Ultrafast Nonlinear Optical Characteristics of Pyrene-Conjugated Azaphthalocyanines with Optical Limiting Behavior

We synthesized an efficient dual-directional multivalent pyrene-bearing azaphthalocyanine conjugate (AzaPc-pyrene) and alkyne-terminated azaphthalocyanine (AzaPc1). The ultrafast nonlinear optical characteristics of these macrocycles were studied using a near-infrared femtosecond (fs) Z-scan experiment. The results for these Pc solutions showed good nonlinear optical coefficients, low optical limiting threshold (38 mJ/cm2), and a good set of figures of merit that satisfied the criteria for optical switching materials, thus proving their usefulness in photonic applications. Comparison with other phthalocyanines showed that both AzaPc-pyrene and AzaPc1 are strong nonlinear optical materials. The most important outcome of our study was a huge enhancement in the nonlinear absorption value of AzaPc-pyrene in the film phase that was up to 105 times greater than the corresponding values for AzaPc1 solutions; this enhancement was established using ultrafast laser irradiation-induced deformations in AzaPc-pyrene-embedded PMMA films, whereas the AzaPc1 film showed saturable absorption behavior. A promising limiting threshold of 1.5 mJ/cm2 with very low linear absorption was achieved in the deformed pyrene-incorporated AzaPc films; this is lower than the previously reported values for highly nonlinear materials, making these materials as potential nonlinear optical materials in the near-infrared wavelength range.