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.