Upon selective 355 nm excitation of 4a 2+ and efficient quenching by BP, we unambiguously identified BP •+ in the TA spectra through its characteristic absorption band in the red spectral region (lower part of Figure ). A spectral separation with the literature-known BP •+ spectrum clearly indicates that the quenching by-product, 4a •+ , has an absorption band between 500 and 650 nm. The observed ground-state bleach (GSB) between ~410 and ~480 nm reveals that 4a 2+