A Tetra‐Armed Cyclen With Biphenyl Side Arms: Silver(I) Binding Enables Longer‐Wavelength Detection of Guest Chirality

Longer‐wavelength chiroptical detection is desirable for chiral compounds that show weak intrinsic circular dichroism (CD) responses in the short‐wavelength UV region. A new tetra‐armed cyclen ligand L with biphenyl side arms was prepared to shift guest‐induced chiroptical responses to longer wavelengths. The ligand showed argentivorous behavior toward Ag(I), and single‐crystal X‐ray diffraction revealed that the four aromatic side arms form a pseudo‐cavity around the Ag(I) center. The structure of CH 3 CN⊂L·AgOTf further demonstrated the inclusion of a nitrile guest in this cavity. The absorption maximum of L·Ag + appeared at around 280 nm, compared with approximately 250 nm for the previously reported styrylmethyl analog L St ·Ag + . Chiral nitriles and amines induced characteristic Cotton effects at 296–298 nm in the L·Ag + system, approximately 38 nm longer than those of L St ·Ag + . The p ‐dimethylamino‐substituted analog L Dma ·Ag + showed still longer‐wavelength responses at 307–335 nm. The CD intensity of L·Ag + at 298 nm also showed good linear relationships with the enantiomeric excess of both nitrile and amine guests. These results demonstrate that modification of the chromophoric side arms of argentivorous cyclens enables longer‐wavelength detection of guest chirality while retaining guest‐to‐host chirality transfer.