Impact of Electron-Donating Groups on Attaining Dual-Emitting Imidazole-Based Donor–Acceptor Materials

Imidazole-based donor–acceptor materials are well known for their polarity-controlled trade-off phenomenon between the localized excitation-based short-wavelength (SW) emission in nonpolar solvents and charge transfer dominated long-wavelength (LW) emission in polar solvents. To attain concurrent SW- and LW-based dual-emission characteristics, a series of imidazole-based donor–acceptor fluorophores (CBImDCN, TPImDCN, PZImDCN) possessing different electron-donating groups such as carbazole, triphenylamine, and phenothiazine linked via the N-position of the imidazole core unit were synthesized and verified by NMR and mass spectroscopic techniques. As a result, the strong donating TPImDCN and PZImDCN exhibited dual emission in different solvents of varying polarity, covering the blue (SW) and green/orange (LW) regions. On the other hand, in contrast, only an SW emission band is observed with the weak donating CBImDCN. Moreover, PZImDCN shows panchromatic emission under 365 nm illumination, while only orange color emission is observed under visible light excitation, revealing two different origins of SW and LW emissions, as also evidenced from DFT calculations. Overall, this work reveals a new approach for attaining concurrent SW and LW emission characteristics from imidazole-based D–A materials and sheds light on the design and development of novel panchromatic emitters with intriguing properties for lighting and display applications.