title: Emission lineshapes of the B850 band of light-harvesting 2 (LH2) complex in purple bacteria: a second order time-nonlocal quantum master equation approach.
abstract: The emission lineshape of the B850 band in the light harvesting complex 2 of purple bacteria is calculated by extending the approach of 2nd order time-nonlocal quantum master equation [S. Jang and R. J. Silbey, J. Chem. Phys. 118, 9312 (2003)]. The initial condition for the emission process corresponds to the stationary excited state density where exciton states are entangled with the bath modes in equilibrium. This exciton-bath coupling, which is not diagonal in either site excitation or exciton basis, results in a new inhomogeneous term that is absent in the expression for the absorption lineshape. Careful treatment of all the 2nd order terms are made, and explicit expressions are derived for both full 2nd order lineshape expression and the one based on secular approximation that neglects off-diagonal components in the exciton basis. Numerical results are presented for a few representative cases of disorder and temperature. Comparison of emission line shape with the absorption line shape is also made. It is shown that the inhomogeneous term coming from the entanglement of the system and bath degrees of freedom makes significant contributions to the lineshape. It is also found that the perturbative nature of the theory can result in negative portion of lineshape in some situations, which can be removed significantly by inclusion of the inhomogeneous term and completely by using the secular approximation. Comparison of the emission and absorption lineshapes at different temperatures demonstrates the role of thermal population of different exciton states and exciton-phonon couplings.
authors.affiliation: Department of Chemistry and Biochemistry, Queens College of the City University of New York, 65-30 Kissena Boulevard, Flushing, New York 11367, USA.
authors.forename: Praveen
authors.initials: P
authors.lastname: Kumar
authors.forename: Seogjoo
authors.initials: S
authors.lastname: Jang
mesh_terms: D000465:Algorithms; D001426:Bacterial Proteins / Q000737:chemistry*; D003198:Computer Simulation; D004735:Energy Transfer; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008956:Models, Chemical; D020560:Proteobacteria / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes