title: Ultrafast energy transfer dynamics of a bioinspired dyad molecule.
abstract: A caroteno-purpurin dyad molecule was studied by steady-state and pump-probe spectroscopies to resolve the excited-state deactivation dynamics of the different energy levels as well as the connecting energy flow pathways and corresponding rate constants. The data were analyzed with a two-step multi-parameter global fitting procedure that makes use of an evolutionary algorithm. We found that following ultrafast excitation of the donor (carotenoid) chromophore to its S2 state, the energy flows via two channels: energy transfer (70%) and internal conversion (30%) with time constants of 54 and 110 fs, respectively. Additionally, some of the initial excitation is found to populate the hot ground state, revealing another limitation to the functional efficiency. At later times, a back transfer occurs from the purpurin to the carotenoid triplet state in nanosecond timescales. Details of the energy flow within the dyad as well as species associated spectra are disentangled for all excited-state and ground-state species for the first time. We also observe oscillations with the most pronounced peak on the Fourier transform spectrum having a frequency of 530 cm(-1). The dyad mimics the dynamics of the natural light-harvesting complex LH2 from Rhodopseudomonas acidophila and is hence a good model system to be used in studies aimed to further explain previous work in which the branching ratio between the competing pathways of energy loss and energy transfer could be manipulated by adaptive femtosecond pulse shaping.
authors.affiliation: FOM Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, The Netherlands. savolainen@amolf.nl
authors.forename: Janne
authors.initials: J
authors.lastname: Savolainen
authors.forename: Niels
authors.initials: N
authors.lastname: Dijkhuizen
authors.forename: Riccardo
authors.initials: R
authors.lastname: Fanciulli
authors.forename: Paul A
authors.initials: PA
authors.lastname: Liddell
authors.forename: Devens
authors.initials: D
authors.lastname: Gust
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Moore
authors.forename: Ana L
authors.initials: AL
authors.lastname: Moore
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hauer
authors.forename: Tiago
authors.initials: T
authors.lastname: Buckup
authors.forename: Marcus
authors.initials: M
authors.lastname: Motzkus
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Herek
mesh_terms: D000880:Anthraquinones / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D004735:Energy Transfer; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008958:Models, Molecular; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D019207:beta Carotene / Q000031:analogs & derivatives / Q000737:chemistry*
chemical_list: D000880:Anthraquinones; C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D019207:beta Carotene; C511975:purpurin anthraquinone