Photosynthetic organisms employ antenna arrays composed of many chromophore molecules to capture solar energy and funnel it into photosynthetic reaction centers.  This energy is used to generate electrochemical potential in the form of a pH gradient across the photosynthetic membrane.  As the intensity of incident light increases, the pH on the lumenal side of this membrane decreases.  Under strong light conditions there is considerably more solar energy being absorbed than the photosynthetic apparatus can utilize.  Unchecked, this would lead to a build up of reactive and potentially harmful redox intermediates within the apparatus.  A photoprotective mechanism, nonphotochemical quenching (NPQ), is activated as the pH in the lumen decreases and harmlessly dissipates the excess absorbed energy as heat.  Due to the inherent complexity of natural systems, the fundamental mechanistic details of NPQ are not well understood.  By studying synthetic analogs we hope to gain insight into the photophysics and photochemistry of NPQ.  These artificial systems may also serve as a framework for incorporating photoprotection into organic solar energy devices.We have designed and synthesized compounds to mimic various aspects of NPQ for photophysical characterization. Our studies of an antenna analog, Hexad, demonstrated the capacity for a pH-sensitive rhodamine dye, R, to rapidly quench zinc porphyrin excited states in an acidified solution1.  A reaction center model, Triad, should be able to generate a long-lived charge separated state via photoinduced electron transfer from the excited state of a zinc porphyrin to a functionalized fullerene under neutral conditions.  Acidified solutions of Triad are expected to exhibit reduced quantum yields of this charge separated state as excitation energy will be largely dissipated by R. 1. Terazono, Y.; et al. Journal of the American Chemical Society, 2011 , 133 (9), 2916-2922.

Mimicking photoprotection in a model photosynthetic reaction center

247th National Meeting (2014)

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