Mohammad Kawsar Ahmed’s research while affiliated with Jagannath University and other places

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.

In this article, electric field modulated absorption (Stark absorption, SA) study of perylene doped in a poly (methyl methacrylate) (PMMA) polymer film at the concentrations of 1.0 mol%, 2.0 mol% and 3.0 mol% is presented. The field effects on the absorption spectra were found to originate mostly from the Stark shift induced by a change in molecular polarizability between the ground and excited states. The analyses of SA spectra with the aid of Liptay formalism yielded essentially the same magnitude of the average change in molecular polarizability (Δα), evaluated for the S0 -> S1 transition, for all the concentrations. This finding implies that Δα of perylene molecule doped in a PMMA film does not depend on concentration. Moreover, the yielded positive Δα for both the preparations implies that SA spectroscopy is an essential technique to probe spectroscopically that perylene possesses larger molecular polarizability in the excited states than in the ground state. Journal of Bangladesh Academy of Sciences, Vol. 43, No. 2, 133-139, 2019