Pyronine ring

In pyronines, replacement of the carbon atom of the central ring (opposite to the oxygen atom) by a nitrogen atom produces oxazine dyes, which are used as laser dyes emitting in the range 600-750 nm. 

The phthaleins derived from di- or polyhydric phenols are all anhydrides formed by the elimination of water from two phenolic hydroxyls, attached to two different benzene rings. These anhydride phthaleins are known as pyronines, since they contain, like the pyrones, a six-membered oxygen-containing ring. 

Figure 9,11 Framework structure of zeolite L. (a) Projection along the c axis (b) projection perpendicular to the main channel direction, with A-E representing the positions of the cations (c) 12-membered-ring main channel (d) scanning electron microscopoe image of zeolite L crystals (e) structures of pyronine (left) and oxonine (right). Reproduced with permisson from [66], Copyright (2003) Wiley-VCH...

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