Synthesis of the precursor to this polyradical was carried out by Kan Lu, a master student. In fact, the synthesis was earlier attempted by a postdoc. Definitely, this was a very difficult synthesis.
The design of annelated macrocycles was to provide multiple spin coupling paths, therefore, should help alleviating the problem with the defects. However, the outcome was a bit disappointing; only S = 6.2 was obtained (value of S = 7 was expected). Quenching studies suggested that only 12 - 13 unpaired electrons were generated. Moreover, the ferromagnetic coupling between these unpaired electrons was relatively weak, compared to that of typical 1,3-phenylene-based polyarylmethyl, presumably due to the out-of-plane distortion of the π-conjugated system. It was suspected that the problem were mainly at the two most inner sites, connecting the two calixarene rings.
- A. Rajca, K. Lu, S. Rajca, "High-Spin Polyarylmethyl Polyradical: Fragment of a
Macrocyclic 2-Strand Based upon Calixarene Rings", J. Am. Chem. Soc.,
1997, 119, 10335.
With persistent of the defect(s) in the annelated polyarylmethyl polyradicals, it was realized that very high-spin organic molecules could not be prepared by the simple approach, i.e. alternating connection of spin coupling units and spin sites. To solve this problem, we came up with the organic spin cluster approach, which leaded to the S = 10, dendritic macrocyclic polyarylmethyl polyradical and many other very high-spin molecules and polymers, including the S = 5000 polymer with magnetic ordering.
- A. Rajca, J. Wongsriratanakul, S. Rajca, R. Cerny, "Dendritic-Macrocyclic
Very-High-Spin Organic Polyradical with S = 10", Angew. Chem. Int. Ed.,
1998, 37, 1229.
- A. Rajca, J. Wongsriratanakul, S. Rajca, "Magnetic Ordering in an Organic Polymer", Science, 2001, 294, 1503.
- S. Rajca, A. Rajca, J. Wongsriratanakul, P. Butler, S. Choi, "Organic Spin Clusters. Dendritic-Macrocyclic Polyarylmethyl Polyradical with Very High-Spin of S = 10 and its Derivatives: Synthesis, Magnetic Studies, and Small Angle Neutron Scattering" J. Am. Chem. Soc., 2004, 126, 6972.
- A. Rajca, J. Wongsriratanakul, S. Rajca, "Organic Spin Clusters: Macrocyclic-Macrocyclic Polyarylmethyl Polyradicals with Very High-Spin S = 5 - 13", J. Am. Chem. Soc., 2004, 126, 6608.
- A. Rajca, J. Wongsriratanakula, S. Rajca, R. L. Cerny, "Organic Spin Clusters: Annelated Macrocyclic Polyarylmethyl Polyradicals and Polymer with Very High-Spin S = 6 - 18", Chem. Eur. J., 2004, 10, 3144. (VIP)