Tuning of the height of energy barrier between locally-excited and charge transfer states by altering the fusing position of o -carborane in phenylnaphthalene.

We synthesized two types of the regioisomers fused by a phenylnaphthalene ring with variable connection points to the o -carborane scaffold. In this paper, we describe their photoluminescence (PL) properties and detailed photochemical mechanisms. According to the series of optical measurements, interestingly, they showed different PL characters in terms of wavelength and the dual-emission character despite that they have the common aromatic unit. Variable-temperature PL measurements and quantum chemical calculations suggested that the substitution position of aryl groups to o -carborane plays an important role in determining the energy barrier to the intramolecular charge-transfer (ICT) state at the S 1 state. Finally, it is revealed that the relative position of the C-C bond of o -carborane and the aryl center should be responsible for the photophysical events of aryl- o -carboranes.