Under excess illumination, photosystem II of oxygenic photosynthesis dissipates excess energy through the quenching of chlorophyll fluorescence, a process known as non-photochemical quenching (NPQ). This rapidly reversible photoprotective mechanism is vital for oxygenic photosynthetic organisms to cope with varying light conditions. Activation of NPQ has been linked to the conversion of a carotenoid with a conjugation length of 9 double bonds (violaxanthin) into an 11 double-bond carotenoid (zeaxanthin). Recently, we have mimicked NPQ in an artificial dyad model systems comprising a phthalocyanine covalently linked to a carotenoid of various conjugation lengths (Berera et al., PNAS 103, 2006, 5343-5348). Remarkably, the addition of only one double bond can turn the carotenoid from a non-quencher into a very strong quencher of the phthalocyanine singlet excited state. By applying femtosecond transient absorption spectroscopy it was shown that the quenching proceeds through energy transfer from the excited phthalocyanine to the optically forbidden S1 state of the carotenoid, coupled to an intramolecular charge-transfer state. Here, we further investigate the quenching capabilities and quenching mechanisms of caroteno-tetrapyrrole dyads by varying physical-chemical parameters such as the nature of the covalent linkage, the linker length, substitutions on the carotenoid backbone and redox potential of the tetrapyrrole. These studies may aid in the development of photoprotective feedback mechanisms in artificial photosynthetic devices.