Spectroscopic investigation on porphyrins nano-assemblies onto gold nanorods

The interaction between gold nanorods (Au NRs), synthesized by a conventional seeded growth protocol, and theanionic tetrakis-(4-sulfonatophenyl)porphyrin (TPPS4) has been investigated through various spectroscopictechniques. At neutral pH, the formation of H-aggregates and the inclusion of porphyrin monomers in CTAB micellescovering the nanorods have been evidenced. Under mild acidic conditions (pH=3) a nano-hybrid assemblyof porphyrin J-aggregates and Au NRs has been revealed. For the sake of comparison, Cu(II) and Zn(II) metalporphyrin derivatives as well as a cationic porphyrin have been studied in the same experimental conditions,showing that: i) CuTPPS4 forms porphyrin H-dimers onto the Au NRs; ii) ZnTPPS4 undergoes to demetallation,followed by acidification of the central core and eventually aggregation onto Au NRs; iii) cationic porphyrindoes not interact with Au NRs.