UV‐Vis‐spektroskopische Eigenschaften 3,5‐disubstituierter 1,3,4‐Oxadiazolin‐2‐imine. I. Einfluß der Substituenten und des Lösungsmittels auf die Absorption

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Abstract
The U.V.‐vis‐spectroscopic Properties of 3,5‐disubstituted 1,3,4‐Oxadiazoline‐2‐imines. I. The Influence of the Substituents and the Solvent on the AbsorptionThe u.v.‐vis data of 38 derivatives of 3,5‐disubstituted 1,3,4‐oxadiazoline‐2‐imines, measured in 12 different solvents, are discussed. The long wave absorption bands have charge‐transfer character, the observed solvatochromic shifts correlate with the solvent parameter ET. The assumed intramolecular charge‐transfer upon excitation is polarized in the direction R1N3C5R2. Derivatives which are donor‐substituted in the 3‐position of the oxadiazolinimine cycle (R1) and acceptor‐substituted in the 5‐position (R2) show a typical push‐pull effect. In this case bathochromic and hyperchromic effects on the long‐wave absorption bands result. On the other hand, R1is a donor and R2is an acceptor substituent the excitation energy is increasing.

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