EFFECT OF SOLVENT ON THE PHOTOCONTROLLED COORDINATION OF AZA ANALOGS OF 1-(9-ANTHRYL)-2-PHENYLETHENE TO A ZINC PORPHYRIN

The axial coordination of aza analogues of 1-(9-anthryl)-2-phenylethen e to zinc 5,10,15,20-tetratolylporphyrin (ZnTTP) was investigated. E-1 -(9-Anthryl)-2-(n-pyridyl)ethenes (n = 2, 3 and 4) (E-n-APyE), the Z i somers (n = 2 and 4) (Z-n-APyE) and E-1-(9-anthryl)-2-(2-pyrazinyl) et hene (E-APzE) were tested as aza analogues of 1-(9-anthryl)-2-phenylet hene. E-2-APyE, Z-2-APyE and E-APzE did not form a complex with ZnTTP. ZnTTP formed a complex with E-3-APyE, but complexation of ZnTTP with Z-3-APyE could not be observed because Z-3-APyE was not available. E-4 -APyE and Z-4-APyE showed a considerable difference in their ability t o form a complex with ZnTTP. In order to examine the effect of the sol vent polarity, the results in dichloromethane were compared with those in toluene. The extent of coordination of E-4-APyE to ZnTTP in dichlo romethane was significantly reduced due to the E --> Z photoisomerizat ion of E-4-APyE on UV irradiation. However, because the photoisomeriza tion of E-4-APyE was very inefficient in toluene, the extent of coordi nation of E-4-APyE to ZnTTP in toluene remained unchanged on UV irradi ation for up to 2 h. Therefore a change in solvent affected the photor esponsiveness of the system. (C) 1997 Elsevier Science S.A.