Abstract: ESIPT-capable pyrimidine-based compounds featuring short O–H⋯N intramolecular hydrogen bonds, 2-(2-hydroxyphenyl)-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidine (HL1) and 2-(2-hydroxyphenyl)-4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-methylpyrimidine (HL2), were synthesized by the condensation of 4-hydrazinyl-2-(2-hydroxyphenyl)-6-methylpyrimidine with acetylacetone and dibenzoylmethane. In solution, HL1 and HL2 do not exhibit luminescence due to efficient non-radiative deactivation through S0/S1 conical intersection of non-planar nature, whereas in the solid state they show dual emission associated with phosphorescence at 500–700 nm and fluorescence at 400–500 nm. Phosphorescence is not related to ESIPT and occurs in the enol form (E) in accordance with the Kasha rule, TE1 → SE0. In contrast, fluorescence follows the proton transfer process and corresponds to the anti-Kasha SK2 → SK0 transition in the tautomeric keto form (K), which is caused by an extraordinarily large S2–S1 energy gap (ca. 0.9 eV) and, consequently, low S2 → S1 internal conversion rate. The fluorescence/phosphorescence intensity ratio is temperature-dependent for HL1, resulting in the emission color change from yellow-green at 77 K to blue-green at 300 K, while HL2 glows in the orange region in the whole temperature range owing to the predominant contribution of phosphorescence.

Cite: Shekhovtsov N.A. , Nikolaenkova E.B. , Ryadun A.A. , Vorobyeva S.N. , Krivopalov V.P. , Bushuev M.B.
Dual emission of ESIPT-capable 2-(2-hydroxyphenyl)-4-(1H-pyrazol-1-yl)pyrimidines: interplay of fluorescence and phosphorescence
New Journal of Chemistry. 2023. V.47. N13. P.6361-6377. DOI: 10.1039/d3nj00570d WOS РИНЦ

Dates:

Accepted:	Mar 4, 2023
Published print:	Mar 6, 2023

Identifiers:

Web of science	WOS:000948764400001
Elibrary	61489765
OpenAlex	W4323342626

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