Planar Porphyrin Molecules for Photovoltaic Devices

The high chemical stability and wide sun spectrum absorbance distinguishes planar porphyrin (Py) molecules from other high mobility organic semiconductors and stimulates research on improving photophysical and semiconducting properties of this compound. The carrier transport in organic molecular solids is governed by the extent of intermolecular orbital coupling (transfer integrals), where larger orbital coupling can afford better transport properties. One of the approaches to enhance orbital coupling is to use π-extended molecules. Another approach is to use the self-organizing nature of organic molecules in which alkyl groups act as the driving force for molecular ordering in the solid state. Preliminary results from our group show that alkyl groups render different molecular alignment of the semiconducting core to orient differently, thereby changing the physical properties of their solid thin films. We propose to synthesize a series of Py molecules with different alkyl side chains and study the physical properties at their solid thin film state. From our preliminary results, in solution modified and unmodified planar Py molecules exhibited the same photo-physical properties; however, in solid thin films they self-assemble and stack differently due to the alkylation eventually changing their physical properties. With these design strategies for molecular orientation, we propose a systematic analysis on the physical properties of the alkylation of Py molecules.