Phthalocyanine Molecules with Extremely Strong Two-Photon Absorption for 3D Rewritable Optical Information Storage

摘要

Phthalocyanines (Pcs) show exceptional stability against high temperatures (up to 900℃, for certain metallophthalocyanines), harsh chemical environments (strong acids and bases), γ-radiation (up to 100 MRad) and neutron radiation (up to 10~(19) thermal neutrons/cm~2). On the other hand, PCS exhibit a number of unique physical properties, including semi-conductivity, photoconductivity, large linear and nonlinear optical coefficients, and the ability of photo-switch between two different forms, in case of non-symmetrical metal-free PCS. This has led to an advancement of phthalocyanine-based prototype field-effect transistors, gas- and photo-sensors, solar cells, optical power limiters, and optical memory devices (CDs). For increasing the capacity of carriers of information, it has been suggested to use the effect of simultaneous two-photon absorption (2PA), which can allow for writing and reading information in many layers, thus resulting in Terabyte (TB) disks. Our estimation of the signal-to-noise ratio shows, however, that for fast (MB/s) processing, molecular 2PA cross section must be extremely large, σ_2 > 10~3 -- 10~4 GM (1GM = 10~(-50) cm~4 s), which has not been achieved yet in any photochromic material. In this paper we demonstrate, for the first time, that some specially designed non-symmetric metal-free phthahlocyanines are almost ideally suited for TB rewritable memory due to their extremely high, resonantly enhanced, 2PA cross section (～ 10~4 GM) in near-IR region and their intrinsic ability of reversible photo-tautomerization at lowered (～ 100 K) temperatures. We discuss how the special technical specifications, such as short pulse laser excitation and lowered working temperature, can be satisfied for space and terrestrial application.