title: Tautomerism of 4,4'-dihydroxy-1,1'-naphthaldazine studied by experimental and theoretical methods.
abstract: BACKGROUND
  The title compound belongs to the class of bis-azomethine pigments. On the basis of comparative studies on similar structures, insight into the complex excited state dynamics of such compounds has been gained. It has been shown, for example, that only compounds that possess hydroxyl groups are fluorescent, and that the possibility for cis-trans isomerisation and/or bending motions of the central bis-azomethine fragment allows for different non-radiative decay pathways.
  
  
  RESULTS
  The compound, 4,4'-dihydroxy-1,1'-naphthaldazine (1) was synthesized and characterized by means of spectroscopic and quantum chemical methods. The tautomerism of 1 was studied in details by steady state UV-Vis spectroscopy and time resolved flash photolysis. The composite shape of the absorption bands was computationally resolved into individual subbands. Thus, the molar fraction of each component and the corresponding tautomeric constants were estimated from the temperature dependent spectra in ethanol.
  
  
  CONCLUSIONS
  According to the spectroscopic data the prevalent tautomer is the diol form, which is in agreement with the theoretical (HF and DFT) predictions. The experimental data show, however, that all three tautomers coexist in solution even at room temperature. Relevant theoretical results were obtained after taking into account the solvent effect by the so-called supermolecule-PCM approach. The TD-DFT B3LYP/6-31 G** calculated excitation energies confirm the assignment of the individual bands obtained from the derivative spectroscopy.
authors: Institute of Organic Chemistry with Centre of Phytochemistry Bulgarian Academy of Sciences, Acad, G, Bonchev str,; bl,9, Sofia, BG-1113, Bulgaria. lantonov@orgchm.bas.bg.
authors: Anife
authors: A
authors: Ahmedova
authors: Svilen P
authors: SP
authors: Simeonov
authors: Vanya B
authors: VB
authors: Kurteva
authors: Liudmil
authors: L
authors: Antonov
references: J Phys Chem A. 2007 Nov 1;111(43):10891-8
references: 17918808
references: Ultrason Sonochem. 1998 Nov;5(3):107-11
references: 11270343
references: Anal Bioanal Chem. 2002 Dec;374(7-8):1312-7
references: 12474103
references: Angew Chem Int Ed Engl. 2005 Dec 2;44(47):7783-6
references: 16315162
references: Phys Rev B Condens Matter. 1988 Jan 15;37(2):785-789
references: 9944570
references: Environ Sci Technol. 2004 Sep 15;38(18):4856-9
references: 15487796
references: Comput Chem. 2000 Jul;24(5):561-9
references: 10890365
references: Photochem Photobiol Sci. 2007 Jan;6(1):50-6
references: 17200736
references: Phys Chem Chem Phys. 2006 Mar 14;8(10):1197-204
references: 16633600
references: Phys Chem Chem Phys. 2005 Sep 21;7(18):3297-305
references: 16240044