Scientists in Japan have developed the size-selective syntheses of the four “missing” cycloparaphenylenes (CPP) (, ,  and ), which complete the sequence of -CPP. It is important to have access to all of the CPPs in pure form for their future applications and for ring-size effect studies. The synthesis of CPPs was only recently realised (in 2008) and these molecules could find significant utility in supramolecular chemistry and materials science.
Link to journal article
Size-selective synthesis of - and cycloparaphenylenes
Y Ishii et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20343j