Moreover, the photoluminescence decays can now only be fitted with a biexponential decay, yielding τ1 = 1.49 ns and a delayed component of τ2 = 9.23 ns for PyFlCz and τ1 = 3.07 ns and τ2 = 16.6 ns for PyPhCz (see Table and Figure ). Altogether, the τ1 are slightly longer in the solid state than in solution (cf. Table and). Together with the increased ϕ this extension in τ1 photoluminescence lifetime points at a reduction of non-radiative decay pathways in the solid CBP matrix. Frozen in the matrix, PyFlCz and PyPhCz lack certain modes of freedom, like the rotation of the donor around the bond with the pyrene acceptor, which may present a loss channel in solution. Moreover, it is interesting that PyFlCz with the higher ϕ exhibits a smaller τ1. When we calculate the fluorescence decay rate kf and the rate for non-radiative decay knr for both molecules, we observe that the knr are relatively similar (see Table and Equation S3