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

Abstract

Fluorescence quantum yields ( Φ f) of polycyclic aromatic molecules (PAMs) having the S 1 state with character L a are largely determined by the presence or absence of the S 1→ T 2 intersystem crossing channel. On the basis of this knowledge, the correlation between the measured Φ f and the S 1– T 2 energy differences [ E( S 1)– E( T 2)] 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 Φ f ( Φ f≈1) from those having Φ f substantially smaller than unity ( Φ f≪1) by a threshold value of E( S 1)– E( T 2). The CIS calculation of E( S 1)– E( T 2) can be applied to the screening of Φ f≈1 PAMs.