Fig. 1. Schematic diagram of the intermolecular electronic coupling in the crystalline state for persistent RTP: (left) chemical structure of the compound CX, (above right) intermolecular n- and π-units stacked in the crystal, and (below right) hybrid intersystem crossing formation. 
= the ground state, 
= the lowest singlet excited state, and 
= the lowest triplet excited state. All these states refer to the proposed intermolecular electronically coupled states.
