CAS: Exploiting Pro-Aromaticity for Triplet Photochemistry: Synthesis, Aromaticity, & Photophysics

With support from the Chemical Structure, Dynamic & Mechanism-B Program of the Chemistry Division, Jean-Luc Ayitou of the Department of Chemistry at the University of Illinois Chicago (UIC) is developing novel pro-aromatic heavy-atom-free organic chromophores viz. diketopyrrolopyrroles (DPP) and dipyrrolonaphthyridine-diones (DPND) which exhibit attractive light-harvesting and photophysical properties. The ultimate goal of this research is to exploit the intrinsic molecular properties such as aromaticity to modulate the photo-behavior and the spin state of the proposed DPP and DPND chromophores, which can be tailored for applications such as triplet photosensitization, photodynamic therapy and solar energy conversion into solar fuels. Moreover, the proposed DPP and DPND chromophores can be further derivatized to engineer next-generation photo-materials for several other applications. Dr. Ayitou will mentor and train students to use the tools of synthetic organic chemistry, computational modeling, and advanced spectroscopy to accomplish the proposed goals to give them exposure to multi-disciplinary science. Additional educational components of the proposed research include outreach activities promoting STEM (science, technology, engineering and mathematics) education across Illinois. Molecular aromaticity is a fundamental characteristic often used to describe pi-conjugated annulenes. Classical aromatic compounds can be easily prepared and handled at ambient conditions for various applications. However, these compounds become unstable upon photoexcitation due to reduced local/global resonance energy stabilization in their excited state. Alternatively, pi-conjugated systems that display (pro)aromaticity and/or adaptivity exhibit greater stabilization in their photo-excited state leading to efficient ISC to populate the triplet manifold. Hence, truncating local and global aromaticity in pi-conjugated organic chromophores would create novel triplet chromophores with attractive photophysical properties. Expectedly, exploiting molecular aromaticity to modulate triplet photochemistry can open new avenues in spin chemistry and triplet photochemistry/photosensitization. Also,Dr. Ayitou and his team are investigating the synergistic role of molecular aromaticity and spin-orbit coupling in impacting triplet photo-dynamics and kinetics in the proposed DPP and DPND systems. At the fundamental level, using advanced photophysical and computational tools, the Ayitou team aims to determine whether the proposed chromophoric systems exhibit truncated and/or adaptive aromaticity in their photo-excited state. Furthermore, the team will assess how structural factors, molecular topology, and the electronic nature of various substituents in the proposed DPP and DPND influence their corresponding triplet photochemistry. Ultimately, this project aims to create a library of purely organic triplet chromophores and novel photo-materials that can be further explored in solar energy conversion and biomedical applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.