Efficient Two-Photon Excited Fluorescence from Charge-Transfer Cocrystals Based on Centrosymmetric Molecules

Two-photon excited chromophores are widely applied for photon upconversion in organic optoelectronics. In this work, efficient two-photon excited fluorescence is observed from charge-transfer cocrystals where the molecular architectures of donor and acceptor molecules are both centrosymmetric. The superior structural symmetry of cocrystals eliminates the second harmonic generation of incident near-infrared laser. The nonlinear optical properties of cocrystals are found to be strongly correlated with the intermolecular charge-transfer interaction, bringing a wide window of excitation wavelength for the upconverted light emission. The work demonstrates that the cocrystallization of small molecules provides opportunities for the design and synthesis of novel organic optofunctional materials.