Two-Photon Chemistry of Small Organic Chromophores

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Normally, a molecule can be induced to go from its normal ground state to an excited state by absorbing light (or a photon) with energy that matches the difference in energy between those two states. However, as predicted by Nobel laureate Maria Goeppert Mayer in the 1930's, the change from ground state to excited state can sometimes (depending on the properties of the molecule) be induced using two photons with each photon having about half the needed energy in a process called two-photon absorption. There is intense interest in this phenomena, since two-photon absorption (2PA) has several advantages over the more conventional one-photon absorption (1PA): the lower energy needed for 2PA is more compatible with photochemistry in biological systems due to the higher penetration abilities, and requirement for two-photons provides a much greater ability to irradiate microscopic areas, thus increasing the accuracy of irradiation. These advantages have led to a wide range of applications of two-photon chemistry in diverse areas ranging from health related fields (photodynamic therapy) to high tech fields (3D data storage).