Megamerger of porphyrin (phthalocyanine) with azulene-based graphene nanosheets for high-performance nonlinear optical materials†

Abstract

Due to their good physical and chemical properties, porphyrins and phthalocyanines are promising nonlinear optical (NLO) materials, particularly for biological applications. However, the design of excellent porphyrin or phthalocyanine NLO materials with both strong second and third NLO properties remains challenging. In the present work, the merger of azulene-based graphene (azugraphene) nanosheets with porphyrin (phthalocyanine) brings about hybrid structures with strong NLO responses and good chemical stability through polarizing the enhanced π-conjugation. Among these designed molecules, the azugraphene merged porphyrin P_N-3A-A has the largest static first hyperpolarizability per heavy atom (〈β₀〉/N of 449.99 × 10⁻³⁰ esu) and second hyperpolarizability per heavy atom (〈γ₀〉/N of −11.28 × 10⁻³⁴ esu). The addition of Mg into P_N-3A-A further enhances the second and third order NLO properties, and the 〈β₀〉/N and 〈γ₀〉/N values of Mg-P_N-3A-A reach 454.07 × 10⁻³⁰ esu and −11.37 × 10⁻³⁴ esu, respectively. The strong third order NLO responses of the porphyrin and metalloporphyrin derivatives in the near-infrared region confer these molecules potential applications in optoelectronics and biomedical engineering owing to the extended π-conjugation of the N-doped polar graphene nanosheets and the biocompatibility of porphyrin. This work provides useful information for designing multi-functional materials by properly combining the merits of functional components.