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⊗e Jahn–Teller (JT) effect. Upon excitation to two lowest excited states (S1 and S2) 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 S1 state or undergo the nonadiabatic transitions between S1 and S2 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.