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 (λmax = 628 nm for DMeOPPy-TCNB, λmax = 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.