Photoinduced electron transfer from zinc meso-tetraphenylporphyrin to a one-dimensional perylenediimide aggregate: Probing anion delocalization effects

Organic photovoltaics incorporating non-fullerene acceptors based on perylenediimide (PDI) now rival fullerene acceptor-based devices in performance, although the mechanisms of charge generation in PDI-based devices are not yet fully understood. Fullerene-based systems are proposed to undergo electron transfer directly from the photoexcited donor into a band of delocalized acceptor states, thus increasing charge generation efficiency. Similarly, anion delocalization has been shown to enhance the rate of electron transfer from a photoexcited donor to two electronically coupled PDI acceptors. Here we investigate how additional electron acceptors may further increase the rate of electron transfer from the donor zinc meso-tetraphenylporphyrin (ZnTPP) to an aggregate of PDI acceptors (PDI[Formula: see text]. Femtosecond transient visible and mid-infrared absorption spectroscopies show that the rate of electron transfer from 1*ZnTPP to the PDI assembly ZnTPP2-PDI3 is statistically identical to that of the previously examined ZnTPP-PDI2. A Marcus theory analysis indicates that the parameters governing electron transfer are nearly identical for the two molecules, suggesting that the maximum electron transfer rate enhancement has been achieved in a cofacial PDI dimer because the ZnTPP directly couples to the first two PDI acceptors whereas the coupling to the third PDI is too weak.

Quantum vs Thermal Effects in Formic Acid Adsorption on (101) TiO2 Anatase Surfaces

<p>Carboxylic acids adsorption on anatase TiO₂ is a key process in circular economy and sustainability. Yet, in spite of several decades of investigations, its intimate working mechanisms still remain elusive. In particular, the behavior of the acid proton and its localization – either on the molecule or on the surface – are still open issues. By modeling the adsorption of formic acid on top of regular (101) anatase TiO₂ surfaces, we found that, in the 0 K limit, the acid proton is shared between a carboxylic oxygen and a surface oxygen. In this regime, the proton behavior is mainly governed by quantum delocalization effects in a single potential well. Nonetheless, as temperature is raised to room conditions, simulations evidenced a rapid “classical” shuttling of the proton due to the onset of a two-wells free energy profile separated by a free energy barrier of the order of <i>kT</i>. This picture, supported by the agreement between simulated and experimental IR spectra, shows that the titania surface acts like a protecting group for the carboxylic acid functionality. Such a conceptual insight might help rationalize the chemical processes of carboxylic species on TiO₂ surfaces.</p><div> <div> <div><a></a> <p> </p> </div> </div> </div>

Quantum vs Thermal Effects in Formic Acid Adsorption on (101) TiO2 Anatase Surfaces

<p>Carboxylic acids adsorption on anatase TiO₂ is a key process in circular economy and sustainability. Yet, in spite of several decades of investigations, its intimate working mechanisms still remain elusive. In particular, the behavior of the acid proton and its localization – either on the molecule or on the surface – are still open issues. By modeling the adsorption of formic acid on top of regular (101) anatase TiO₂ surfaces, we found that, in the 0 K limit, the acid proton is shared between a carboxylic oxygen and a surface oxygen. In this regime, the proton behavior is mainly governed by quantum delocalization effects in a single potential well. Nonetheless, as temperature is raised to room conditions, simulations evidenced a rapid “classical” shuttling of the proton due to the onset of a two-wells free energy profile separated by a free energy barrier of the order of <i>kT</i>. This picture, supported by the agreement between simulated and experimental IR spectra, shows that the titania surface acts like a protecting group for the carboxylic acid functionality. Such a conceptual insight might help rationalize the chemical processes of carboxylic species on TiO₂ surfaces.</p><div> <div> <div><a></a> <p> </p> </div> </div> </div>