Excited State Properties of Fucoxanthin Aggregates

The structure and excited state properties of the H- and J-aggregates of the marine carbonyl carotenoid, fucoxanthin(Fx), were studied by various spectroscopic methods, and compared with those of Fx monomers in polar organic solvents. The fluorescent analysis indicated that the higher vibronic states of S2 contribute more to populating the S1 state, from which fluorescent emission mainly originates. Resonance Raman and density functional theory calculations confirmed the ‘card-packed’ and ‘head-to-tail’ structures of the H- and J-aggregates of Fx, respectively. An fs time-resolved absorption study proved the coexistence of S1 and intramolecular charge transfer relaxation pathways upon excitation to the S2 state for both the monomers and aggregates.