Chameleon‐Like Thermochromic Luminescent Materials with Controllable Response Behaviors for Multilevel Security Printing

Abstract

Materials exhibiting reversible changes of their photoluminescence properties upon exposure to heat have an immense potential in various advanced photonic applications. Particularly, the control over an on‐demand response of thermochromic luminescent materials (TLMs) similar to a chameleon is of great importance. However, it is still difficult and challenging to achieve it. Therefore, this paper reports a simple and effective way to construct TLMs, which involves the incorporation of the metal–ligand complexes into polyethylene glycol (PEG). Ratiometric or off–on response modes of these TLMs can be tuned by incorporating metal complexes based on either Zn2+ or Co2+ into PEG and by taking advantage of reversible metal–ligand coordination, dissociation, or excited‐state conformation changes of the resulting materials. Moreover, by choosing PEG matrices with different molecular weights, the thermochromic transition temperatures of these TLMs can be tuned. It is also demonstrated that the controllable response behavior of these chameleon‐like TLMs can be used in applications related to real‐life anti‐counterfeiting and security printing. This work opens novel opportunities for the development of smart materials with controllable responses useful for advanced photonic applications.

Stimuli‐responsive photofunctional materials for green and security printing

“…Importantly, they can be used for achieving multilevel security printing and different information can be accessed at various temperatures. 20,21 5 | HALOCHROMIC MATERIALS FOR GREEN AND SECURITY PRINTING…”

“…D, Multilevel security printing—different information can be accessed at various temperatures. Reproduced with permission 20 . Copyright 2019, Wiley‐VCH.…”

“…The PL properties of the prepared thermochromic materials change significantly upon heating, and they can display various thermochromic transition temperatures by changing the different molecular‐weight PEG matrices (Figure 7D). Importantly, they can be used for achieving multilevel security printing and different information can be accessed at various temperatures 20,21 …”

“…In addition, in the era of information explosion, there is a growing demand for paper document security since information leakage brings enormous security issues. [19][20][21][22][23][24] They can lead to severe consequences, such as war outbreak, economic loss, social problems, and so on. As a result, the realization of information security printing on paper is urgently needed and has attracted wide interests.…”

“…The development of functional papers that can reuse multiple times in a “writing‐erasing‐writing” cycle is an effective way to solve these problems and achieve green printing. In addition, in the era of information explosion, there is a growing demand for paper document security since information leakage brings enormous security issues 19‐24 . They can lead to severe consequences, such as war outbreak, economic loss, social problems, and so on.…”