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 pyrazolyl dibenzofuran and dipyrazolyl carbazole units. Through a detailed electrochemical, theoretical and optical studies. The synthesis involves the Ullmann-type amination of the corresponding dibromo-dibenzo heteroarene with commercially available pyrazole unit. The selective electrophilic bromination at the 4th position of the pyrazole unit of 2,8-dipyrazolyl dibenzofuran have been achieved, and 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 low energy absorption bands of each luminogens upon incorporation of the arene on pyrazole subunit. Steady state emission studies at room temperature and low temperature (77 K) exhibits indication of TADF features of the synthesized chromophores, revealing the potential future optical applications like third generation TADF based organic light emitting diode fabrication opportunity. Electrochemical and theoretical investigations of the synthesized materials are also included for the 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.