Fig. 1. Portions of (a) HPLC/UV and (b) HPLC/MS chromatograms, from 70 to 90 min, showing the retention times of the four C₂₈H₁₄ products of supercritical toluene pyrolysis at 585 °C, 110 atm, and 140 s residence time. Benzo[a]coronene and phenanthro[5,4,3,2-efghi]perylene coelute at 79.1 min; compound I elutes at 79.8 min; benzo[pqr]naphtho[8,1,2-bcd]perylene elutes at 82.1 min. Molecular structures in (a) correspond to the C₂₈H₁₄ compounds unequivocally identified [6] in the product mixture. The MWs of these isomers and compound I, as well as those of other nearby-eluting product components, appear as peak labels in (b). The ascent in the baseline in (a) is due to an increase of UV-absorbing benzene in the mobile phase composition, in accordance with the HPLC solvent program.

Fig. 2. The mass spectrum of compound I, the product component eluting at 79.8 min in Fig. 1.

Fig. 3. UV absorbance spectra for (a) benzo[ghi]perylene in acetonitrile; (b) dibenzo[b,ghi]perylene in ethanol (before 280 nm) and benzene (after 280 nm) [15]; and (c) compound I in 25:75 acetonitrile:DCM. The structures of these compounds are shown at the right of the UV spectra. The structures in (a) and (b) are from the respective reference standards; the bracketed structure shown in (c) is that deduced in this paper for compound I.

Fig. 4. The structures of dibenzo[cd,lm]perylene (II), tribenzo[a,cd,lm]perylene (III), and benzo[cd]naphtho[1,2,3-lm]perylene (IV). The wavelengths of maximum absorbance for the terminal β- and p-band peaks, λ_β and λ_p, respectively, for each PAH are given below their structures.

Fig. 5. The structures of tetrabenzo[a,cd,j,lm]perylene (V), dibenzo[j,lm]phenanthro[5,4,3-abcd]perylene (VI), and diphenanthro[5,4,3-abcd:5′,4′,3′-jklm]perylene (VII). The wavelengths of maximum absorbance for the terminal β- and p-band peaks, λ_β and λ_p, respectively, for each PAH are given below their structures.

Fig. 6. The structures of dibenzo[cd,lm]perylene (II), tribenzo[cd,ghi,lm]perylene (VIII), and dibenzo[bc,kl]coronene (IX). The wavelengths of maximum absorbance for the terminal β- and p-band peaks, λ_β and λ_p, respectively, for II and IX are given below their structures.

Fig. 7. The UV spectra for (a) dibenzo[cd,lm]perylene in benzene and (b) dibenzo[bc,kl]coronene [11], in 1-methylnaphthalene.

Fig. 8. The structures of pyrene (X), anthanthrene (XI), and naphthaceno[3,4,5,6,7-defghij]naphthacene (XII). The wavelengths of maximum absorbance for the terminal β- and p-band peaks, λ_β and λ_p, respectively, for X and XI are given below their structures.

Fig. 9. The UV spectra for (a) pyrene in acetonitrile–water and (b) anthanthrene in acetonitrile from our UV spectral library.

Fig. 10. The structures of benzo[ghi]perylene (XIII), dibenzo[b,ghi]perylene (XIV), benzo[ghi]naphtho[8,1,2-bcd]perylene (XV), and dibenzo[e,ghi]perylene (XVI). The wavelengths of maximum absorbance for the terminal β- and p-band peaks, λ_β and λ_p, respectively, for XIII, XIV, and XVI are given below their structures.

Fig. 11. Reaction pathways [16] in the supercritical pyrolysis of toluene, showing the formation of PAH from the addition of methyl (dashed arrow), benzyl (solid arrow), and phenyl radicals (dashed-dotted arrow). Dehydrogenation is shown as the double-lined arrow. In general, the three types of reactions are: (A) addition of methyl followed by benzyl; (B) addition of phenyl; and (C) addition of two methyls. Product components identified by matching UV spectra with those of reference standards or published in the literature are shown in bold print. Benzo[ghi]naphtho[8,1,2-bcd]perylene is shown as the boxed structure.

C₂₈H₁₄ benzenoid PAH structures and length-to-breadth (L/B) ratios