Photoinduced Excited-State Energy-Transfer Dynamics of a Nitrogen-Cored Symmetric Dendrimer: From the Perspective of the Jahn-Teller Effect

We report an interesting view to understand the ultrafast excited-state energy-transfer (EET) process in the D-3-symmetric dendrimer tris(4-ethynylphenyl)amine (TEPA) from the perspective of the well-known E circle times e Jahn-Teller (JT) effect. Upon excitation to two lowest excited states (S-1 and S-2) with doubly degenerate E symmetry, two sets of e vibrational modes, dihedral angle twist and strong pyramidalization near the nitrogen core, lead to the JT distortion and symmetry lowering. Through the excited-state dynamics simulation with the on-the-fly surface-hopping approach at the TDDFT level, we find that the system may either travel three equivalent minima of S-1 state or undergo the nonadiabatic transitions between S-1 and S-2 states. These motions induce the ultrafast EET among different branches and the reorientation of the transition dipole moments, finally leading to the ultrafast fluorescence anisotropy decay. This energy-transfer mechanism can provide some interesting insights on the excited-state dynamics of large dendrimers with three equivalent branches and transition metal complexes with C-3 symmetry.