Beyond Clar: The use of modern analytical tools for large PAHs

The classic work on large PAHs by Erich Clar, described in his two-volume b ook 'Polycyclic Hydrocarbons', still stands as the penultimate work in that field. Although the volumes are well over 30 years old, and cover work done in the prior three decades, work since then in the area of large PAHs has been sp oradic and nowhere near as far flung as Clar's. There has been progress, however, in various areas of analytical chemistry that extends information first found by Clar. For example, modern separatio n methods, like HPLC, can isolate certain isomers that Clar was unable to s eparate. Spectroscopic techniques, in combination with these, extend the wa velength range of fluorescence and UV absorbance spectra of large PAHs. Several examples from the peropyrene family of large PAHs will be given to illustrate the advantages gained through the use of modern analytical metho ds. These include lower wavelength spectra for violanthrene, isoviolanthren e, and other sparingly soluble large PAHs; the first direct spectra of cert ain compounds that were previously only obtained through subtraction, and i dentification of some isomers that were present in Clar's reaction mixtures but that he did not find with the techniques available to him at the time.