Macrocyclic hosts capable of specific molecular recognition are crucial for advancing supramolecular chemistry, but rarely display phosphorescent activity. Herein, we report a new class of macrocycles, iminodibenzyl[n]arenes (IB[n]As, n = 3, 4), that exhibit unusual green room-temperature phosphorescence (RTP). The uniqueness of IB[4]A is a concave double-cavity structure with an RTP lifetime of 3.82 ms. Although IB[3]A has a shorter RTP lifetime of 1.91 ms, it features outstanding size-selective binding for guest molecules due to its tendency for prismatic cavity formation. This was supported by single-crystal analysis, density functional theory calculations, and host-guest binding experiments involving eight different-sized cationic guests. The structural complementarity between IB[3]A and 1,4-diazabicyclo[2.2.2]octane cation G4 is particularly notable, affording a stronger affinity (K = 2524 M−1) compared to others. Accordingly, encapsulating this suitable “guest rivet” induces a more rigid microenvironment, prolonging the RTP lifetime to 8.99 ms. This study bridges selective molecular recognition and RTP modulation in macrocyclic hosts, facilitating the architectural design of complex molecules and offering diverse post-synthetic tunability for phosphorescent compounds.
