Naphthols 5,8-dicyano-2-naphthol

Naphthols with electron-withdrawing groups such as cyano sulfonyl and methanesulfonyl at C-5 and C-8 exhibit greatly enhanced photoacidity [48], 5,8-dicyano-1-naphthol shows remarkable photoacidity with a pKa of 7.8 and a Forster cycle pK a of -4.5. The kinetics and mechanism of ESPT of these superphotoacid molecules have been subjected to extensive investigations in recent times [49-53],... 

The diazotization products of 2- and 4-aminophenols, -naphthols (etc.), possess a mesomeric (zwitterionic) phenolate-diazonium and quinone-diazide structure. We discussed these structures in the context of aromatic diazotization (Zollinger, 1994 Sect. 2.4) because the synthetic methods used are closely related to those used for aromatic diazonium salts. This is also the case for the diazotization of amino-di-, tri- and tetrazoles, which, in their neutral form, contain a heterocyclic NH group in the )8-position to the amino group. After diazotization, the NH group is very acidic. Following deprotonation the product corresponds to a heterocyclic diazoalkane. Similarly, the diazotization product of 4-(dicyano)methylaniline ((4-amino-phenyl)malonitrile) may lose the CH proton. This compound is, therefore, sometimes called a vinylene homolog of diazomalonitrile (Regitz and Maas, 1986, p. 205). 

Naphthols with electron-withdrawing substituents such as cyano at C5 and C8 exhibit even more enhanced acidities in their excited singlet states and are capable of proton transfer to solvents such as alcohols in the absence of water. For example, the acidity of 5,8-dicyano-2-napththol increases from 7.8 in the ground state to -4.5 in the excited singlet state. Tolbert, L. M. Haubrich, J. E. /. Am. Chem. Soc. 1994, 316,10593 Tolbert, L. M. Solntsev, K. M. Acc. Chem. Res. 2002, 35,19. 

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