The Role of Charge Transfer and Parity Symmetry of the Wave Function in N,N′‑Bis(2-phenylethyl)-3,4,9,10-perylenedicarboximide Crystals: A Frenkel-Holstein Approach

Here, we develop an extended Frenkel–Holstein Hamiltonian that explicitly includes CT and intermolecular TT diabatic states. We show that site-exchange parity controls optical activity.

In the Condon limit, only the even (+) sector is bright, and TT borrows oscillator strength only through the parity-matched chain |<i>FE</i>₊⟩ →|<i>CT</i>₊⟩ → |<i>TT</i>₊⟩ off the Frenkel exciton (FE) as determined by the relative phase of the electron/hole transfer coupling <i>t</i>₊ and relative phase of the CT–TT coupling <i>g</i>_<i>+</i>. CT–TT mixing also raises the energy of the active CT state, increasing the effective FE–CT detuning and suppressing CT-mediated superexchange.