Ab initio configuration interaction singles (CIS) study on polycyclic aromatic molecules (II): Predicting fluorescence quantum yields by calculating the excitation energies

Fluorescence quantum yields (Φf) of polycyclic aromatic molecules (PAMs) having the S1 state with character La are largely determined by the presence or absence of the S1→T2 intersystem crossing channel. On the basis of this knowledge, the correlation between the measured Φf and the S1-T2 energy differences [E(S1)-E(T2)] calculated by the configuration interaction singles (CIS) method have been investigated for the three polycyclic aromatic hydrocarbons (PAHs) and 12 anthracene derivatives. The results clearly show a separation of molecules having nearly unit Φf (Φf≈1) from those having Φf substantially smaller than unity (Φf≪1) by a threshold value of E(S1)-E(T2). The CIS calculation of E(S1)-E(T2) can be applied to the screening of Φf≈1 PAMs.