Orbital degeneracy in π molecular conductors: A target in the next decade

By the end of the 20th century, the research of electromagnetic behavior of π-electrons in organic crystals made several outstanding achievements. Since 50’s, the epoch-making finding appeared every decade: enhanced conductivity in halogen complexes of aromatic hydrocarbons 1) (1954), highly conductive radical salts of a π-acceptor TCNQ 2) (1960), a charge transfer complex TTF-TCNQ with quasi-one-dimensional metallic behavior 3) and charge density waves (CDW) (1973), the organic superconductors (TMTSF)2X and spin density waves (SDW) 4) (1980), the first purely organic ferromagnet β-p-NPNN 5) and superconductivity in C60 salts 6) (1991). In 2001, superconductivity induced by strong magnetic field 7) and those induced by carrier injection into an organic FET 8) were reported. Almost all the basic phases in solid state physics have been, thus, established in organic crystals. This doubtlessly owes much to the developments of synthetic chemistry providing new molecular designs and to the many efforts to control molecular arrangements in crystals.