Discovering the secrets of photosynthesis in order to store solar Energy in a more efficient manner and use it where and when necessary. This is the challenge faced in the "EnLight" project undertaken by the Department of Chemistry and Industrial Chemistry at the University of Pisa which has been granted funding of one million three hundred thousand euros by the European Community over the five-year period 2011-2015. Professor Benedetta Mennucci is leading the research project at the MoLECoLab laboratory in the University of Pisa and coordinating a team made up of three doctorate students and three researchers.
The idea of understanding the mechanisms of photosynthesis in order to design efficient artificial photosynthetic systems also stems from the need to overcome the limits of the existing photovoltaic cells. In fact, the present systems only collect a small percentage of the energy which is transformed into electricity and they do not work continuously but only when there is daylight, so in order to use the energy at night electric accumulators are needed. However, these large batteries are impossible to produce on a large scale.
"What interests us most," explains Benedetta Mennucci, "is the first phase of the photosynthesis, generally known as light-harvesting, above all because it has a practically perfect efficiency, in other words, only a tiny part of the light absorbed is lost."
During this phase, protein complexes known as "antenna complexes" capture sunlight through pigments found on the inside and then transfer it to other protein complexes called "reaction centres", where the energy is used to start chemical processes. The "EnLight" project studies the development of models and computational calculation codes used to analyse the light-harvesting in order to clarify the molecular mechanisms behind this efficiency as well as the role played by the various participants, or rather the pigment molecules, the protein matrix and the external environment.
"The difficulty with this simulation is that the mechanisms behind the processes of light- harvesting cannot be explained by the laws of traditional physics," concludes Professor Mennucci, "given that the interaction between light and matter and its transformation into chemical energy occurs through atoms and molecules which are microscopic systems that obey the laws of quantum mechanics. In particular, it could be quantum type mechanisms that favour the transmission of absorbed energy, allowing the pigments to 'work' collectively so that the same energy is not dispersed at each phase."