Recently, we used a local orbital density functional theory code called FIREBALL, to study the photoisomerization process in azobenzene derivatives for solar energy materials. Azobenzene functional groups undergo photoisomerization upon light irradiation or application of heat. Zhou et al (2012 J. Am. Chem. Soc. 134 99-102) showed that these azobenzenes can then be introduced into metal-organic frameworks via an organic linker in order to create a reversible switch for CO2 adsorption. In this manuscript, we examined how the addition of organic linkers (isophthalic acid) changes the relaxation times, isomerization mechanism, and quantum yield for both the cis↔trans pathways. We then tuned these properties by substituting functional groups, finding an increase in quantum yield as well as improved optical properties.
We report non-adiabatic molecular dynamic simulations of the ring opening reaction of diarylethene (DAE) derivative molecules, both free standing and embedded between gold electrodes. Simulations are performed by the surface hopping method employing density functional theory. Typically, the free-standing molecules exhibit large quantum yields to open and close; however the process is quenched for the molecules embedded between electrodes. Our simulations reveal the importance of the DAE side chemical groups, which explain the efficiency of the quenching process. Namely, delocalization of the LUMO state contributes to electronic coupling between the molecule and electrodes, suppressing or enhancing the reaction process. The simulations indicate that a proper choice of the chemical side group, which provides the strong localization of the LUMO state, can substantially diminish the quenching mechanism. Additionally, we analyze a strong dependency of the quantum yield of the opening reaction coming from the mechanical strength of the molecules.
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