One of the most important aspects of photosynthesis is the ability to form a long-lived ion pair state. This long-lived ion pair, if implemented in molecular devices or solar cells, could greatly increase efficiency by providing more opportunities to harness the energy that is produced. The goal of my current research project is to synthesize molecules that undergo photoinduced electron transfer to form long-lived ion pair states. In particular, I am making systems that form self-assembled aggregates in solution, which have potential to form long-lived ion pairs because the pi-pi interaction allows for charges to migrate through the stacked molecules. One of the chromophores I am working with is perylene-3,4;9,10-bis(dicarboximide) (PDI), which has been used in many self-assembling systems (Figure 1).
Figure 1. Electron transfer within pi-stacked molecules. PDI, one of the chromophores I will be using in my self-assembled systems.
I have also worked on a project in which I synthesized and characterized linear DA complexes. The series of molecules, in which julolidine was used as the donor, were modeled after the MeOAn-ANI-Me 2Ph-NI series of molecules previously studied by my group. The molecules were designed to probe the relationship between minor structural changes within a particular system and the photophysical properties it exhibits. One particularly interesting aspect of these systems is the formation of a charge transfer (CT) state, which promotes electron transfer to form the ion pair state by overcoming the initial energy required to separate the charges (Figure 2).
Figure 2. Molecules synthesized and a ground state absorption spectrum showing the CT state absorption at 450 nm.
Rates of charge separation in these systems were probed using femtosecond transient absorption (TA) spectroscopy. I used nanosecond TA spectroscopy to determine the rates of charge recombination within these systems and to monitor the yield of triplet as a function of changing magnetic field (Figure 3).
Figure 3. Nanosecond transient absorption spectra and kinetic trace at 480 nm for J-NMI-Me 2Ph-NI.
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