Donor−Acceptor-Substituted Anthracene-Centered Cruciforms: Synthesis, Enhanced Two-Photon Absorptions, and Spatially Separated Frontier Molecular Orbitals

This paper reports the design, synthesis, two-photon absorption (TPA) properties, and frontier molecular orbital (FMO) features of a new class of cruciforms. These new cruciforms utilize the anthracene ring as a π-center and exhibit very large and significantly enhanced two-photon absorption cross sections (δ) that are two to four times as large as the sum of the δ values of the two corresponding linear analogues over a relatively wide range of wavelengths (740−900 nm). Quantum chemical calculations and solvatochromic behaviors reveal that donor−acceptor-substituted anthracene-centered cruciforms show spatially separated HOMO and LUMO. Although the enhancement of δ in anthracene-centered cruciforms seems to be not relative to their FMO features, this is thoroughly different from the known characteristics of benzene-centered analogues showing no enhancement of δ. On considering that the only difference in these cruciforms is the π-center, it is primarily concluded that the anthracene core plays a crucial role in the enhancement of δ.