Improving Near-Infrared Emission of meso-Aryldipyrrin Indium(III) Complexes via Annulation Bridging: Excited-State Dynamics

Abstract

Using non-adiabatic dynamics and Redfield theory, we predicted the optical spectra, radiative and nonradiative decay rates, and photoluminescence quantum yields (PLQYs) for In­(III) dipyrrin-based complexes (i) with electron-withdrawing (EW) or electron-donating (ED) substituents on the meso-phenyl group and (ii) upon fusing the pyrrin and phenyl rings via saturated or unsaturated bridging to increase structural rigidity. The ED groups lead to a primary π,π* character with a minor intraligand charge transfer (ILCT) contribution to the emissive state, while EW groups increase the ILCT contribution and red-shift the luminescence to ∼1.5 eV. Saturated annulation enhances the PLQYs for complexes with primary π,π* character compared to those of the non-annulated and unsaturated–annulated complexes, while both unsaturated and saturated annulation decrease the PLQYs for complexes with primary ILCT character. We found that PLQY improvement goes beyond a simple concept of structural rigidity. In contrast, the charge transfer character of excitonic states is a key parameter for engineering the NIR emission of In­(III) dipyrrin complexes.

Combined Machine Learning, Computational, and Experimental Analysis of the Iridium(III) Complexes with Red to Near-Infrared Emission

“…11,21 Depending on the benzannulation site on the N^N ligand, the Ir(III) complexes can exhibit a blue-or redshift of the lowest-energy absorption and emission bands. 22 This is attributed to the site-dependent destabilization or stabilization of the excited electron state upon benzannulation on the N^N ligand of the Ir(III) complexes, 23 while benzannulation on the C^N ligands either decreased the emission energy or had a negligible effect on the emission energy depending on the site of benzannulation. 11 Despite these abundant experimental and computational studies of the optical properties of Ir(III) complexes, 13,20,21,33 establishing the relationship between the structures of the ligands and the emission properties of the Ir(III) complexes for a rational design of complexes with desired emission properties is still a complicated task due to scarce and insufficient experimental publicly available data.…”

“…Extending π-conjugation can also be achieved via benzannulation on the N^N or C^N ligands of the Ir­(III) complexes. , Depending on the benzannulation site on the N^N ligand, the Ir­(III) complexes can exhibit a blue- or red-shift of the lowest-energy absorption and emission bands . This is attributed to the site-dependent destabilization or stabilization of the excited electron state upon benzannulation on the N^N ligand of the Ir­(III) complexes, while benzannulation on the C^N ligands either decreased the emission energy or had a negligible effect on the emission energy depending on the site of benzannulation …”