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The color of rhodopsins is regulated by the interaction of the chromophore with its counterion. Here the authors introduce a computational model showing that color tuning can be described in terms of virtual counterion migration and delocalization pathways.

The control of reaction quantum efficiencies is a fundamental photochemical problem. Here the authors use comparative quantum-classical dynamics to reveal that the synchronization of specific vibrations with the reaction coordinate is a key promoting factor.

Improving the efficiency of light-driven molecular rotary motors is a challenging task. Here, the authors combine theoretical modeling, synthesis and spectroscopy to prepare a prototype molecular motor capable of avoiding inefficient thermally activated motion; thus offering prospects to implement a 2-stroke photon-only molecular motor.

Fluorescent proteins that self-assemble and localize in the neuron membrane are vital in neurosciences, particularly in optogenetics applications. Here the authors present a quantum-mechanics/molecular mechanics model for the photoisomerization of the natural highly fluorescent Neorhodopsin, explaining the highly fluorescent quantum yield that could lead to effective visualization of neural signals.

Arch-3 rhodopsin variants are common fluorescent reporters of neuronal activity. Here, the authors show with quantum chemical modelling that a set of these proteins reveals a direct proportionality between their observed fluorescence intensity and the stability of an exotic excited-state diradical intermediate.

Microbial rhodopsins are photoreceptive and widely used in optogenetics for which they should preferable function with longer-wavelength light. Here, authors achieve a 40-nm red-shift in the absorption wavelength of a sodium-pump rhodopsin (KR2) by altering the distribution of the retinal chromophore.

Isotope effects provide deep insight into mechanisms of chemical and biochemical processes. Now, it has been shown that the pattern of isotopic substitution of the isomerizing bond of the retinal chromophore in the visual pigment rhodopsin significantly alters the reaction quantum yield—revealing a vibrational phase-dependent isotope effect.

Rhodopsin activation is driven by an ultrafast double-bond isomerization, but questions remain about the origin of its sensitivity. Now, quantum–classical simulations show that, 15 fs after light absorption, a degeneracy between the reactive excited state and a neighbouring state causes the splitting of the rhodopsin population into subpopulations, which propagate with different velocities, leading to distinct contributions to the quantum efficiency.

The ultrafast, vibrationally coherent photoisomerization of rhodopsin is a model of efficient photomechanical energy conversion at the molecular scale. Here, the authors demonstrate a similar photoreaction in synthetic compounds, unraveling the underlying mechanism and discussing its implications.

Increasing the rotational efficiency of single-molecule light-driven rotary motors often relies on chemical modifications aimed at eliminating the factors that hinder rotation. Using multiscale nonadiabatic simulations, the authors investigate the transient conformations assumed by the motor molecule during its operation in a solvent and examine possibilities for enhancing the motor’s efficiency by blocking certain solvent-solute interactions that restrain successful completion of the rotational movement.

Nakajima, Pedraza-González et al. provide a comprehensive investigation of amino acid mutations at position 219 of the sodium pump rhodopsin, KR2, and their role in the color tuning of the retinal chromophore. They prepared P219X (X= A, C, D, E, F, G, H, I, K, L, M, N, Q, R, S, T, V, W, Y) mutants of KR2, and find that all mutants are red-shifted, except for P219R, highlighting its role as a color determinant in the light-driven pump KR2.