Zinc(ii) and Cadmium(ii) Metal-Organic Frameworks Based on the Amide- Functionalized Tetracarboxylate Ligand: Synthesis, Crystal Structure, and Luminescent Properties

Series of Cadmium-Organic Frameworks Based on Mixed Flexible and Rigid Ligands: Single-Crystal-to-Single-Crystal Transformations, Sorption, and Luminescence Properties

“…Both coordination polymers 1 ·H 2 O and 2 demonstrate an abnormally strong dependence of the maximum emission wavelength on the excitation wavelength (Figure S29). The bathochromic shift of the maximum of the photoluminescence emission wavelength is about 100 nm for compound 1 ·H 2 O and about 150 nm for compound 2 when the excitation wavelength changes from 300 to 540–560 nm. Such a strong dependence of the emission wavelength on the excitation wavelength can be conditioned by several emission bands at 440, 500–525, and 600–625 nm (Figure S29).…”

Luminescence of ESIPT-capable zinc(ii) complexes with a 1-hydroxy-1H-imidazole-based ligand: exploring the impact of substitution in the proton-donating moiety

“…Recently, we demonstrated that 1-hydroxy-1H-imidazoles decorated with proton-accepting groups at position 2 of the imidazole ring and a pyridin-2-yl group at position 4 to assist the N 3 imidazolic atom in binding metal ions can act as ESIPT-capable ligands and coordinate Zn 2+ ions without deprotonation (HL p and HL q , see Scheme 2). Since Zn 2+ ions are known to be able to enhance the emission originating from the ligand-centered excited states due to so-called chela-tion-enhanced fluorescence (CHEF) effect, [125][126][127][128][129][130] their coordination by ESIPT-capable 1-hydroxy-1H-imidazoles led to a noticeable increase in the photoluminescence quantum yield (PLQY). 131,132 Moreover, the emission of the free ligands and complexes appeared to be tunable through the extension of the π-conjugation in the proton-accepting part of the molecule.…”

Complexes on the Base of a Proton Transfer Capable Pyrimidine Derivative: How Protonation and Deprotonation Switch Emission Mechanisms

“…Azole and benzazole ESIPT-capable derivatives are workhorses in the area of ESIPT studies. − The most common molecular pattern of these compounds which is widely relied upon in the design of ESIPT dyes includes the proton-accepting azole/benzazole moiety combined with the proton-donating 2-hydroxyphenyl group or its analogues introduced in the α position to the azolic N atom. In contrast, pyrimidine derivatives are relatively rarely used for the design of ESIPT-fluorophores in comparison with azole and benzazole ones. ,− However, being combined with suitable proton-donating groups, they can serve as proton-accepting moieties. ,, Moreover, introducing additional donor groups in the pyrimidine core can lead to more complex molecular architectures of pyrimidine-based compounds suitable for binding metal ions and providing numerous sites for protonation, including isomeric ones. ,, In turn, the synthesis of isomeric ESIPT-capable compounds allows researchers to shed more light on the impact of structural factors on ESIPT and on relationships between ESIPT and luminescence. − The coordination of conventional dyes and ESIPT emitters to metal ions with d electronic configuration such as Zn 2+ is known to enhance the quantum efficiency of emission. − Earlier we demonstrated that emissions of 4-(1 H -pyrazol-1-yl)-6-(2-hydroxyphenyl)­pyrimidines and 2-(2-hydroxyphenyl)-4-(1 H -pyrazol-1-yl)­pyrimidines, which belong to two different isomeric families (Chart ), share such a common feature as dual emission associated with singlet-to-singlet and triplet-to-singlet transitions, which is contributed by anti-Kasha fluorescence of the tautomeric form. ,, However, their coordination behavior toward Zn 2+ ions appeared to be quite different, whereas the 4-(1 H -pyrazol-1-yl)-6-(2-hydroxyphenyl)­pyrimidine derivative can bind Zn 2+ ions through the N,N-site of the molecule, which produces multicolor emission of the complex, 2-(2-hydroxyphenyl)-4-(3,5-dimethyl-1 H -pyrazol-1-yl)­pyrimidine derivatives cannot do this. We associated this with steric effects imposed by methyl and phenyl substituents introduced in positions 3 and 5 of the pyrazolyl group.…”