Design and Synthesis of Photofluorochromic Coordination Polymers Featuring Dual-Mode Output for Dynamic Anticounterfeiting

Photofluorochromic
compounds exhibit dual-mode output
characteristics
of photochromism and fluorescence, enabling high-security anticounterfeiting.
However, constructing such materials is difficult due to the competition
between the photoinduced electron transfer (PIET) process and fluorescence.
Herein, we propose that prolonging the conjugation length of the ligand
to form a charge transfer excited state may be an efficient method
for constructing photofluorochromic materials. Accordingly, we designed
and synthesized a ligand featuring an extended conjugation structure
(denoted as (HL)Cl = 1-((4′-carboxy-[1,1′-biphenyl]-4-yl)methyl)-[4,4′-bipyridin]-1-ium)
chloride. Through a thermal reaction with metal ions and a second
ligand, two coordination polymers [Cd(L)(HL1)]·DMF·2H2O (1, H3L1 = 1,3,5-benzene­tricarboxylic
acid) and [Zn2(L)(L2)(H2O)2]·2H2O (2, H4L2 = 1,2,4,5-benzene­tetracarboxylic acid) were successfully synthesized.
Both compounds exhibit excellent photochromic and luminescent properties.
Their photochromic processes show excellent reversibility and can
be repeated for more than five cycles. Both compounds exhibited excellent
luminescence after photochromism, which was attributed to promoted
charge transfer, resulting from the extended conjugation length of
the ligand. These dual-mode signal output materials demonstrate significant
potential for anticounterfeiting applications. Based on their dual-mode
behavior, this study demonstrates various anticounterfeiting technologies,
including banknote anticounterfeiting. The dynamic photochromic process
combined with the luminescent authentication significantly enhances
anticounterfeiting security, confirming the great feasibility of these
dual-mode output materials for high-level security applications. This
work is expected to provide new insights into the development of photofluorochromic
coordination polymers.

光致荧光变色（Photofluorochromic）化合物兼具光致变色与荧光双模式输出特性，可应用于高安全性防伪领域。然而，由于光诱导电子转移（Photoinduced Electron Transfer, PIET）过程与荧光效应存在竞争，这类材料的构建颇具挑战。在此，我们提出通过延长配体（Ligand）的共轭长度以构建电荷转移激发态，或许是构建光致荧光变色材料的有效策略。据此，我们设计并合成了一种具有扩展共轭结构的配体（记为(HL)Cl = 1-((4'-羧基-[1,1'-联苯基]-4-基)甲基)-[4,4'-联吡啶]-1-鎓）氯化物。通过与金属离子和第二配体发生热反应，我们成功合成了两种配位聚合物：[Cd(L)(HL₁)]·N,N-二甲基甲酰胺（DMF）·2H₂O（编号1，H₃L₁=1,3,5-苯三甲酸）以及[Zn₂(L)(L₂)(H₂O)₂]·2H₂O（编号2，H₄L₂=1,2,4,5-苯四甲酸）。两种化合物均展现出优异的光致变色与发光性能。其光致变色过程具备出色的可逆性，可重复进行五次以上循环。两种化合物在光致变色后仍保持优异的发光性能，这归因于配体共轭长度延长所促进的电荷转移过程。这类双模式信号输出材料在防伪领域展现出巨大应用潜力。基于其双模式响应特性，本研究展示了多种防伪技术方案，其中包括钞票防伪。动态光致变色过程与发光认证相结合，显著提升了防伪安全性，证实了这类双模式输出材料在高等级安全应用中的良好可行性。本研究有望为光致荧光变色配位聚合物的发展提供全新的研究思路。