Energy Barrier and Gaps between Two Excited States in a Dual-Emissive Carborane.

A thorough understanding of the internal conversion process between excited states is important for designing ideal multiple emissive materials. However, it is hard to experimentally measure both the energy barrier and energy gaps between the excited states of a compound. For a long time, it is dubious if what was measured is the energy gap or energy barrier between two excited states. In this paper, we designed 1-(pyren-2'-yl)-9,12-di(p-tolyl)-o-carborane (2), which shows dual emission in solution. Temperature-dependent fluorescence measurements show that the two emission bands in hexane are corresponding to two different excited states. The ratio of the emission bands is controlled by thermodynamics at higher temperatures and by kinetics at lower temperatures. Thus, the energy barrier and energy gaps between the two excited states of 2 can be experimentally estimated.