Carbon nanotube-acridine nanohybrids: spectroscopic characterization of photoinduced electron transfer.

Single-walled carbon nanotubes (NT) were covalently functionalized with either 9-phenyl acridine (PhA) or 10-methyl-9-phenyl acridinium (PhMeA(+)). Absorption and fluorescence properties of acridine derivatives tethered to the nanotubes were studied in homogeneous dispersions. Exciplex emission was observed for NT functionalized with 9-phenylacridine. This phenomenon was attributed to an "intramolecular" interaction between excited phenyl acridine and carbon nanotubes. Interestingly, reverse photoinduced electron transfer from the nanotube to 10-methyl-9-phenylacridinium was detected for the NT-PhMeA(+) nanohybrid. This electron transfer led to a strong quenching of the acridinium fluorescence and to the formation of a metastable acridine radical. Evidence for the formation of this radical was obtained by ESR studies.