Energy transfer in light-harvesting antenna complexes probed by two-dimensional spectroscopy

Petar H. Lambreva,b, Parveen Akhtara,b, Győző Garaba, Cheng Zhangb, Nhut Do Thanhb, Howe-Siang Tanb
aHungarian Academy of Sciences, Biological Research Centre, Temesvári krt. 62, Szeged, Hungary; bNanyang Technological University, School of Physical and Biological Sciences, Nanyang Link 21, 637371 Singapore

Excitation energy transfer (EET) in the harvesting antenna complexes, such as the plant light-harvesting complex II (LHCII), is a key determinant of the overall photosynthetic efficiency [1, 2]. Disentangling the EET processes in LHCII and similar multichromophore systems ­­– characterised by high spectral congestion, dynamic flexibility (disorder) and many intra- and intercomplex chromophore interactions – is a challenging experimental task. Two-dimensional electronic spectroscopy (2DES) has established itself as a powerful experimental approach capable of resolving the excitation dynamics with high spectral and temporal resolution. Recently we have applied room-temperature 2DES to probe the EET between chlorophyll (Chl) b and Chl a in detergent-solubilized LHCII trimers and detergent-free aggregates [3, 4].

While we found no discernible differences in the kinetics of Chl b to Chl a EET, the results suggested a change in the dynamics of exciton relaxation in the Chl a domain. Here we report on a follow-up study focused on the latter. We were able to record purely absorptive 2D spectral dynamics free from singlet-singlet annihilation. By using low-energy excitation pulses covering the entire Chl a Qy region, we were able to, for the first time, experimentally resolve downhill and uphill exciton equilibration and kinetics of spectral diffusion due to dynamic disorder in LHCII and other light-harvesting systems, unravelling new details about the processes of light harvesting. Furthermore, the results clearly show that the EET dynamics in LHCII is influenced by its molecular surrounding.

References

[1]        R. Croce, H. van Amerongen, Nat Chem Biol, 2014, 10, 492–501.
[2]        H. van Amerongen, R. Croce, Photosynth Res, 2013, 116, 251–263.
[3]        K. Wells, P. H. Lambrev et al., Phys Chem Chem Phys, 2014, 11640–11646.
[4]        M. G. M. Enriquez, P. Akhtar et al., J Chem Phys, 2015, 142, 212432.