Synthesis of a Rhodamine-Appended Cyclophane as a Fluorescence Host in Water

Abstract

A cationic water-soluble cyclophane (1a) having a rhodamine moiety as a red-fluorescence fluorophore was prepared by reaction of a monoamine derivative of tetraaza[6.1.6.1]paracyclophane having three N-t-butoxycarbonyl-β-alanine residues with rhodamine B isothiocyanate, followed by removal of the protecting groups. The guest-binding behavior of 1a toward anionic guests such as dabsyl derivative and 4-(1-pyrene)butanoate was investigated by fluorescence spectroscopy. The results suggested the formation of host-guest complexes with a stoichiometric ratio of 1:1 and the binding constants (K) of the host-guest complexes were evaluated.

Fluorescent cyclophanes and their applications

“…The same cyclophane with other appended fluorophores, i.e. , pyrene, 49 and rhodamine, 50 have also been designed and synthesized. It is worth highlighting that these anionic cyclophanes have their cationic analogues when the side chains are terminated with ammonium ions.…”

“…Furthermore, this cyclophane forms 48 moderately stable hostguest complexes, which modify the emissive properties of the ring, with naphthalene-2-sulfonate derivatives and myoglobin. The same cyclophane with other appended fluorophores, i.e., pyrene, 49 and rhodamine, 50 have also been designed and synthesized. It is worth highlighting that these anionic cyclophanes have their cationic analogues when the side chains are terminated with ammonium ions.…”

“…Following this pioneering work, other fluorophores, such as pyrenes, 121 BODIPYs, 122 rhodamines, 123 anthracenes, 53 2-amino-124 or 2-mercapto-benzothiazole, 125 amongst others (Fig. 7b, 12b-f) were attached as pendant units onto the cyclophane's skeleton (20,(47)(48)(49)(50)(51). The possible applications of such fluorescent macrocycles are diverse.…”