Synthesis of polyethyleneimines protonated by 1-pyrenesulfonic acid and their usability for solublization of single-walled carbon nanotube

Reaction of 1-pyrenesulfonic acid (Pyr-SO3H) with branched polyethyleneimine (PEI) in molar ratios of 1:1, 1:2, 1:3, and 1:4 produced PEIs with sulfopyrenyl pendant groups, denoted as Pyr-PEI(1:1), Pyr-PEI(1:2), Pyr-PEI(1:3), and Pyr-PEI(1:4), respectively; the degrees of protonation depended on the feed ratios of Pyr-SO3H/PEI. Treatment of single-walled carbon nanotube (SWNT) with Pyr-PEIs caused adhering of the pyrenyl group on the SWNT surface and produced soluble composites, SWNT-Pyr-PEIs. UV-vis and photoluminescence (PL) measurements indicated that the absorbance and PL intensity corresponding to SWNT in SWNT-Pyr-PEIs increased with increasing the content of the PEI unit in the composites. The electrical conductivities of SWNT-Pyr-PEIs were higher than that of pristine SWNT owing to n-doping, based on electron migration from the PEI unit to the SWNT.