A CO2-responsive dispersant, N,N-dimethyl-N'-(pyren-I-ylmethyl) acetimidamidinium (PyAH(+)), which bears both a pyrene moiety and an amidinium cation, has been successfully synthesized. Through strong pi-pi interaction between the pyrene moiety;and single-walled carbon nanotubes (SWNTs), we have demonstrated that PyH+ can be modified onto SWNT surfaces to promote the dispersion of SWNTs in water. Furthermore, taking advantage of gas triggered interconversions between the amidinium cation and amidine, reversible control on the solubility of SWNTs has been achieved simply through alternated bubbling of CO2 and Ar. This work has demonstrated a new method for controlled dispersion and aggregation of SWNTs, and it may contribute to the development of gas responsive carbon materials.