Controlling the Movability and Excimer Formation of Functional Organic Molecules

An excimer is an excited dimer complex made of two π-conjugated fluorophore molecules such that one is in the ground, and the other in the excited state. In the solid state, the intensity of the excimer emission, which is mainly caused by the formation of the excited dimer, heavily depends on the movability of the excited π-conjugated molecule. In this study, we report that organic salts composed of disulfonic acid with a common π-conjugated molecule, 2,2′-bithiophene (BT), can act as functional excimer moieties, while linear alkylamines may be used as arrangement-controlling moieties. Furthermore, we found that the intensity of the excimer emission can be drastically changed by fixing the BT moiety, which can be achieved via the interaction of the alkyl groups (i.e., the anchor effect). The experimental relationship between the movability of the π-conjugated molecule and the intensity of the excimer emission was revealed without changing the structure and arrangement of the functional organic molecules in the solid state. We prepared the organic salts composed of disulfonic acid with a common π-conjugated molecule, 2,2′-bithiophene (BT), and linear alkylamines, and revealed that the intermolecular interaction of the alkyl groups between adjacent alkylamines contributed the fixation effect of the BT moiety (i.e. the anchor effect), which drastically affected the excimer formation.