Recognition, Sensors, and Responsive Switches

Abstract

Both the helicity and the π–conjugated structure of helicenes endow them with a wide range of potential applications in molecular recognition and fluorescent sensing, and the environmentally responsive switches, especially in the chiral recognition and chiroptical switches. Thus, chiral recognition of helicene crown ethers toward racemic amine salts, recognition of diacids by helicopodand, chiral recognition between the BINOL-modified Au nanoparticles and Helquat via donor–acceptor interactions, and chiral recognition between the helicene quinone radical anion and BINAPO were sequentially found. It was also found that stereoregular helical acetylenes with [6]helicene units as the pendants generated by Rh-catalyzed polymerization display the ability to adsorb one enantiomer preferentially in a racemic mixture solution. Moreover, 2,15-dihydroxyl[6]helicene as fluorescence sensor for chiral amines and aminoalcohols, diaza[4]helicenes with pyridine and amino moieties for pH-sensitive sensing, tetrahydro[5]helicene thioimide-based chemodosimeter for Hg2+, and a humidity sensor based on [6]helicene-derived imidazolium salt were also developed. Recently, a series of fast-responsive explosive sensors based on the polymerization of [5]helicenes were reported as well. Furthermore, helicenes and their derivatives can be applied in the design and development of various acid-base responsive switches, redox-responsive switches, photo-responsive switches, and chiroptical switches.