FACILE SYNTHESIS AND NONLINEAR-OPTICAL PROPERTIES OF PUSH-PULL 5,15-DIPHENYLPORPHYRINS

A series of 5,15-diphenylporphyrinatonickel(II) derivatives containing electron-releasing (Me-2-NC6H4C=C-) and -withdrawing groups [-CHO, -C H=C(CN)(2), -CH=C(CO2Et)(2), -CH=CHCHO] in opposite meso positions has been synthesized through the classical formylation, halogenation, Kno evenagel condensation, and palladium-catalyzed cross-coupling reaction of porphyrins. The molecular first hyperpolarizabilities (beta) of tw o of these push-pull porphyrins, namely 5-(2',2'-dicyanoethenyl)- 15-[ [4 enyl]ethynyl]-10,20-diphenylporphyrinatonickel(II) (7) and )phenyl] ethynyl]-10,20-diphenylporphyrinatonickel- (II) (8) have been determin ed experimentally by electric-field-induced second-harmonic generation (EFISH) at 1907 nm and computationally by semiempirical methods (ZIND O sum-over-states). The values of beta(mu) (124 and 66 x 10(-30) cm(5) esu(-1), for 7 and 8, respectively) are moderate because the acceptor group is significantly tilted with respect to the porphyrin core in t hese complexes, which decreases the electronic coupling across the sys tem. This nonplanar geometry has been confirmed by X-ray structure ana lyses and molecular modeling studies.