On the Anomalous Absorption Spectra of Amino- and Hydroxy-Substituted Anthracenes

It has been known for some time that the longest wavelength absorption band of anthracene arises from the transversely polarized 1 L a ← 1 A absorptive transition (1). The angular momentum forbidden 1 L b ← 1 A transition, which is invariably at least ten-fold weaker than the former transition in the acenes has been predicted, on theoretical grounds, to be submerged in the 1 L a ← 1 A absorption envelope (2). That the 1 L b ← 1 A transition of anthracene does not lie much higher in energy than the 1 L a ← 1 A transition was demonstrated by Baba and Suzuki (3) who proved that although the long-wavelength absorption band of 1-anthrol originated from the 1 L a ← 1 A absorption, as anticipated, the long-wavelength absorption bands of 2-anthrol and its conjugate anion originated from the admixture of charge-transfer from the β-hydroxy group into the longitudinally polarized 1 A ← 1 L b transition of anthracene.