The effect of keto defect on the photophysical properties and electronic structure of neutral and charged LOPP

The effect of keto defect on the photophysical properties and electronic structure of neutral and charged (dicationic and dianionic) LOPP (ladder-type oligoparaphenylenes) are investigated theoretically with quantum chemical methods. The theoretical results show that the influence of the keto defect to the neutral LOPP is substantially, which results in undesired green emission; while the influence of the keto defect to the charged LOPP is little, since: (1) from the results of 3D cube representations, the electron (hole) density becomes more similar to that of a free charge carrier in conduction (valence) band, and (2) from the results of 2D site representation, the exciton size of the charged species are much larger than that of the neutral ones. Conclusions are also obtained that undesired green emission results from the localized excited states in fluorescence.