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

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 pi,pi* 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 similar to 1.5 eV. Saturated annulation enhances the PLQYs for complexes with primary pi,pi* 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.