Thermally Activated Fluorescence vs Long Persistent Luminescence in ESIPT-Attributed Coordination Polymer

Abstract

Excited-state intramolecular proton transfer (ESIPT) molecules demonstrating specific enol-keto tautomerism and the related photoluminescence (PL) switch have wide applications in displaying, sensing, imaging, lasing, etc. However, an ESIPT-attributed coordination polymer showing alternative PL between thermally activated fluorescence (TAF) and long persistent luminescence (LPL) has never been explored. Herein, we report the assembly of a dynamic Cd­(II) coordination polymer (LIFM-101) from the ESIPT-type ligand, HPI2C (5-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazol-1-yl)­isophthalic acid). For the first time, TAF and/or color-tuned LPL can be achieved by controlling the temperature under the guidance of ESIPT excited states. Noteworthily, the twisted structure of the HPI2C ligand in LIFM-101 achieves an effective mixture of the higher-energy excited states, leading to ISC (intersystem crossing)/RISC (reverse intersystem crossing) energy transfer between the high-lying keto-triplet state (T n (K*)) and the first singlet state (S1(K*)). Meanwhile, experimental and theoretical results manifest the occurrence probability and relevance among RISC, ISC, and internal conversion (IC) in this unique ESIPT-attributed coordination polymer, leading to the unprecedented TAF/LPL switching mechanism, and paving the way for the future design and application of advanced optical materials.

Construction of a series of Ln-MOF luminescent sensors based on a functional “V” shaped ligand

“…4 In 2022, Su et al reported an ESIPT-attributed Cd-MOF which achieved thermally activated fluorescence and long persistent luminescence. 5 As a common type of industrial ingredient, phenylenediamine was added to lots of chemical products. When the content of phenylenediamine is too higher, environmental security and human health might be damaged.…”

Coordination Assemblies Based on a Methylthio Carboxylic Ligand: Syntheses, Structures and Luminescent Properties

“…Each Cu 2+ is pentacoordinated to four O atoms from four MBA linkers with the bond length of 1.975(2), 1.969(2), 1.977(2) and 1.969(2) Å for Cu-O1, Cu-O2, Cu-O3 and Cu-O4, respectively. The angles of O1-Cu1-O2, O3-Cu1-O4, O1-C1-N1 were 88.31 (8), 89.35(0) and 100.94(0)°, respectively. The distance between two copper atoms is 2.641 Å, suggesting existence of Cu-Cu bonding interaction.…”

“…[1,2] Reasonable ligand design and selection of metal ions can realize multi-functionalization of CP materials. [3,4] These CPs have been applied to the fields of luminescence, [5][6][7][8][9] sensing, [10][11][12][13] catalysis, [14][15][16] etc. The coordination groups in the ligands are usually pyridine, imidazole, hydroxyl, carboxyl, sulfhydryl, methylthio units containing nitrogen, sulfur and oxygen atoms, while the metal ions are usually transition, rare-earth, and a small number of main-group metals.…”

N-Hydroxy–N-oxide photoinduced tautomerization and excitation wavelength dependent luminescence of ESIPT-capable zinc(ii) complexes with a rationally designed 1-hydroxy-2,4-di(pyridin-2-yl)-1H-imidazole ESIPT-ligand

“…20 references. 38,66–88 For the most part, these complexes are based on aromatic carboxylic acids ( e.g. 3-hydroxy-2-quinoxalinecarboxylic acid, 2,5-dihydroxyterepthalic acid) and 2-(1 H -imidazol-2-yl)phenol derivatives decorated by aromatic carboxylic acid groups.…”

“…3-hydroxy-2-quinoxalinecarboxylic acid, 2,5-dihydroxyterepthalic acid) and 2-(1 H -imidazol-2-yl)phenol derivatives decorated by aromatic carboxylic acid groups. 66–88 Metal ions used in the synthesis of ESIPT-complexes are mostly the ions of divalent metals of the second and twelfth groups of the periodic table (Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Zn 2+ , Cd 2+ ) and the ions of trivalent lanthanides (Sm 3+ , Eu 3+ , Tb 3+ , Gd 3+ , Er 3+ , Nd 3+ ). Metal–organic frameworks (MOFs) based on divalent ions show fluorescence.…”