Exploiting N-H-pi Interactions in 2-(dimesitylboraneyl)-1H-pyrrole for Luminescence Enhancement

Design and development of stable blue emitters are challenging owing to their potential applications in displays and lighting technologies. Triarylborane (TAB) with suitable donors has been extensively exploited in several fields. We report herein the synthesis and structural characterization of a simple 2-(dimesitylboryl)-1H-pyrrole (2) and its precursor N-Boc-(dimesitylboryl)-pyrrole (1). In the crystal lattice of 2, supramolecular dimer was formed by strong N-H-pi (2.59 angstrom) hydrogen bonding interactions between the monomers and this dimer is further connected by weak van der Waals interactions (C-H-pi) with neighbouring dimers to form a supramolecular network. There is no solvatochromism noted in the absorption spectra, however significant positive solvatochromism was observed in the fluorescence spectra; points to the polar nature of excited state of 1 and 2. Compound 2 showed intense and efficient blue color luminescence in the solid state than that of 1. Thus, N-H-pi interactions and pi-excessive nature of pyrrole are responsible for the above features. Impressively, compounds 1 and 2 exhibit the phosphorescence emission with a long-lived lifetime of similar to 0.55 s at 77 K and delayed fluorescence at room temperature. DFT/TD-DFT calculations were performed to support the experimental observations.