Fig. 8: General scheme for electrostatic-induced spectral tuning and excited state decay control in retinal systems. | Nature Communications

Fig. 8: General scheme for electrostatic-induced spectral tuning and excited state decay control in retinal systems.

From: Retinal photoisomerization versus counterion protonation in light and dark-adapted bacteriorhodopsin and its primary photoproduct

Fig. 8

A Well-separated S1/S2 and S0/S1 energy gaps eliminates electronic mixing-induced barriers along the S1 decay path, thus facilitating a fast and efficient decay and photoisomerization (this is what happens in the new BR counterion model presented here, Rhodopsin18,37,48,84 and the gas phase18). B Blue shift and strong S1/S2 (ionic/covalent) mixing (as it happens in solvents17 or in BR when adopting the standard quadrupole counterion model) resulting in a S1/S2 mixing-induced barrier along the photoisomerization paths that slows down decay. C Red shift and strong S1/S0 mixing (BR at low pH, giving a protonated ASP85)81, resulting in a S0/S1 mixing-induced barrier also slowing down decay and photoisomerization (the heavily red shifted, to 690 nm, Neorhodopsin being the extreme case, showing intense fluorescence with no photoisomerization)70. ABL and EBL points refer to alternate bond lengths and equalized bond lengths, respectively.

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