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

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

Journal

Inorganic Chemistry
ISSN: 0020-1669

Output data

Year: 2023, DOI: 10.1021/acs.inorgchem.3c02036

Authors

Shekhovtsov Nikita A. ¹ , Vorob’eva Sofia ¹ , Nikolaenkova Elena B. ² , Ryadun Alexey A. ¹ , Krivopalov Viktor P. ² , Gourlaouen Christophe ³ , Bushuev Mark B. ¹

Affiliations

1	Nikolaev Institute of Inorganic Chemistry of the Siberian Branch of the RAS
2	N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry of Siberian Branch of Russian Academy of Sciences
3	Laboratoire de Chimie Quantique, Institut de Chimie, UMR 7177 CNRS-Université de Strasbourg, 4 rue Blaise Pascal, Strasbourg Cedex 67070, France

A rare example of pyrimidine-based ESIPT-capable compounds, 2-(2-hydroxyphenyl)-4-(1H-pyrazol-1-yl)-6-methylpyrimidine (HL ), was synthesized (ESIPT-excited state intramolecular proton transfer). Its reactions with zinc(II) salts under basic or acidic conditions aforded a dinuclear [Zn2L2Cl2] complex and an ionic (H2L) [ZnCl4]2(-) · 3H2O solid. Another ionic solid, (H2L)Br, was obtained from the solution of HL acidifed with HBr. In both ionic solids, the H ion protonates the same pyrimidinic N atom that accepts the O−H···N intramolecular hydrogen bond in the structure of free HL , which breaks this hydrogen bond and switches of ESIPT in these compounds. This series of compounds which includes neutral HL molecules and ionic (L (-)) and (H2L(+)) species allowed us to elucidate the impact of protonation and coordination coupled deprotonation of HL on the photoluminescence response and on altering the emission mechanism. The neutral HL compound exhibits yellow emission as a result of the coexistence of two radiative decay channels: (i) T → S0 phosphorescence of the enol form and (ii) anti-Kasha S2 → S0 fuorescence of the keto form, which if feasible due to the large S2 −S1 energy gap. However, owing to the efcient nonradiative decay through an energetically favorable conical intersection, the photoluminescence quantum yield of HL is low. Protonation or deprotonation of the HL ligand results in the signifcant blue-shift of the emission bands by more than 100 nm and boosts the quantum efciency up to ca. 20% in the case of [Zn2L2Cl2] and (H2L)4 [ZnCl4]2 ·3H2O. Despite both (H2L)4[ZnCl2]2 ·3H2O and (H2L)Br have the same (H2L(+)) cation in the structures, their emission properties difer signifcantly, whereas (H2L)Br shows dual emission associated with two radiative decay channels: (i) S1 → S0 fuorescence and (ii) T1 → S0 phosphorescence, (H2L)4[ZnCl2]2 ·3H2O exhibits only fuorescence. This diference in the emission properties can be associated with the external heavy atom efect in (H2L)Br, which leads to faster intersystem crossing in this compound. Finally, a huge increase in the intensity of the phosphorescence of (H2L)Br on cooling leads to pronounced luminescence thermochromism (violet emission at 300 K, sky-blue emission at 77 K).

Shekhovtsov N.A. , Vorob’eva S. , Nikolaenkova E.B. , Ryadun A.A. , Krivopalov V.P. , Gourlaouen C. , Bushuev M.B.
Complexes on the Base of a Proton Transfer Capable Pyrimidine Derivative: How Protonation and Deprotonation Switch Emission Mechanisms
Inorganic Chemistry. 2023. DOI: 10.1021/acs.inorgchem.3c02036 WOS РИНЦ

Submitted:	Jun 20, 2023
Published online:	Oct 2, 2023

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