We are very pleased to present this Festschrift in honor of our colleague, mentor and friend Prof. Volker Buß, which was initiated to celebrate his 75th birthday. The aim of this special issue is to recollect his substantial contributions and achievements of his career in the field of Theoretical/Computational Photochemistry. This article is protected by copyright. All rights reserved.

Ultrafast processes in light-absorbing proteins have been implicated in the primary step in the light-to-energy conversion and the initialization of photoresponsive biological functions. Theory and computations have played an instrumental role in understanding the molecular mechanism of such processes, as they provide a molecular-level insight of structural and electronic changes at ultrafast time scales that often are very difficult or impossible to obtain from experiments alone. Among theoretical strategies, the application of hybrid quantum mechanics and molecular mechanics (QM/MM) models is an important approach that has reached an evident degree of maturity, resulting in several important contributions to the field. This review presents an overview of state-of-the-art computational studies on subnanosecond events in rhodopsins, photoactive yellow proteins, phytochromes, and some other photoresponsive proteins where photoinduced double-bond isomerization occurs. The review also discusses current limitations that need to be solved in future developments.Ultrafast processes in light-absorbing proteins have been implicated in the primary step in the light-to-energy conversion and the initialization of photoresponsive biological functions. Theory and computations have played an instrumental role in understanding the molecular mechanism of such processes, as they provide a molecular-level insight of structural and electronic changes at ultrafast time scales that often are very difficult or impossible to obtain from experiments alone. Among theoretical strategies, the application of hybrid quantum mechanics and molecular mechanics (QM/MM) models is an important approach that has reached an evident degree of maturity, resulting in several important contributions to the field. This review presents an overview of state-of-the-art computational studies on subnanosecond events in rhodopsins, photoactive yellow proteins, phytochromes, and some other photoresponsive proteins where photoinduced double-bond isomerization occurs. The review also discusses current limitations that need to be solved in future developments.

Reversible storage of hydrogen in the form of stable and relatively harmless chemical substances such as formic acid (FA) is one of the cornerstones of a fossil-fuel-free economy. Recently, Ru(III)-PC(sp3)P (where PC(sp3)P = modular dibenzobarrelene-based pincer ligand possessing a pendant functional group) complex 1 has been reported as a mild and E-selective catalyst in semihydrogenation of alkynes with stoichiometric neat formic acid. Discovery of the additive-free protocol for dehydrogenation of FA launched further studies aiming at the rational design of highly efficient catalysts for this reaction operating under neutral conditions. We now report the results of our investigation on a series of bifunctionl PC(sp3)P complexes equipped with different outer-sphere auxiliaries, that allowed us to identify an amine-functionalized Ir(III)-PC(sp3)P complex 3, as a clean and efficient catalyst for the FA dehydrogenation. The catalyst is suitable for fuel-cell applications demonstrating a TON up to 5 × 105 and TOF up to 2 × 104 h–1 (3.8 × 105 and 1.2 × 104 h–1 with no additives). In addition to the practical value of the catalyst, experimental and computational mechanistic studies provide rationale for the design of improved next-generation catalysts.Reversible storage of hydrogen in the form of stable and relatively harmless chemical substances such as formic acid (FA) is one of the cornerstones of a fossil-fuel-free economy. Recently, Ru(III)-PC(sp3)P (where PC(sp3)P = modular dibenzobarrelene-based pincer ligand possessing a pendant functional group) complex 1 has been reported as a mild and E-selective catalyst in semihydrogenation of alkynes with stoichiometric neat formic acid. Discovery of the additive-free protocol for dehydrogenation of FA launched further studies aiming at the rational design of highly efficient catalysts for this reaction operating under neutral conditions. We now report the results of our investigation on a series of bifunctionl PC(sp3)P complexes equipped with different outer-sphere auxiliaries, that allowed us to identify an amine-functionalized Ir(III)-PC(sp3)P complex 3, as a clean and efficient catalyst for the FA dehydrogenation. The catalyst is suitable for fuel-cell applications demonstrating a TON up to 5 × 105 and TOF up to 2 × 104 h–1 (3.8 × 105 and 1.2 × 104 h–1 with no additives). In addition to the practical value of the catalyst, experimental and computational mechanistic studies provide rationale for the design of improved next-generation catalysts.