Jelena Dodonova

Functionalization of pyrrolo[2,3-d]pyrimidine by palladium-catalyzed cross-coupling reactions (review)

Palladium-catalyzed cross-coupling reactions (Heck, Sonogashira, Stille, Suzuki) in the pyrrolo-[2,3-d]pyrimidine series with emphasis on synthesis of biologically active and functional materials are reviewed.

2,4-Bis(4-aryl-1,2,3-triazol-1-yl)pyrrolo[2,3-d]pyrimidines: synthesis and tuning of optical properties by polar substituents

2,4-Bis(4-aryl-1,2,3-triazol-1-yl)pyrrolo[2,3-d]pyrimidines as D–π–A–π–D chromophores were successfully prepared by CuAAC reaction of 2,4-diazido-7-methylpyrrolo[2,3-d]pyrimidine with ethynylarenes in dichloromethane in the presence CuI/DIPEA/AcOH as a catalyst system. The incorporation of small polar substituents enabled tuning of the energy of frontier orbitals and thus the FMOs energy gap by up to 0.9 eV, while the incorporation of bulky steric substituents resulted in narrowing of the energy gap by up to 0.4 eV. Owing to electron-accepting properties of pyrrolo[2,3-d]pyrimidine core extending to triazole moieties the compounds with electron-donating groups showed expressed intramolecular charge transfer character (ICT) of the excited states which was proved by solvatochromic dynamics and supported by DFT calculations. The optimization of ICT reduced radiative and non-radiative deactivation pathways resulted in enhancement of fluorescence quantum yield up to 73%.

Access to 6-arylpyrrolo[2,3-d]pyrimidines via a palladium-catalyzed direct C–H arylation reaction

An efficient method of palladium-catalyzed direct arylation has been developed for the selective functionalization of the C6 position of 2,4-diarylpyrrolo[2,3-d]pyrimidines. Under optimal conditions, various aryl bromides successfully provided a wide range of 6-arylpyrrolo[2,3-d]pyrimidines.

Room temperature phosphorescence vs thermally activated delayed fluorescence in carbazole – pyrimidine cored compounds

Utilization of “dark” triplet states is a key task for design of novel emissive organic compounds. Thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) are two promising pathways to employ triplet excitons and reach high internal quantum efficiencies. In this paper we present a series of carbazole–pyrimidine cored compounds, showing RTP and TADF. A specific energy level scheme was shown to promote intersystem crossing and RTP in carbazole–pyrimidine derivatives with phosphorescence quantum yield values of up to 0.07 in rigid Zeonex films. The modification of the acceptor core with 2-methylthio and dimethylamine fragments allowed us to reduce the singlet–triplet energy gap, enhance the rISC (reverse intersystem crossing) rate and obtain high intensity TADF with a fluorescence quantum yield of up to 0.32. Time resolved fluorescence analysis revealed the presence of conformational disorder of the donor–acceptor core governing TADF properties in solid films. A method to control the conformational disorder by enhancing the host rigidity was demonstrated. Sky-blue electroluminescence was shown for the dimethylamino-modified compound with the most intense TADF. Our results show that carbazole–pyrimidine cored materials are versatile donor–acceptor systems for achieving RTP and TADF via simple structural modifications.