Photochromic manipulation of energy and electron transfer

Photochromic molecules, which by definition have two or more isomers with different absorption properties, are ideally suited for the manipulation of energy transfer and electron transfer when covalently attached to other chromophores. This dissertation describes the synthesis, characterization, and function of a number of organic molecular systems incorporating photochromic functional groups, in which energy transfer and electron transfer are manipulated. Steady-state absorbance and fluorescence, as well as time-resolved fluorescence and transient absorbance spectroscopies were used to quantify the manner in which electron transfer and energy transfer can be switched. Directional electron transfer is demonstrated, in which electron transfer can be toggled between two distinct paths with near perfect specificity. Incorporation of photochromic units into larger multichromophore arrays allows for the demonstration of various molecular logic functions. Also described is a self-regulating molecular system that down-regulates photoinduced electron transfer under high white light flux such that it is functionally analogous to photoprotective mechanisms employed in photosynthetic plants. These studies overall demonstrate more complex switching of the photophysical properties of organic molecules than has been shown previously and may point the way to more advanced organic electronics applications.