An Electron-Accepting aza-BODIPY-Based Donor-Acceptor-Donor Architecture for Bright NIR Emission.

Abstract

A bright near-infrared (NIR) fluorescent molecule was developed based on the donor-acceptor (D-A) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to elaborate a D-A-D structure caused redshifts of absorption and emission of PPAB into the NIR region with the enhanced fluorescence brightness up to 0.5\xa0×\xa0105\xa0M-1cm-1, whereas inserting a phenylene linker between the TPA donor and PPAB acceptor induced solvatochromic behaviors in emission. The transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D-A-D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7% and a low amplified spontaneous emission threshold of ca. 80\xa0μJ cm-2, indicating the high potential for NIR optoelectronic applications.