We synthesized a series of 1,4,7,10-tetraalkyltetracenes using a new 2,6-naphthodiyne precursor and 2,5-dialkylfurans as starting materials (alkyl=methyl to hexyl). Surprisingly, the solid-state color of the tetracenes ranges through yellow, orange, and red. Both yellow and red solids are obtained for the butyl derivative. Optical properties in solution show no marked differences; however, those in the solid state show characteristics that vary with alkyl side-chain length: methyl, propyl, and pentyl derivatives are orange; ethyl and butyl derivatives are yellow; and another butyl and hexyl derivative are red. X-ray analyses reveal that the molecular structures are planar, semi-chair, or chair forms; the chair form takes a herringbone-like arrangement and the other forms take slipped parallel arrangements. The mechanism of crystallochromy is discussed in terms of molecular structure, crystal packing, and calculations that take account of exciton coupling.

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We prepared 2,3-dialkyl- and 2,3,8,9-tetraalkyltetracenes by way of Diels–Alder reactions between 1,4-anthraquinones and 3,4-dialkylthiophene-1,1-dioxides and obtained mainly orange and yellow solids, respectively. The differences in optical properties in the solid state were probably due to different intermolecular interactions.

A clear phase separation into liquid iron-rich and copper-rich alloys was observed when a mixture of Fe, Cu and P was melted in an alumina or carbon crucible at 1373 K. Since this phase separation is considered to be useful for recovering valuable copper from iron-base alloy scraps, the phase equilibrium in the Fe-Cu-P and Fe-Cu-P-C systems was investigated in this study. The effect of carbon to the phase separation was determined in the concentration range of phosphorous between 7 and 11 mass% at 1373 K. It was found that the addition of carbon enlarged the miscibility gap of the Fe-Cu-P system. Distribution ratios of some minor elements of Au, Ag, Pd, Pt, Rh, Cr, Mn and Ni between the liquid iron-rich and copper rich phases were also measured at 1373 K. It was found that Au, Ag and Pd were enriched in the copper-rich phase, while Pt and Mn were distributed in both phases, and Rh, Cr and Ni preferentially in the iron-rich phase.