Ring-in-Ring(s) Complexes Exhibiting Tunable Multicolor Photoluminescence

Abstract

One ring threaded by two other rings to form a non-intertwined ternary ring-in-rings motif is a challenging task in noncovalent synthesis. Constructing multicolor photoluminescence systems with tunable properties is also a fundamental research goal, which can lead to applications in multidimensional biological imaging, visual displays, and encryption materials. Herein, we describe the design and synthesis of binary and ternary ring-in-ring(s) complexes, based on an extended tetracationic cyclophane and cucurbit[8]­uril. The formation of these complexes is accompanied by tunable multicolor fluorescence outputs. On mixing equimolar amounts of the cyclophane and cucurbit[8]­uril, a 1:1 ring-in-ring complex is formed as a result of hydrophobic interactions associated with a favorable change in entropy. With the addition of another equivalent of cucurbit[8]­uril, a 1:2 ring-in-rings complex is formed, facilitated by additional ion–dipole interactions involving the pyridinium units in the cyclophane and the carbonyl groups in cucurbit[8]­uril. Because of the narrowing in the energy gaps of the cyclophane within the rigid hydrophobic cavities of cucurbit[8]­urils, the binary and ternary ring-in-ring(s) complexes emit green and bright yellow fluorescence, respectively. A series of color-tunable emissions, such as sky blue, cyan, green, and yellow with increased fluorescence lifetimes, can be achieved by simply adding cucurbit[8]­uril to an aqueous solution of the cyclophane. Notably, the smaller cyclobis­(paraquat-p-phenylene), which contains the same p-xylylene linkers as the extended tetracationic cyclophane, does not form ring-in-ring(s) complexes with cucurbit[8]­uril. The encapsulation of this extended tetracationic cyclophane by both one and two cucurbit[8]­urils provides an incentive to design and synthesize more advanced supramolecular systems, as well as opening up a feasible approach toward achieving tunable multicolor photoluminescence with single chromophores.

Supramolecular Chemistry: Host–Guest Molecular Complexes

“…Thus, covalent polymers associated via non-covalent interactions establish supramolecular polymer networks resulting in self-assembled materials having assemblage stability, recyclability, processability, incentives response, or self-restorative ability [ 95 ]. The fabrication of ring-in-ring(s) composites displays adjustable multicolor photoluminescence due to hydrophobic interactions linked with a specified entropy change directed to practical applications such as visual displays or multidimensional biological imaging [ 96 ]. Many practical, applicable HG relations were recently explored by different research groups, such as HG relation of perethylated Pillar[6]arene with ferrocene derivatives [ 97 ].…”

A contorted nanographene shelter

“…6g ) to a yurt-like shape, in which one of the TPAP units bulges outwards. These observations are reminiscent of the induced fit of enzymes with respect to their substrates in biological systems 65 , 66 .…”

Confined Spaces in [n]Cyclo‐2,7‐pyrenylenes

“…Host-in-host complexes are an intriguing starting point in the construction of more complex superstructures. [65][66][67] A well-studied example is the encapsulation of crown ethers or their nitrogen-containing equivalents into cages or capsular hosts. [68][69][70][71][72] We selected crown ethers as guests because they are conformationally flexible allowing them to pass the gate of the macrocycle, and being readily available in various sizes.…”