Cocrystallization-Induced Similar Red Emission in Pyrene Derivative: Unraveling the Underlying Mechanistic Divergence

Cocrystal engineering, with a simple preparation process and easily regulated excited states, provides a favorable method to realize red-emissive materials. In this contribution, we successfully prepared two kinds of red-emissive cocrystal materials by different photoluminescence mechanisms upon 1-(3,5-dimethoxyphenyl)pyrene (DMeOPPy) and 1,2,4,5-tetracyanobenzene (TCNB)/1,3,5-trifluoro-2,4,6-triiodobenzene (TFTIB). In the case of DMeOPPy-TCNB, a strong charge transfer interaction is introduced, and the emission is from the newly formed low-energy lowest singlet excited state (S₁). In contrast, for DMeOPPy-TFTIB, because of the synergistic effects of the heavy atom effect and multiple intermolecular interactions, the luminescence arises from the lowest triplet excited state (T₁). Significantly, the proximity of the S₁ and T₁ energy levels endows the two cocrystals with a similar luminescence color (λ_max = 628 nm for DMeOPPy-TCNB, λ_max = 632 nm for DMeOPPy-TFTIB, respectively). The results not only provide design strategies for the development of red-emissive cocrystal materials but also help us to deepen the understanding of excited-state modulation in luminescent materials.