Ag(I) Controlled Encapsulation of a Naphthalene Diimide guest into Porphyrin Containers: a Photophysical Study

Guest encapsulation inside the cavity of three-dimensional structures is a phenomenon of great interest in supramolecular chemistry. The new properties that emerge from this close association can lead to applications in many areas of chemical, biological and material sciences. Guest complexation can also be controlled by external stimuli, such as photons, electrons or chemical entities, that, interacting with specific sites of the host, induce large and reversible modifications to its structure. Such control is reminiscent of the allosteric regulation used by many biological systems. Following this idea, we were interested in studying the inclusion of N,N'-dibutyl-1,4,5,8-naphthalene diimide (NDI) into molecular cages consisting of two Zn(II)-porphyrins connected by four flexible linkers of different lengths, endowed with triazole binding sites (Figure 1). We could demonstrate that the NDI guest is included in the cages only when they are in an open conformation, triggered by the binding of silver(I) ions to the lateral triazoles. The Zn-porphyrin fluorescence is quenched by an efficient photoinduced electron transfer process between the cage porphyrin and the included NDI guest. We present here the photophysical study that, combined with a detailed computational approach, allowed us to provide a reliable model for the NDI-cage complexation mechanism and the corresponding electron transfer reaction, attesting the allosteric control exercised by silver(I) ions over both processes.