickel(II) naphthalocyanine (NiNcC4) ultrathin film on solid substrate with an ordered molecular arrangement based on the controllable deposition of anionic NiNcC4 naphthalocyanine and cationic polydiallydimethyldiallylammonium chloride (PDDA). The 30-bilayer P/NiNcC4 film shows an ordered conformation of face-to-face molecular arrangement, ultrathin thickness (126.6 nm) and a Raman enhancement phenomenon, and exhibits a high second-order molecular hyperpolarizability γ of 7.0 × 10−27 esu, which is three orders larger than that of NiNcC4 aqueous solution, demonstrating the potential of strongly molecular coupling effects for advanced self-assembled systems.

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