Absence of far red emission band in aggregated core antenna complexes

Abstract Reported herein is a Stark fluorescence (SF) spectroscopy study performed on photosystem II core antenna complexes CP43 and CP47 in their native and aggregated states. The systematic mathematical modeling of the SF spectra with the aid of conventional Liptay formalism revealed that induction of aggregation in both the core antenna complexes via detergent removal results in a single quenched species characterized by a remarkably broad and inhomogenously broadened emission lineshape peaking around 700 nm. The quenched species possesses a fairly large magnitude of charge-transfer (CT) character. From the analogy with the results from aggregated peripheral antenna complexes, the quenched species is thought to originate from the enhanced chlorophyll-chlorophyll (Chl-Chl) interaction due to aggregation. However, in contrast, aggregation of both core antenna complexes did not produce a far-red emission band at about 730 nm, which was identified in most of the aggregated peripheral antenna complexes [Wahadoszamen et al, PCCP 2012, Wahadoszamen et al BBA 2016]. The 730 nm emission band of the aggregated peripheral antenna complexes was attributed to the enhanced chlorophyll - carotenoid (lutein1) interaction in the terminal emitter locus. Therefore, it is very likely that the no occurrence of the far-red band in the aggregated core antenna complexes is directly related to the absence of lutein1 in their structures. The absence of the far-red band also suggests the possibility that aggregation induced conformational change of the core antenna complexes does not yield a chlorophyll-carotenoid (Chl-Car) interaction associated energy dissipation channel.