TY - JOUR
T1 - Q(y) and Q(x) Absorption Bands for Bacteriochlorophyll a Molecules from LH2 and LH3
AU - Anda, Andre
AU - Hansen, Thorsten
AU - De Vico, Luca
PY - 2019/6/27
Y1 - 2019/6/27
N2 - Light-harvesting systems 2 and 3 (LH2 and LH3) act as antennas for the initial light capture by photosynthetic purple bacteria, thus initiating the conversion of solar energy into chemical energy. The main absorbers are carotenoids and bacteriochlorophylls (BChls), which harvest different parts of the solar spectrum. The first two optical transitions in BChl produce the Qy and Qx absorption bands. The large size of BChl molecules has prevented accurate computational determination of the electronic structures for the relevant states, until we recently succeeded in obtaining the excitation energies and transition dipole moments of the first (Qy) transition for all BChls in LH2 and LH3 using multi-state multiconfigurational second-order perturbation theory calculations. In this work, we go one step further, compute the corresponding values for the Qx transition, in line with previous work [ J. Am. Chem. Soc. 2017, 139, 7558-7567 ], and compare and assess our data against excitation energies obtained through time-dependent density functional theory methods. Interestingly, we find that the two transitions respond differently to BChls' geometrical factors, such as the macrocycle ring curvature and the dihedral torsion of the acetyl moiety. These findings will aid the unraveling of structure-function relationships for absorption and energy transfer processes in purple bacteria, and once again this demonstrates the viability of multireference quantum chemical methods as computational tools for the photophysics of biomolecules.
AB - Light-harvesting systems 2 and 3 (LH2 and LH3) act as antennas for the initial light capture by photosynthetic purple bacteria, thus initiating the conversion of solar energy into chemical energy. The main absorbers are carotenoids and bacteriochlorophylls (BChls), which harvest different parts of the solar spectrum. The first two optical transitions in BChl produce the Qy and Qx absorption bands. The large size of BChl molecules has prevented accurate computational determination of the electronic structures for the relevant states, until we recently succeeded in obtaining the excitation energies and transition dipole moments of the first (Qy) transition for all BChls in LH2 and LH3 using multi-state multiconfigurational second-order perturbation theory calculations. In this work, we go one step further, compute the corresponding values for the Qx transition, in line with previous work [ J. Am. Chem. Soc. 2017, 139, 7558-7567 ], and compare and assess our data against excitation energies obtained through time-dependent density functional theory methods. Interestingly, we find that the two transitions respond differently to BChls' geometrical factors, such as the macrocycle ring curvature and the dihedral torsion of the acetyl moiety. These findings will aid the unraveling of structure-function relationships for absorption and energy transfer processes in purple bacteria, and once again this demonstrates the viability of multireference quantum chemical methods as computational tools for the photophysics of biomolecules.
U2 - 10.1021/acs.jpca.9b02877
DO - 10.1021/acs.jpca.9b02877
M3 - Journal article
C2 - 31242736
SN - 1089-5639
VL - 123
SP - 5283
EP - 5292
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 25
ER -