TY - JOUR

T1 - Interplay of the Cu⋯Cu distance and coordination geometry as a factor affecting the quantum efficiency in dimeric copper(i) halide complexes with derivatives of 4-pyrazolylpyrimidine-2-thiol

AU - Skvortsova, Sofia V.

AU - Verkhov, Fyodor K.

AU - Nikolaenkova, Elena B.

AU - Rakhmanova, Marianna I.

AU - Kokina, Tatiana E.

AU - Sukhikh, Taisiya S.

AU - Shekhovtsov, Nikita A.

AU - Bushuev, Mark B.

N1 - The synthesis of the ligands and complexes and the interpretation of the experimental and theoretical results were funded by the Russian Science Foundation (grant no. 25-23-00375, https://rscf.ru/project/25-23-00375/ ). The elemental analysis data, X-ray single-crystal data, and the H NMR, C NMR, IR and emission spectra were obtained using the equipment of the Multi-Access Chemical Research Centre SB RAS at Nikolaev Institute of Inorganic Chemistry SB RAS and N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS with support from the Ministry of Science and Higher Education of the Russian Federation. The authors thank the XRD Facility of NIIC SB RAS and personally thank V. N. Yudin, D. V. Kochelakov, L. V. Zargarova and D. A. Ulybin for the X-ray diffraction data collection. The Siberian Branch of the Russian Academy of Sciences (SB RAS) Siberian Supercomputer Centre is gratefully acknowledged for providing supercomputer facilities. M. B. B. acknowledges the access to the Computational Centre of the Novosibirsk State University.

PY - 2025

Y1 - 2025

N2 - Two bicyclic pyrazolylpyrimidine compounds, 2-benzylthio-4-(3,5-dimethyl-1H-pyrazol-1-yl)pyrimidine (LH) and 2-benzylthio-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidine (LMe), were synthesized and studied as ligands for the preparation of copper(i) halido complexes. In the solid state, LH and LMe demonstrate dual excitation-wavelength dependent emission, i.e. fluorescence at higher excitation energies and phosphorescence at lower excitation energies due to the presence of a heavy sulphur atom. The reactions of LH and LMe with CuBr and CuI afforded a series of centrosymmetric binuclear complexes of the [Cu2L2Hal2] type (L = LH, Hal = Br, I; L = LMe, Hal = I). The possibility of rotation of the benzylthio group relative to the pyrazolylpyrimidine core leads to the isolation of two polymorphic modifications of the copper(i) iodido complex with LH, which differ by the Cu⋯Cu distance by more than 0.2 Å (2.86 Å for [Cu2(LH)2I2] (form I)vs. 2.65 Å for [Cu2(LH)2I2] (form II)). The isolation of the [Cu2(LH)2I2] complex in two different crystalline forms made it possible to reveal the influence of a rarely explored factor, namely the change in the Cu⋯Cu distance in a single molecule, on the photoluminescence quantum efficiency. Two structural indices, τdim, which showcases the degree of merging of CuLHal monomers into the centrosymmetric [Cu2L2Hal2] dimers, and τplan, which characterises the degree of planarization of the N2CuHal2CuN2 unit, were introduced and used for combined experimental and theoretical analyses of the relation between the structure of the complexes and their luminescence. All complexes exhibit phosphorescence of the ligand-to-halide charge transfer (LXCT) character in the orange region. According to TD-DFT calculations, an increase in the Cu⋯Cu distance facilitates structural rearrangement in the T1 state followed by a rapid decrease in the T1-S0 energy gap and subsequent non-radiative decay via electron-phonon coupling, which substantiates the higher photoluminescence quantum yield (PLQY) of [Cu2(LH)2I2] (form II) (Cu⋯Cu 2.65 Å) compared to that of [Cu2(LH)2I2] (form I) (Cu⋯Cu 2.86 Å).

AB - Two bicyclic pyrazolylpyrimidine compounds, 2-benzylthio-4-(3,5-dimethyl-1H-pyrazol-1-yl)pyrimidine (LH) and 2-benzylthio-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidine (LMe), were synthesized and studied as ligands for the preparation of copper(i) halido complexes. In the solid state, LH and LMe demonstrate dual excitation-wavelength dependent emission, i.e. fluorescence at higher excitation energies and phosphorescence at lower excitation energies due to the presence of a heavy sulphur atom. The reactions of LH and LMe with CuBr and CuI afforded a series of centrosymmetric binuclear complexes of the [Cu2L2Hal2] type (L = LH, Hal = Br, I; L = LMe, Hal = I). The possibility of rotation of the benzylthio group relative to the pyrazolylpyrimidine core leads to the isolation of two polymorphic modifications of the copper(i) iodido complex with LH, which differ by the Cu⋯Cu distance by more than 0.2 Å (2.86 Å for [Cu2(LH)2I2] (form I)vs. 2.65 Å for [Cu2(LH)2I2] (form II)). The isolation of the [Cu2(LH)2I2] complex in two different crystalline forms made it possible to reveal the influence of a rarely explored factor, namely the change in the Cu⋯Cu distance in a single molecule, on the photoluminescence quantum efficiency. Two structural indices, τdim, which showcases the degree of merging of CuLHal monomers into the centrosymmetric [Cu2L2Hal2] dimers, and τplan, which characterises the degree of planarization of the N2CuHal2CuN2 unit, were introduced and used for combined experimental and theoretical analyses of the relation between the structure of the complexes and their luminescence. All complexes exhibit phosphorescence of the ligand-to-halide charge transfer (LXCT) character in the orange region. According to TD-DFT calculations, an increase in the Cu⋯Cu distance facilitates structural rearrangement in the T1 state followed by a rapid decrease in the T1-S0 energy gap and subsequent non-radiative decay via electron-phonon coupling, which substantiates the higher photoluminescence quantum yield (PLQY) of [Cu2(LH)2I2] (form II) (Cu⋯Cu 2.65 Å) compared to that of [Cu2(LH)2I2] (form I) (Cu⋯Cu 2.86 Å).

UR - https://www.mendeley.com/catalogue/184bcfbe-c951-3b7a-ba9c-a8ad7cce899d/

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-105005336814&origin=inward&txGid=2c7c1b230499c1f0c5a25469c110b544

U2 - 10.1039/d5dt00498e

DO - 10.1039/d5dt00498e

M3 - Article

C2 - 40365655

JO - Dalton Transactions

JF - Dalton Transactions

SN - 1477-9226

ER -