| Abstrakt: |
9-Arylxanthen-9-ylium (3a–i) and 9-arylthioxanthen-9-ylium (4a,b,e–i) perchlorates [aryl = 2,4,6-(MeO)3C6H2(a), 2,6-(MeO)2C6H3(b), 2-MeOC6H4(c), 4-MeOC6H4(d), 3-Br-2,6-(MeO)2C6H2(e), 2,4,6-Me3C6H2(f), 2-MeC6H4(g), 4-MeC6H4(h), C6H5(i)] were prepared by the reactions of 9-arylxanthen-9-ols or 9-arylthioxanthen-9-ols with perchloric acid. Their LUMO and HOMO levels were estimated from the redox potential (E0) in cyclic voltammetry and λmaxin the UV–visible spectra measured for a 1,2-dichloroethane solution, and were compared with those of 9-aryl-1,8-dimethoxyxanthen-9-ylium ions (8b,i). We found that 1) both the LUMO and HOMO levels varied almost in the same order of substituent on the 9-phenyl group; 2) the MeO-group on the 9-phenyl group was more effective to raise both the HOMO and LUMO levels than the Me-group; 3) the HOMO levels of 3and 4were more sensitive than the LUMO levels to the change in the 9-aryl group; 4) p-substitution by MeO- or Me-groups was more effective to raise the HOMO and LUMO levels than o-substitution; 5) the presence of two o-MeO groups was more effective to raise the HOMO and LUMO levels than one o-MeO group; 6) a m-bromination of 9-aryl group in 3bor 4bgreatly lowered both LUMO and HOMO levels, as observed for 3eor 4e; 7) both the HOMO and LUMO levels of 8band 8iwere higher than those of 3band 3i, respectively; 8) the LUMO level of 3bwas higher than that of 8i, the isomer. |
