Intra- and Intermolecular Charge Transfer in a Novel Dimer: Cooperatively Enhancing Second-Order Optical Nonlinearity

Abstract

Based on s-indaceno[1,2,3-cd;5,6,7-c′d′]diphenalene (1) consisting of two phenalenyl moieties, the monomer 2 and its dimer 22 are designed by boron and nitrogen atoms substituting the central carbon atoms of phenalenyl moieties. Calculated energy decompose analysis (EDA) shows that the orbital interaction for 22 possesses a large attractive contribution of −18.31 kcal mol–1, which is dominated by the π–π stacking interaction between the upper and the lower π-conjugated units. Interestingly, the natural population analysis (NPA) charge and the transition density matrix (TDM) show that both intramolecular charge transfer and intermolecular charge transfer (CT) exist in 22. Further, the first hyperpolarizability (βtot = 4.56 × 104 au) of 2 with intramolecular CT is greatly larger than that of reported molecule 3 (5.45 × 103 au) with intermolecular CT. Significantly, 22 exhibits the largest βtot value to be 1.42 × 105 au, which is caused by combining the intra- and intermolecular CT transitions (βx = 1.40 × 1...