Synergetic Spin-Crossover and Luminescence in a Fe(II) Complex with Aggregation-Induced Emission and Twisted Intramolecular Charge Transfer

We report the precise design and synthesis of a fluorescent ligand (E)-4-(((2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)methylene)amino)-N,N-diphenylaniline (bpp-TPA), achieved through the covalent integration of a fluorophore triphenylamine (TPA) with the coordination subunit 2,6-bis(pyrazol-1-yl)pyridine (bpp), which provides a N6 octahedral coordination environment optimized for Fe(II), allowing us to prepare a mononuclear complex [Fe(bpp-TPA)2]·(CF3SO3)2, bpp-TPA-Fe. This complex exhibits a reversible thermally induced spin-state switching with a T1/2 of 311 K. Meanwhile, the fluorescent intensity of bpp-TPA-Fe intensified distinctly upon spin-state conversion, reaching its maximum emission at 360 K, clearly indicative of a synergistic coupling between the SCO process and luminescent behavior. Benefiting from its carefully engineered intramolecular motional dynamics and donor–acceptor (D–A) molecular architecture, bpp-TPA-Fe simultaneously exhibits pronounced aggregation-induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties. Furthermore, large bathochromic shifts in the emission spectra with the increase in solution polarity are realized in this complex. This work exemplifies a highly precise molecular design strategy to construct multifunctional molecular materials with tunable magneto-optical properties, opening avenues for next-generation smart material applications.

本工作报道了一种荧光配体(E)-4-(((2,6-二(1H-吡唑-1-基)吡啶-4-基)亚甲基)氨基)-N,N-二苯基苯胺(bpp-TPA)的精准设计与合成：该配体通过将荧光团三苯胺(triphenylamine, TPA)与配位亚基2,6-二(吡唑-1-基)吡啶(2,6-bis(pyrazol-1-yl)pyridine, bpp)共价整合得到，可提供适配Fe(II)的六配位八面体配位环境，借此我们制备得到单核配合物[Fe(bpp-TPA)₂]·(CF₃SO₃)₂，即bpp-TPA-Fe。该配合物展现出可逆的热致自旋交叉行为，其自旋转变温度T₁/₂为311 K。与此同时，bpp-TPA-Fe的荧光强度在自旋态转变过程中显著增强，并在360 K时达到发射峰值，清晰表明自旋交叉（spin crossover, SCO）过程与发光行为之间存在协同耦合效应。得益于精心调控的分子内运动动力学与供体-受体（donor-acceptor, D-A）分子结构，bpp-TPA-Fe同时展现出显著的聚集诱导发射（aggregation-induced emission, AIE）与扭曲分子内电荷转移（twisted intramolecular charge transfer, TICT）特性。此外，该配合物的发射光谱随溶液极性增大呈现显著的红移。本工作展示了一种高精度分子设计策略，可用于构建兼具可调磁光特性的多功能分子材料，为下一代智能材料的应用开辟了新路径。