Polarity-dependent solvatochromic properties of thermally activated delayed fluorescence with donor–acceptor constituents under different excitation energies

Abstract

A novel solvatochromic fluorescent molecule, i.e., DpAn–InAc, is reported and synthesized using a palladium-catalyzed Buchwald–Hartwig cross-coupling process. DpAn–InAc exhibits thermally activated delayed fluorescence character. It has a twisting donor–acceptor configuration, which contributes to interesting solvatochromic properties when changing the excitation energy and the orientational polarizability of the solvent. Fluorescent solvatochromic experiments for DpAn–InAc solutions show a red shift of 90 nm from 540 nm in toluene to 630 nm in tetrahydrofuran. The photoluminescence spectrum of DpAn–InAc in chloroform solution of medium polarity shows dual emission peaks at 450 nm and 550 nm, originating from low-lying local excited (LE) and charge-transfer (CT) states, respectively. When decreasing the excitation energy gradually, it is found that the main excited state of DpAn–InAc changes from the CT state to the LE state. DpAn–InAc has great potential in applications including fluorescent probes and fluorescent sensors.