Triplet excited state properties. Nanosecond transient absorption (TA) spectroscopy was employed to explore the triplet excited states and the proposed non-radiative pathways of the AL(DIPY)3 chelates (SI S3.5). A relative estimation of the triplet state quantum yield between the complexes was made. The desired long-lived triplet excited states were observed, and the triplet excited lifetimes (τT) were defined in air equilibrated solutions by simple monoexponential fitting. TA spectra were recorded in non-polar toluene solution and polar ethanolic solution.