4-Arylpyrazole-decorated dibenzofuran: synthesis, characterization, optical studies and computational analysis

Abstract

In this work, we report the design and synthesis of U-shaped molecules based on 4-arylpyrazolyl dibenzofuran and dipyrazolyl carbazole units. Through detailed electrochemical, theoretical and optical studies, we establish thermally activated delayed fluorescence (TADF) in these molecules. The synthesis involves the Ullmann-type amination of the corresponding dibromo–dibenzo heteroarene with the commercially available pyrazole unit. The selective electrophilic bromination at the 4th position of the pyrazole unit of 2,8-dipyrazolyl dibenzofuran has been achieved, and it subsequently underwent the Suzuki–Miyaura reaction with arylboronic acids and furnished the extended conjugated molecules 4-arylpyrazole-dibenzofurans. UV-vis absorption studies show the bathochromic shift of the low-energy absorption bands of each luminogen upon the incorporation of the arene on the pyrazole subunit. Steady-state emission studies at room temperature and low temperature (77 K) exhibit the TADF features of the synthesized chromophores, revealing their potential future optical applications, like the third-generation TADF-based organic light-emitting diode fabrication opportunity. Electrochemical and theoretical investigations of the synthesized materials are also included for further support regarding the observed optical features. Theoretical calculations indicate localized LUMOs, delocalized HOMOs and as a result small singlet–triplet energy gaps, providing support to the chemiluminescence studies that established TADF in these molecules.