posted on 2021-09-28, 11:34authored byWan Xu, Levi Lystrom, Yanxiong Pan, Xinyang Sun, Salim A. Thomas, Svetlana V. Kilina, Zhongyu Yang, Hua Wang, Erik K. Hobbie, Wenfang Sun
The
synthesis and photophysics (UV–vis absorption, emission,
and transient absorption) of four neutral heteroleptic cyclometalated
iridium(III) complexes (Ir-1–Ir-4) incorporating thiophene/selenophene-diketopyrrolopyrrole (DPP)-substituted
N-heterocyclic carbene (NHC) ancillary ligands are reported. The effects
of thiophene versus selenophene substitution on DPP and bis- versus
monoiridium(III) complexation on the photophysics of these complexes
were systematically investigated via spectroscopic techniques and
density functional theory calculations. All complexes exhibited strong
vibronically resolved absorption in the regions of 500–700
nm and fluorescence at 600–770 nm, and both are predominantly
originated from the DPP-NHC ligand. Complexation induced a pronounced
red shift of this low-energy absorption band and the fluorescence
band with respect to their corresponding ligands due to the improved
planarity and extended π-conjugation in the DPP-NHC ligand.
Replacing the thiophene units by selenophenes and/or biscomplexation
led to the red-shifted absorption and fluorescence spectra, accompanied
by the reduced fluorescence lifetime and quantum yield and enhanced
population of the triplet excited states, as reflected by the stronger
triplet excited-state absorption and singlet oxygen generation.