Isolated large π systems in pyrene-fluorene derivatives for intramolecular through-space interaction in organic semiconductors

In order to give an insight of the special spectra of isolated π systems, a series of pyrene-fluorene derivatives, with conjugated or non-conjugated pyrene groups, were systematically studied. Besides absorption of non-conjugated pyrene itself and main conjugation chain, all the pyrene-non-conjugated large conjugated materials show a characteristic sharp absorption peak at ∼352 nm. Through systematical investigation, this special absorption peak was attributed to the intramolecular through-space interaction between the two isolated large π systems. Such interaction could also be defined as π-π hyperconjugation. And from quantum calculation, this intramolecular interaction does shorten the length of single bond. Through systematical research, the condition of this intramolecular through-space interaction is proved to be that the non-conjugated pyrene must have projection on fluorene plane. And then this effect is applied to explain the improved injection ability of the materials by bringing out one simple hopping model.