Near-Infrared-Excitable Organic Ultralong Phosphorescence through Multiphoton Absorption
Molecular design strategy of MPA-OURTP materials. (a) Exciton transformation pathways of one-photon- (OPA), two-photon- (TPA), and three-photon- (3PA) triggered OURTP. The ground state (S0) molecule can be excited to S by absorption of one, two, or three photons and then fall to S1 through IC for fluorescence (Fl.). The triplet excited state (T) can be populated from S1 via ISC, and the radiative decay of the lowest T (T1) leads to phosphorescence (Phos.), while by further stabilization for T, OURTP is produced. (b) Design of MPA-OURTP molecules in a D-A-D architecture with strong and abundant in-plane (dashed black) and interlayer (red line) intermolecular interactions in crystal. (c, d) Schematic drawing of (c) MPA-OURTP molecules using a planar -conjugation donor and a difluoroboron β-diketonate acceptor with synergistic effects of intramolecular CT (ICT) and intermolecular space CT (SCT) for MPA and (d) the molecular structure of the designed model compound of CzPAB.