Effect of structural modifications in the spectral and laser properties of perylenediimide derivatives

The aim of this work was to design strategies to improve the performance of solid-state lasers and amplifiers based on perylenediimide (PDI) derivatives as active materials. So, the effect of different types of modifications of the chemical structure of PDIs in their spectral, electrochemical, and laser properties in both solution and PDI--doped polystyrene films at various concentrations has been investigated. In particular, we focused on controlling the wavelength of emission in order to tune the laser wavelength as well as in increasing the amount of PDI in the films in order to decrease the laser thresholds, while keeping a good photostability. Three types of modifications of the chemical structure were investigated: (a) symmetrical substitution at the imide nitrogen positions (PDI 1); (b) substitution at the bay positions in the PDI core (PDI 4); and (c) modification in the dicarboximide group (PDI 5). All three derivatives were soluble and showed good n-type acceptor ability. Routes b and c led to red shifts in the absorption and photoluminescence (PL) emission, although the PL quantum yield decreased considerably. Amplified spontaneous emission (ASE) was observed in films doped with PDI 1 (lambda = 579 nm) and PDI 4 (lambda = 599 nm). The best performance, with an ASE threshold of 15 kW/cm(2) and a photostability halflife of 31 x 10(3) pump pulses, was obtained for films doped with 0.75 wt % of PDI 1 (route 1). PDI I-based materials are among the most photostable reported in the literature and show very-reasonable thresholds. Moreover, these materials are particularly interesting in the field of data communications based on polymer optical fibers because they emit at wavelengths close to 570 nm, which constitutes the second low-loss transmission window in poly(methyl methacrylate).