Photophysical Characterizationof a Benzo-Fused Analogueof Brooker’s Merocyanine: Solvent Polarity and pH Effects.

The photophysical properties of 4-[2-(6-hydroxy-2-naphthalenyl)-ethenyl]-1-methyl-pyridinium(HNEP+) and its deprotonatedform (NEP), a benzofused derivative of Brooker’smerocyanine (BM), were investigated through a combinedspectroscopic and computational approach. Despite their structuralsimilarities and similar pKavalues, HNEP+/NEPand BMH+/BMdiffer in the extent ofcharge delocalization in the ground and excited states. NEPexhibits the spectral characteristics of a charge transfer speciesin solvents in which BMexists in a charge-delocalizedquinoid; however, quantum chemical calculations show that the CT absorptionof NEPis not necessarily a consequence of the zwitterioniccharacter. HNEP+displays largerStokes shifts than BMH+, and NEPdemonstrates enhanced solvatochromism relative to BMas a consequence of benzofusion. [ABSTRACT FROM AUTHOR]