Naphth[4]arene: Synthesis, Conformations, and Application in Color-Tunable Supramolecular Crystalline Assemblies

Although the chemistry of macrocyclic arenes has seen rapid development in recent years, the synthesis of new macrocyclic arenes from aromatic rings with no directing groups remains a challenge. In this work, a new macrocyclic arene, naphth[4]arene (NA[4]A), composed of four naphthalene rings bridged by methylene groups, was synthesized using macrocycle-to-macrocycle conversion. NA[4]A shows 1,3-alternate and 1,2-alternate conformations in the solid state, which can be selectively obtained. By supramolecular co-assembly of NA[4]A and 1,2,4,5-tetracyanobenzene (TCNB) in different concentrations and temperatures, two conformation-dependent crystalline luminescent co-assemblies 1,2-NTC and 1,3-NTC can be selectively prepared. Interestingly, the two charge-transfer crystalline assemblies containing NA[4]A with different conformations show bright yellow and green fluorescence, and also display high photoluminescence quantum yields (PLQYs) of 45 % and 43 %. Furthermore, they exhibit color-tunable two-photon excited upconversion emission.

Automated summary

Despite the advances in the chemistry of macrocyclic arenes, synthesizing new macrocyclic arenes from aromatic rings without directing groups remains difficult. However, this study successfully synthesized a new macrocyclic arene, naphth[4]arene (NA[4]A), through macrocycle-to-macrocycle conversion. NA[4]A displayed two distinct conformations in solid state and could be selectively obtained. By co-assembling NA[4]A with 1,2,4,5-tetracyanobenzene (TCNB) at different concentrations and temperatures, two conformation-dependent crystalline luminescent co-assemblies, 1,2-NTC and 1,3-NTC, were selectively prepared. Notably, these assemblies exhibited bright fluorescence, high photoluminescence quantum yields, and color-tunable two-photon excited upconversion emission.