With the ever pressing demand for higher storage densities and faster data-processing rates, future information memory systems will be required to operate mostly in the photon mode, where data can be written, read, and erased in binary states using different photons. [1,2] In photon-mode recording, light characteristics such as wavelength, polarization, and phase can be multiplexed to enable data storage and thus have the potential to increase dramatically the achievable memory density.[3±5] One promising approach is the development of photochromic materials. These materials, due to their ability to change between two distinct isomeric states, where each state can represent ª0º or ª1º of a digital mode, via irradiation at different wavelengths, are promising candidate optical storage materials as opposed to the heat-mode recording employed with the optical media currently in use. The use of photochromic materials in three-dimensional (3D) memory systems is desirable because they present several major advantages compared to current optical systems, including their erasable/rewritable capability, high resolution, and high sensitivity. Utilizing two-photon excitation is the key to achieving effective 3D memory systems. Several photochromic materials having properties making them suitable as 3D memory recording media have been described. [4] Spirooxazines (SO) are well-known photochromic compounds that have been attracting much interest from the viewpoints of both fundamental elucidation of photochemical reactions and their potential applications to optical memories.[6±12] The photochromism of these molecules is due to the photocleavage of the spiro-bond under UV irradiation, creating a deeply colored ring-opened merocyanine form, which has a broad absorption band in the visible region and can be converted back to the closed-ring form by visible-light irradiation or heating. The colored form of spironaphthoxazine is composed of four isomers and the most stable structure has been found to be the quinoidal form (TTC structure shown in Scheme 1). [13] In past decades, spirooxazines' application in memories has been severely restricted by the short lifetime of the colored photomerocyanine species, which reverts thermally to the closed-ring colorless spirooxazine form with a half-reaction time of 1±10 3 s and an apparent activation energy of 14±30 kcal mol ±1 . [12] Many theoretical studies of the ring-closing reaction dynamics have been performed and various methods of stabilizing the merocyanine form have been developed.[14±18]However, to the best of our knowledge, there is no report on the realization of practical optical information storage using spirooxazine derivatives, in part due to the difficulty in making the open-ring photomerocyanine form of the spirooxazine molecule stable enough to ensure that the recorded data can be maintained for a comparatively long time. Here, we report a novel spironaphthoxazine molecule that has a reasonably stable merocyanine form and demonstrate that it is a suitable material for b...

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