Both the photophysics and the fluorescence quenching behavior of an anionic conjugated polymer towards various small molecule quenchers can be modulated effectively by complexing the polymer with a simple countercharged detergent. For example upon adding odecyltrimethylammonium bromide (DTA) to the polymer, cationic quenchers such as methyl viologen become less effective while the quenching by neutral reagents - most notably nitroaromatics or cyanoaromatics - is enhanced. Thus, the polymer-detergent complex provides a new platform for sensing chemical agents via fluorescence quenching. Thin films formed from the complex exhibit high sensitivity to quenching by nitroaromatic vapor and reasonable reversibility.