Insights into colour-tuning of chlorophyll optical response in green plants

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First-principles calculations within the framework of real-space time-dependent density functional theory have been performed for the complete chlorophyll (Chl) network of the light-harvesting complex from green plants, LHC-II. A local-dipole analysis method developed for this work has made possible the studies of the optical response of individual Chl molecules subjected to the influence of the remainder of the chromophore network. The spectra calculated using our real-space TDDFT method agree with previous suggestions that weak interaction with the protein microenvironment should produce only minor changes in the absorption spectrum of Chl chromophores in LHC-II. In addition, relative shifting of Chl absorption energies leads the stromal and lumenal sides of LHC-II to absorb in slightly different parts of the visible spectrum providing greater coverage of the available light frequencies. The site-specific alterations in Chl excitation energies support the existence of intrinsic energy transfer pathways within the LHC-II complex.
The authors acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374), European Commission Project CRONOS (grant number 280879-2, CRONOS CP-7P7), Spanish Grant (FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13 and IT395-10), UPV/EHU (grant UFI11/45), COST Actions CM1204 (XLIC) and MP1306 (EUSpec). JJS gratefully acknowledges the Comissionat per a Universitats i Recerca del Departament dInnovacio, Universitats i Empresa, de la Generalitat de Catalunya for financial support, and the Marie Curie Cofund Action (FP7) of the European Union for the Beatriu de Pinos (2010 BP-A2-00024) postdoctoral fellowship. JAR acknowledges the fellowship of the UPV/EHU. JJPS acknowledges financial support from the National Institute Of General Medical Sciences of the National Institutes of Health (Award Number 1R44GM108085-01A1). BFM acknowledges financial support from the Portuguese Foundation for Science and Technology (CONT_DOUT/11/UC/ 405/10150/18/2008), the Donostia International Physics centre and the Centro de Fisica de Materiales, UPV/EHU, for financial support.