Nonlinear optical characteristics of non-covalently functionalised graphene-pyrene-conjugated phthalocyanine hybrids

Improving the non-linear absorption properties of graphene materials is valuable for optical limiting applications. We report the non-linear optical characteristics of new hybrid materials formed by the non-covalent functionalisation of graphene nanoplatelets (GNs) with pyrene-conjugated Zn(II) phthalocyanines and pyreneconjugated Zn(II) azaphthalocyanines. The GN-pyrene-conjugated Zn(II) phthalocyanine hybrid (GPc) shows a promising change from the two-photon absorption behaviour of GNs to three-photon absorption, the first such example in a graphene based hybrid system under nanosecond pulse excitation. Fluorescence and transient absorption spectroscopies are employed to describe the non-linear optical phenomena of the prepared hybrid materials. The GPc hybrid exhibits a low optical limiting threshold induced by three-photon absorption and a favourable linear transmittance (above 90%). The GN-pyrene-conjugated azaphthalocyanine hybrid (GAzaPc) also shows promising non-linear optical coefficients. A unique optical limiting performance (80% reduction in intensity) is achieved throughout the experimental range of excitation intensities. Our research offers a way to design hybrid material structures with a large effective three-photon absorption coefficient and nearly constant optical limitation across a wide intensity range with 92% linear transmittance, which would be highly useful in non-linear photonic applications.

Automated summary

Improving the non-linear absorption properties of graphene materials is crucial for optical limiting applications. The hybrid materials formed by non-covalent functionalisation of graphene nanoplatelets with pyrene-conjugated Zn(II) phthalocyanines and azaphthalocyanines show promising non-linear optical characteristics, such as three-photon absorption behavior and unique optical limiting performance. These hybrid structures offer a way to achieve large effective three-photon absorption coefficients and nearly constant optical limitation across a wide intensity range, which would be highly beneficial for non-linear photonic applications.