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. 2022 Nov 19;27(22):8029.
doi: 10.3390/molecules27228029.

4-(Aryl)-Benzo[4,5]imidazo[1,2- a]pyrimidine-3-Carbonitrile-Based Fluorophores: Povarov Reaction-Based Synthesis, Photophysical Studies, and DFT Calculations

Victor V Fedotov  1 , Maria I Valieva  1 , Olga S Taniya  1 , Semen V Aminov  1 , Mikhail A Kharitonov  1 , Alexander S Novikov  2 , Dmitry S Kopchuk  1 , Pavel A Slepukhin  1 , Grigory V Zyryanov  1 , Evgeny N Ulomsky  1 , Vladimir L Rusinov  1 , Valery N Charushin  1
Affiliations

4-(Aryl)-Benzo[4,5]imidazo[1,2- a]pyrimidine-3-Carbonitrile-Based Fluorophores: Povarov Reaction-Based Synthesis, Photophysical Studies, and DFT Calculations

Victor V Fedotov et al. Molecules. .

Abstract

A series of novel 4-(aryl)-benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitriles were obtained through the Povarov (aza-Diels-Alder) and oxidation reactions, starting from benzimidazole-2-arylimines. Based on the literature data and X-ray diffraction analysis, it was discovered that during the Povarov reaction, [1,3] sigmatropic rearrangement leading to dihydrobenzimidazo[1,2-a]pyrimidines took place. The structures of all the obtained compounds were confirmed based on the data from 1H- and 13C-NMR spectroscopy, IR spectroscopy, and elemental analysis. For all the obtained compounds, their photophysical properties were studied. In all the cases, a positive emission solvatochromism with Stokes shifts from 120 to 180 nm was recorded. Aggregation-Induced Emission (AIE) has been illustrated for compound 6c using different water fractions (fw) in THF. The compounds 6c and 6f demonstrated changes in emission maxima or/and intensities after mechanical stimulation.

Keywords: Povarov reaction; aggregation-induced emission; aza-Diels–Alder reaction; benzimidazole; fluorescence; mechanochromic properties; oxidation; pyrimidine.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Nucleophilic substitution of hydrogen (SNH) in 2-phenyl-2H-benzo[4,5]imidazo[1,2-a][1,2,3]triazolo[4,5-e]pyrimidine [42].
Scheme 2
Scheme 2
Scope of benzimidazole-2-arylimine 3a–f.
Scheme 3
Scheme 3
Povarov reaction and rearrangement [49].
Scheme 4
Scheme 4
Substrate scope of dihydropyrimidines 5a–f.
Scheme 5
Scheme 5
Scope of the 4-(aryl)benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitriles 6a–f.
Figure 1
Figure 1
Molecular structure of 6c.
Scheme 6
Scheme 6
Plausible reaction mechanisms of dihydropyrimidines 5a–f formation and [1,3] sigmatropic rearrangement.
Figure 2
Figure 2
Absorption (a) and emission (b) spectra of fluorophores 6a–f in THF (c = 10−5 M).
Figure 3
Figure 3
Emission spectra of dyes 6a–f in powders (a) and photographs of the solid samples under daylight and 365 nm UV irradiation (b).
Figure 4
Figure 4
Emission spectra of dyes 6a–f in PVA films (a) and photographs of the samples under daylight and 365 nm UV irradiation (b).
Figure 5
Figure 5
Emission spectra of 6c in different ratios of THF–water (v/v) mixtures (a). Plot of I/I0 versus water fraction (vol%), where I0 is the fluorescence intensity in pure THF and emission images of the 6c in different water fraction mixtures under 365 nm UV illumination (λex = 365 nm) with the concentration of 10−5 M (b).
Figure 6
Figure 6
(a) Emission spectra of 6c in solid states (λex = 350 nm): as prepared (1), after grinding (2), and after treatment with CH2Cl2 (3). (b) Emission spectra of 6f in solid states (λex = 350 nm): as prepared (1), after grinding (2), and after treatment with CH2Cl2 (3).
Figure 7
Figure 7
Photographs of 6c (a) and 6f (b) taken under 365 nm UV irradiation.
Figure 8
Figure 8
Energy gaps of fluorophores 6a–f in THF phase.
Figure 9
Figure 9
Donor-acceptor structure 4-aryl-substituted benzo[4,5]imidazo[1,2-a]pyrimidine chromophors 6a–f.
Figure 10
Figure 10
The compound 6c in the thermal ellipsoid at the 50% probability level.
Figure 11
Figure 11
π-π-contacts in the crystal of the compound 6c.
See this image and copyright information in PMC

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