William R. Moomaw

Luminescence and hydrogen bonding in quinoline and isoquinoline

A purification scheme has been developed which is capable of separating the two isomers quinoline and isoquinoline. The emission spectra of the purified compounds were measured at 77 K in a 3‐methylpentane (3MP) glass and in a 3MP glass with small amounts of hydrogen bonder added. The hydrogen bonders used were hexafluoroisopropanol (HFIP), trifluoroethanol (TFE), and absolute ethanol (EtOH). An upper limit on the ratio of fluorescence to phosphorescence quantum yields has been set at 20 ppm for quinoline in 3MP, which is 1–2 orders of magnitude smaller than previously reported. Isoquinoline still fluoresces in 3MP, which we believe to be caused by a residual hydrogen bonder not removed by the purification scheme. The excitation and lifetime data obtained suggest that the phosphorescence in these compounds is originating in a nonhydrogen‐bonded species, while the fluorescence is originating in a hydrogen‐bonded species, regardless of solvent. A new emission has also been detected in the presence of small ...

The role of dπ orbitals in spin-orbit coupling

A general framework is developed for the theoretical treatment of d-orbital contributions of heavy atoms to the spin-orbit coupling of planar molecules. Unlike pπ orbitals for which only three-centre spin-orbit terms are non-vanishing, it is shown that a number of one- and two-centre terms will contribute. The case of thiophene (C4H4S) is examined, and all one- and two-centre integrals are evaluated explicitly. Although the two-centre terms are individually only a few per cent of the one-centre term, it is found that because of the large number of two-centre terms, they usually dominate the one-centre term. In thiophene, it is found that the contribution of individual dπ terms is on the order of 0·02-2·0 cm-1, which is comparable in magnitude to other contributions. An examination of the results as a function of effective nuclear charge and internuclear distance is also made.