Abstract: Ultrasonic irradiation was demonstrated to be an efficient technique for activating various organic transformations with short reaction times, fast reaction rate, high yields and sometimes good selectivity. Four new benzo[a]phenoxazinium chlorides possessing isopentylamino, (2-cyclohexylethyl)amino and phenethylamino groups at 5-position of the heterocyclic system were efficiently synthesised under ultrasound irradiation. Conventional heating procedure revealed that the present ultrasonic method provided several advantages in terms of reaction times and product yields. Photophysical studies in ethanol and water, as well as acid-base equilibrium studies of the probes were carried out.