About 85% of the world’s energy is derived from non-renewable sources—coal, petroleum, and natural gas. Solar photocatalysis is one way to potentially generate renewable fuels. Zinc dipyrrin complexes have the potential to be efficient sensitizers for reductive photochemistry, but their ability to form long-lived triplet excited states needs further investigation. The overall aim of this research is to compare the photophysical properties zinc and boron dipyrrin complexes and investigate the role of the charge separated state in triplet state formation. This presentation will describe the synthesis and purification of zinc and boron dipyrrin complexes and their photophysical characterization, including fluorescence quantum yields in a series of solvents and their emission at low temperatures.

About 85% of the world’s energy is derived from non-renewable sources—coal, petroleum, and natural gas. Solar photocatalysis is one way to potentially generate cheap renewable fuels by harnessing energy from the sun using a photosensitizer and converting it into chemical energy. The efficiency of a photosensitizer depends on its capacity to form a prolonged triplet excited state. Zinc dipyrrin complexes have the potential to be efficient sensitizers for reductive photochemistry, but their ability to form long-lived triplet excited states still needs extensive research. The overall aim of this research is to probe the role charge separation plays in the formation of triplet state in metal complexes of dipyrrin photosensitizers. The specific objectives are to synthesize and characterize zinc and boron dipyrrin complexes, analyze their photophysical properties—such as steady state spectroscopy, low temperature emission spectroscopy—and quantify their triplet states using time-resolved transient absorption spectroscopy.

About 85% of the world’s energy is derived from non-renewable sources—coal, petroleum, and natural gas. Solar photocatalysis is one way to potentially generate cheap renewable fuels by harnessing energy from the sun and converting it into chemical energy. Photosensitizers serve as materials that absorb and store sunlight in the form of chemical energy. The efficiency of a photosensitizer depends on its capacity to form a prolonged triplet excited state. Zinc dipyrrin complexes have the potential to be efficient sensitizers for reductive photochemistry, but their ability to form long-lived triplet excited states still needs extensive research. The overall aim of this research is to probe the role charge separation plays in the formation of triplet state in metal complexes of dipyrrin photosensitizers. The specific objectives are to synthesize and characterize zinc and boron dipyrrin complexes, analyze their photophysical properties—such as steady-state spectroscopy, low-temperature emission spectroscopy—and quantify their triplet states using time-resolved transient absorption spectroscopy.

The field of photochemistry is as innovative in development as it is broad in application. However, utilization of energy from the sun’s electromagnetic radiation remains secondary to the combustion of fossil fuels for the global energy consumption. This is neither a sustainable nor renewable system, and it has contributed to a major decline in the health of our global environment as the greenhouse gases emission has led to an incline in global temperatures and ocean acidity. To develop effective ways to utilize solar energy, experimental effort is being directed towards the understanding of photosensitizers, molecules which absorb solar radiation and initiate redox chemistry in CO2 reduction catalysts. Some zinc dipyrrins, one such class of photosensitizers, are theorized to undergo intersystem crossing through a charge separated state, a transition that is stabilized in polar solvents. This transition increases the lifetime of the excited state, as relaxation from the triplet state occurs much slower than from the singlet state. A phenyl substituted zinc dipyrrin was attempted to be synthesized and characterized using NMR spectroscopy to probe aromatic substituent effects on the molecule’s photophysics. The product was analyzed by UV-vis spectroscopy in order to confirm its purity and TLC analysis shows that the reaction kinetics are much slower in this phenyl substituted zinc dipyrrin than in previous reports, most likely due to the steric hindrance induced by the bulky phenyl substitutions.