Journal of Photochemistry, 14 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (1980) 89 - 60 0 Eisevier Sequoia &A., Lamanne - Printed in Switzerland 89 THERMOCHROMISM ANDPHOTOCHROMISM OF ARYL-SUBSTITUTED ACYCLIC AZINES II: PHOTOKINETICS K. APPENROTH, M. REICHENBACHER and R. PARTZOLD Sektion Chemie der Friedrich-Schiller-UnivereittTt, Jena (G.D.R.} (Received December 12,1979; in revised zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK form March 11,198O) Acyclic axines with higher condensed aromatic and heterocyclic sub- stituents are photochromic and show both thermal isomerization and photo- chemical isomerization. From the point of view of formal kinetics the azines can be divided into four reaction types depending on the substituents R1. The correspondence of the expected formal kinetic behaviour of the azines with the experimental results is a direct proof of a photochemical E-Z isomerixation of these compounds. We investigated acyclic azines which fulfil all criteria of a complicated unitary photoreaction of the type zyxwvutsrqponmlkjihgfedc A + B as well as those azines showing a reversible consecutive photoreaction A =+B * C. All quantum yields were determined using formal kinetics. 1. Introduction The photochemical zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA E-Z isomerization of the C=N bond has been exten- sively studied with hydrazones, anils, oxime ethers, azomethine dyes and triaxines [ 1 - 71. However, little is known about the photochemistry of 2,3- diaxabutadienes (axines) (Fig. 1). With the exception of qualitative investigations of some aryl-substituted azines as mixtures of E and 2 isomers on polychromatic irradiation, there have essentially only been reports on the irreversiblephotolysis of alkyl- and aryl- substituted azines [8 - 131. Fig. 1. The general structure of the 2,8+Sazabutadienes (azines).