,Spectroscopic Characteristics and Photochemical Studies of Some Mercocyanin –like Azole dye

Abstract

A senes of 7-Arylhydrazono-5H-[1,2,4]triazolo[3,4-b][1,3,4] t. thiadiazines were synthized by the reactions of 4-amino-5-phenyl-4H- [1,2,4]triazolo-3-thiol bromides ( Scheme 1 ) and 2-(2-naphthyl)-2-oxoethanehydrazonoyl N-N Ar N-N HN RCOC(X):NNHAr + Ph Nj(_SH I 1 NH2 2 -HX II II I Ph /'-.._s-\N NH2 -f-R 3 0 4A 48 X = Br or Cl; Ph = C6H5 ; R = 2-naphtbyl Ar = ZC6H4 ; Z : a, 4-MeO; b, 4-Me; c, 3-Me; d, H; e, 4-Cl; f, 3-Cl; g, 3-N02 ; b, 4-MeCO; i, 4-EtOCO; j, 4-N0 2 Scheme 1 The UV and NMR and absorption spectra of the studied compounds indicate that they exist predominately in the hydrazone tautmeric form 4A. this conclusion was confirmed by measurement of their acid dissociation constants pK, pK* in the ground and excited states, respectively and correlating these data with Hammet equation . Both pK, ._ pK* data were found to be better correlated with enhanced crx- constants.