Mechanisms of optical limiting in fullerene-doped π-conjugated organic structures demonstrated with polyimide and COANP molecules

Possible mechanisms of optical limiting of visible radiation in conjugated organic structures based on polyimides and substituted pyridines sensitized with C₆₀ and/or C₇₀ fullerenes are studied using the Z-scan method. It is shown that reverse saturable absorption, two-photon absorption, and complex formation between the donor fragment of a π-conjugated molecule and fullerene contribute to the processes of nonlinear absorption. The absorption cross sections for excited states of the charge transfer complexes based on polyimide 6B-C₇₀ and 2-cyclooctylamino-5-nitropyridine-C₇₀ systems are calculated. The data obtained are quantitatively interpreted and compared with those provided by alternative methods.