Kasha's empirical rule states that "the emitting electronic level of a given multiplicity is the lowest excited level of that multiplicity." This lack of emission from higher-lying states is simple to rationalize: internal conversion between excited states is much faster than photon emission. In other words, most chromophores with a singlet ground state end up in the minimum of the first excited state, S1, before they fluoresce. Nevertheless, fluorescence from higher-lying states, known as non-Kasha (or anti- Kasha) behavior, is well documented for several systems and is the basis of diverse applications exploring features such as tunable emission colors and improved luminescent quantum efficiency. Pyrene (see Figure ) is a prototypical chromophore with non-Kasha emission from a higher state. Consider, for instance, the results for low-pressure pyrene vapor reported by Baba et al. After a lowenergy excitation into the S2 state (3.86 eV; see Figure ), pyrene fluorescence has a single band at 3.26 eV (380 nm), assigned to S1 emission. However, if a higher excited state is promoted with absorption at 5.32 eV, a shoulder at 3.65 eV (340 nm) appears in the emission spectrum. This new feature is commonly assigned to a non-Kasha S2 emission. Similar features and assignments were also reported for pyrene in a supersonic jet and low-pressure vapor. Figure . Top: absorption spectrum of pyrene in the gas phase (150ºC) from Ref. 13. Bottom: fluorescence of pyrene in the low-pressure vapor after excitation at 3.86 eV (left), 4.66 eV (middle), and 5.32 eV (right) from Ref. 9.