Abstract: Several fluorescent benzo[a]phenoxazinium chlorides possessing undecylamino chains with non-functionalised (methyl group) or functionalised terminals (hydroxyl, carboxylic acid and the ester group) as substituents at the 5-position of the heterocycles were used in photophysical studies with DNA. It was found that the functionalised terminal has a dramatic influence on the type of interaction with the hydroxyl group promoting intercalation, while the ester group promotes groove binding.