Astaxanthin forms three types of aggregates in hydrated dimethyl sulfoxide (DMSO). In DMSO/water ratio of 1:1, a red-shifted J-aggregate with maximum at 570 nm is generated, while a ratio of 1:9 produces blue-shifted H-aggregates with peaks at 386 nm (H1) and 460 nm (H2). Monomeric astaxanthin in DMSO has an S-1 lifetime of 5.3 ps, but a long-lived (33 ps) S* signal was also identified. Aggregation changes the S-1 lifetimes to 17 Ps (H1), 30 Ps (H2), and 14 ps (J). Triplet state of astaxanthin, most likely generated via singlet homofission, was observed in H1 and H2 aggregates. (C) 2013 Elsevier B.V. All rights reserved.