Covalent decoration onto the outer walls of double walled carbon nanotubes with perylenediimides†
The outer walls of double walled carbon nanotubes (DWCNTs) have been selectively functionalized with different substituted perylenediimides (PDIs) leaving the inner walls intact. The spacer connecting DWCNTs and PDIs, and the PDI macrocycle position has been varied to visualize the DWCNT–PDI interactions in the hybrids. Evidence of outer wall functionalization and the degree of PDI substitution on DWCNTs were arrived from HR-TEM, AFM, FTIR, TGA, XPS and Raman techniques while nanotube–photosentisizer interactions were probed from studies involving optical absorbance and emission, and electrochemical techniques. Fine-tuning of the electronic states of PDIs in the hybrids was possible with the present covalent approach. The fluorescence of PDIs in the hybrids was found to be quenched (60–70%) due to interactions with DWCNTs. Further, femtosecond transient absorption and photocatalytic electron pooling studies were performed to seek evidence of charge separation in these hybrids. In agreement with earlier studies, evidence of charge separation from the transient studies was bleak, and accordingly, yields of photocatalytic electron pooling were much lower than those reported earlier for fullerene and single walled carbon nanotube based hybrids. The present study is suggestive of further tuning of donor–acceptor energy levels in DWCNT derived hybrids for efficient charge separation and stabilization.