Nonlinear-Optical Properties of Self-Assembled Molecular J-Aggregates of Pseudoisocyanine in Nanometer Films

Abstract

J-aggregates, first discovered by Jelley and Scheibe in 1936 [1, 2] for cyanine dyes, have been studied for many years [3]. They are well-known for their unique optical properties, such as a strong absorption, narrow line widths, and high optical non-linearities. Their role as photographic sensitizers can hardly be overestimated [4–6]. Recent studies have shown that a number of biological light-harvesting systems, such as the LH1 and LH2 complexes of purple photosynthetic bacteria [7] and the chlorosome of green photosynthetic bacteria [8], consist of aggregated bacterio-chlorophylls. Thus, aggregates of dye molecules may be used to mimic light harvesting arrays and to prepare artificial photosynthetic systems. Another new development is the efficient electroluminescence revealed in single-layer light-emitting diodes based on electron-hole conducting polymers containing nano-crystalline phases of J-aggregates of cyanine dyes [9]. Finally, the property of J-aggregates that still holds most promise for the near fixture, is their high nonlinear (cubic) optical susceptibility, χ(3) ∼ 10-6 – 10-5 esu, with a fast response time (less than 1 ps) at the J-peak resonance [10–12]. As shown in [13], films of J-aggregates with bistable behavior may be the basis for two-dimensional optical switches, controllable by light. The nonlinear-optical properties of organic dye J-aggregates have been intensively studied for application in future optical telecommunication and signal processing systems with ultrahigh bit rates (Tbit/s) [14].