Optical nonlinearities and excited state dynamics of self-assembled cobalt phthalocyanine multilayer films

•Ultrathin multilayer films containing cobalt phthalocyanine and PDDA were fabricated.•Fully self-assembled with homogenous morphology and well-ordered structure.•The ultrathin films exhibited notable optical nonlinearities with picosecond pulses.•Pump probe result revealed that the films had fast excited state relaxation. An ultrathin composite films containing cobalt phthalocyanine (CoPc) and poly(diallydimethyl ammonium chloride) (PDDA) were fabricated through layer-by-layer assembly technique. The resulting films were characterized by UV-Vis spectroscopy and atomic force microscopy. Their third-order nonlinear optical properties and photo-excitation dynamics were investigated with 20 ps laser pulses at 532 nm. The results demonstrate that the ultrathin films have notable third order optical nonlinearities (χ(3)∼4.7 × 10−9 (esu)) and fast excited-state relaxation (τ∼67 ± 6 ps), indicating their potential applications in future nonlinear optical devices.