Photophysical Modulation of an Elongated Ir(III) Complex by a Resorcin[4]arene Monomer Host

Molecular recognition of guest molecules within confined cavities enables effective modulation of their chemical and physical properties through noncovalent interactions. Because these modulated properties reflect the structural features of the host–guest assembly, the guest molecule can serve as a molecular probe to elucidate the origin of the host‐induced modulation. Herein, we report the formation of a host–guest complex composed of an emissive Ir(III) complex salt and a resorcin[4]arene host, along with the photophysical modulation of the guest via noncovalent interactions with the host. NMR spectroscopic analysis reveals a 1:1 binding stoichiometry, in contrast to the previously reported 6:1 stoichiometry, because the guest is larger than the cavity of the resorcin[4]arene hydrogen‐bonded hexameric capsule. This 1:1 binding mode is unambiguously confirmed by single‐crystal X‐ray diffraction analysis. The photoluminescent properties of the Ir(III) complex are enhanced in the presence of the host, indicating that electronic communication between the host and the guest plays a crucial role in modulating its photophysical behavior. These findings are further supported by density functional theory calculations. Overall, this article provides new insights into the photophysical dynamics of entrapped emitters and highlights the pivotal role of host–guest interactions in tuning emission properties.