Photophysics and Photochemistry of Proton and Charge Transfer Type Organic Fluorophores

With the support of the Chemical Mechanism, Function, and Properties Program of the Division of Chemistry, Professor Lei Zhu of the Department of Chemistry and Biochemistry at Florida State University is developing photosensitive organic compounds with interesting emission or photochemical properties. The goal of this research is to understand the factors, be they structural or environmental, that control the behaviors of these compounds in response to light. In addition to enriching the knowledge base of relevant scientific areas such as photophysics and photochemistry, the discoveries on the fundamental front will likely lead to (1) the development of organic emitters whose emission colors can be tuned by the applied excitation energy in optical devices (e.g., organic LEDs), and (2) new methods of preparing highly functionalized indoles or pyrroles, which are sought after core structures of pharmaceutical drug candidates. This project will provide training opportunities to young scientists who aspire to be well-rounded teachers and innovators in the disciplines of organic and physical chemistry. The special emphasis on sharpening the critical thinking skills of the trainees will help them become problem solvers who will have to address real world challenges with complexity levels that are not defined by disciplines. In this project, Professor Lei Zhu and collaborating students will uncover the principles that govern the photophysical and photochemical properties of two categories of organic dyes, both of which have access in their electronically excited states to either proton transfer or charge transfer process, or both. The subjects of this project will be prepared, while their properties will be characterized by advanced spectroscopic and theoretical methods. The first category of the targeted fluorescent dyes will be capable of excited state proton transfer to produce excitation energy-dependent dual emission. This is not only a challenging property to produce from small molecular emitters but a potentially useful one, as the composite color or the ratio of two emission bands could then be altered by excitation energy in applications requiring color-shifting emitters. The second category of emissive compounds will contain a triazole core, and many of them are projected to possess high brightness in both solution and solid phases. Depending on the substitution pattern, these compounds will be either photoreactive to be converted to highly functionalized indoles or pyrroles, or photostable. The discoveries on the fundamental front of this project will endow predictive power for assisting the accurate design of dye structures that respond to photoirradiation with either proton transfer or charge transfer process. These processes will in turn trigger the emergence of new properties and functions that are targeted in this project – excitation-dependent dual emission, or photostable and photoreactive emissive compounds that can be easily prepared. The new properties encoded in the planned structures are projected to benefit technological sectors that call for versatile emitters with either durability or photo-convertibility. 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.