First-principles calculations of anharmonic and deuteration effects on photophysical properties of polyacenes and porphyrinoids
A new method for calculating internal conversion rate constants (kIC), including the anharmonic effects, and using the lagrangian multiplier technique, is proposed. The deuteration effect on kIC was investigated for naphthalene, antracene, free base porphine (H2P) and tetraphenylporpyirn (H2TPP). The results show that anharmonic effects are important when calculating kIC for transitions between electronic states that are energetically separated (E) by more than 20000-25000 cm-1. Also, anharmonic effects is important when E<20000-25000 cm-1 with the presence of the accepting X-H stretching modes with the frequency larger than 2000 cm-1. The calculations show that there is a mixture between the S1 and S2 states of napthtalene induced by a non-adiabatic interaction. The non-adiabatic interaction matrix element between the S1 and S2 states is equal to 180 cm-1 and 110 cm-1 for the normal and fully deuterated naphthalene stucture and this difference is important for the fluorescence quantum yield estimation. Besides aromatic hydrocarbons, (H2P) and (H2TPP), the kIC is calculated for pyrometene (PM567) and tetraoxacirculene (4B) with a detailed analysis of the effects of vibrational anharmonicity.