I have conducted studies of the optical properties of two model conjugated systems (poly-(p-phenylenevinylene) and a set of zinc-centred oligo-(porphyrins) ). Various optical probing techniques have been employed to study the nature and behaviour of the primary photoexcited state of poly-(p-phenylenevinylene) (PPV) and photogenerated charged states within the porphyrins. Implantation of PPV films by high energy (30ke V) ions has been employed to introduce controlled damage into the film. Subsequently, studies of the absorption, fluorescence, photo-induced absorption and photocurrent response of the treated films has been used to model the behaviour of the photogenerated exciton after excitation. At the same time, the . probing sheds light on the mechanisms at work in the deceleration of the implanted ions and the nature and location of the damage produced. A study of the effect of applied electrical field on the fluorescence of PPV is analysed in terms of existing models of exciton dissociation. The results support the view of the primary photo-excitation as a self-localised exciton with a binding energy of some tenths of an electron volt and a spatial extent of a few nanometers. Measurements of the effect of current flow in the device extend the study of exciton diffusion started in the study of ion implanted PPV. Measurements of persistent fluorescence quenching subsequent to current flow in the material suggest that charge accumulation may be a serious limiting factor in the performance of polymer light-emitting diodes. Studies of the absorption, fluorescence and photo-induced absorption of a set of novel conjugated oligomers based on a zinc-centred porphyrin, show that the optical properties are strongly influenced by charged states generated from the dissociation of the primary photoexcitation. Such charged states are found to have lifetimes of some milliseconds even at room temperature.