Thiosemicarbazones 2a-e form charge-transfer (CT) complexes with chloranil (CHL), fluoranil (TFQ) and 2,3-dicyano-1,4-naphthoquinone (DCNQ). The donors 2a-d react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to yield 3-amino-5-arylthiadiazoles ? and DDQ-H2 (8). The thiosemicarbazide itself interacts with CHL via CT complexation to form the products 10-13. Heating of thiosemicarbazide (1) with 2,3-dichloro-1,4-naphthoquinone (DCHNQ) affords the {hiadiazine derivative 15. Recently, we have reported that the basicity of the system 2a-e stems from the conjugation between the aryl group and the x as well as n electrons and that the thiosemicarbazone system can undergo three different types of transitions based on the presence of the three donating centers X-K* (aryl group) n-x* (N atom) and n-x* (S atom)[2'].In this paper we present the results of our spectral investigation of the formation of C T complexes between the thiosemicarbazones 2a-e and several benzo-and naphthoquinones (Scheme l ) as well as of the irreversible chemical reactions observed for some donor-acceptor pairs.As shown in Table 1, the UVNIS absorption maxima obtained by mixing both donors 2a-e and the different x acceptor components in ethyl acetate as a solvent fall in the visible region. These maxima are attributed to C T complex formation, since both donor and acceptor alone d o not absorb in this region.The addition of donors 2a-e to both CHL and T F Q affords an initial C T complex, the absorbance of which does not change under the experimental conditions required for the determination of the association constants. However, on addition of 2a-e to DCNQ the initial formation of C T complexes is followed by a very slow chemical

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