π–π binding ability of different carbon nano-materials with aromatic phthalocyanine molecules: Comparison between graphene, graphene oxide and carbon nanotubes

• The π–π binding of different carbon nanomaterials with phthalocyanine (Pc) was studied.
• Strong π–π binding occurred for graphene and graphene oxide but not for SWCNT.
• The binding ability with ground state Pc is G ≫ GO ≫ SWCNT.
• However, the binding ability with excited state Pc is G ≫ SWCNT ≫ GO.
• An effective quenching sphere model is needed for the fluorescence data analysis.

The π–π stacking ability of graphene sheets (GS), graphene oxide (GO), and single walled carbon nanotubes (SWCNT) with phthalocyanine (Pc) molecules was studied by the UV–vis absorption, steady state and time-resolved fluorescence spectra. Absorption spectra revealed that strong π–π binding with the Pc ground state (S0) occurred for GS and GO but not for SWCNT, the binding ability is GS ≫ GO ≫ SWCNT. However, when a Pc molecule is photoexcited, fluorescence study shows that the π–π interaction capability is changed to GS ≫ SWCNT ≫ GO. Although SWCNT exhibits low ability to bind Pc S0 state, it strongly interacts with Pc S1 state. The data analysis shows that the dynamic quenching for the nanoscaled carbon quenchers still obeys linear Stern–Volmer relationship, but the static quenching is not linear. An exponential expression is needed to fit the data for GS and SWCNT, which indicates that an effective quenching sphere model is valid for the nanoscaled fluorescence quenchers.