A Window into the Workings of anti-B18H22 Luminescence-Blue-Fluorescent Isomeric Pair 3,3'-Cl2-B18H20 and 3,4'-Cl2-B18H20 (and Others)

The action of AlCl3 on room-temperature tetrachloromethane solutions of anti-B18H22 (1) results in a mixture of fluorescent isomers, 3,3'-Cl-2-B18H20 (2) and 3,4'-Cl-2-B18H20 (3), together isolated in a 76% yield. Compounds 2 and 3 are capable of the stable emission of blue light under UV-excitation. In addition, small amounts of other dichlorinated isomers, 4,4 '-Cl-2-B18H20 (4), 3,1 '-Cl-2-B18H20 (5), and 7,3'-Cl-2-B18H20 (6) were isolated, along with blue-fluorescent monochlorinated derivatives, 3-Cl-B18H21 (7) and 4-Cl-B18H21 (8), and trichlorinated species 3,4,3'-Cl-3-B18H19 (9) and 3,4,4'-Cl-3-B18H19 (10). The molecular structures of these new chlorinated derivatives of octadecaborane are delineated, and the photophysics of some of these species are discussed in the context of the influence that chlorination bears on the luminescence of anti-B18H22. In particular, this study produces important information on the effect that the cluster position of these substitutions has on luminescence quantum yields and excited-state lifetimes.

Automated summary

The reaction of AlCl3 with room-temperature tetrachloromethane solutions of anti-B18H22 resulted in the formation of fluorescent isomers, 3,3'-Cl-2-B18H20 and 3,4'-Cl-2-B18H20, with 76% yield. These isomers exhibited stable blue light emission under UV excitation. Other dichlorinated and monochlorinated derivatives, as well as trichlorinated species, were also isolated. The molecular structures and photophysical properties of these chlorinated derivatives were investigated, providing valuable insight into the effect of chlorine substitution on the luminescence of anti-B18H22.