This Small Business Innovation Research Phase II project aims to develop a prototype instrument which combines pulsed-laser photoacoustic detection with optical measurements of fluorescence to determine fluorescence quantum yields. The instrument will be more accurate, easier to operate, and less expensive than existing methods for measuring quantum yields. In addition, this photoacoustic method will become a powerful tool for elucidating the photophysics of fluorescent and nonfluorescent chromophores. It will measure photo-induced molecular volume changes and provide important information of the disposition of electronic excited state energies into various pathways, including intersystem crossing, electron ejection, and other excited state reactions. This project will attempt to design and build a sophisticated prototype and test it by measuring quantum yields of several dyes with different spectral properties. The research will also examine photo-induced molecular volume changes in a series of common laser dyes with the intention of developing a molecular volume standard. A relatively complex fluorescent, photochemical molecule, pyranine, will be analyzed for all aspects of its photophysics and photochemistry. Finally, the photophysics of chromophores bound to proteins will be examined. If the project is successful, the instrument will become an important analytical tool providing quantitative information on molecular excited states for all those laboratories that make serious use of fluorescing chromophores as probes.
