Macroscopic Orientational Gold Nanorods Monolayer Film with Excellent Photothermal Anticounterfeiting Performance

Abstract Constructing 2D gold nanorods monolayer films with precise particle assembly is of great importance to fundamental and real applications. However, it is usually difficult to achieve macroscopic size, freestanding feature, high density of particle packing, and precisely controllable particle orientation in monolayer films. In this work, a macroscopic, uniform, freestanding orientational monolayer film is facilely and controllably prepared through precise assembly of asymmetrically modified gold nanorods at water–oil interface. The assembling morphologies can be controlled through regulating the interaction between gold nanorods by varying the amounts and sites of modified molecules. The intriguing tunable assemblies exhibit not only adjustable absorption spectrum in a wide range attributed to different particle coupling, but also optimized photothermal conversion capability under low energy density (0.08 W cm^‐2). Together with a commercial thermochromic dye, the patterned assemblies show excellent photothermal anti‐counterfeiting performance by reproducing accurate full images in 20 s that are invisible after laser off in 10 min. The excellent laser writing performance is also demonstrated by writing any information on thermochromic dye‐coated assemblies. With the advantages of being macroscopic, equipment‐free, transferable, scalable and with high photothermal conversion capability, the orientational monolayer films pave the way for on‐demand design of sensing and device applications.