Investigations of Two-Photon Absorption and Dissociation of Nitrodibenzofuran Based Photocages

Abstract

The ability to selectively deliver bioactive molecules with high spatial and temporal resolution has applications in many areas of chemical biology and drug delivery. Using photocages, drugs can be selectively released within specific areas of tissue. When chemically bound, these groups deactivate the drug’s biological activity. Light of a sufficient energy can then be used to break the bond linking the drug to the cage. Photocages typically require the energy of one UV photon to dissociate, but UV photons have low penetration depth and can damage tissue. Two-photon absorption (2PA) can be used to break the bond using the energy of two NIR photons. There is, however, a lack of understanding of the design principles for producing photocages that have both high 2PA cross sections and high uncaging efficiencies. The purpose of this research was to study the structure of a photocage affects the dynamics of two-photon absorption and two-photon induced dissociation in a series of dibenzofuran based photocages.The first two sections of this dissertation investigate the effect that structural modification of the photocage and choice of leaving group have on the photophysical properties of the NDBF system. Extending the conjugation or adding electron-donating groups to NDBF can increase the 2PA cross section and dissociation rate. The leaving group choice strongly influences the dissociation rate, but affects the 2PA cross section much less. The third section investigates the dynamics of dissociation and to what extent they influence the overall dissociation rate. It was found that the amount of photocages that initially dissociate does not correlate with overall dissociation rate. Lastly, computational methods were used to investigate potential molecular structures that can be used as more efficient photocages. It was determined that NDBF dimers exhibit greatly enhanced 2PA cross sections and should be pursued synthetically.