Donor-acceptor-substituted diphenyl

Photochemical nucleophilic-substimtion reactions of cyanobenzene with allenes take place in a radical coupling process at the less heavily substituted radical site by donor-acceptor property. For example, 1,2,4,5-tetracyanobenzene 67 reacts with 1,1-dimethyIallene 68 in the presence of diphenyl to give 69 as major product [60]. 

Diphenyl porphyrins and their Zn° complexes substituted in the meso position by a Jt-delocalized substituent carrying an electron-donor or an electron-withdrawing group (49) were also investigated by the EFISH technique [169]. These second-order NLO chromophores have confirmed the ambivalent role of the polarizable porphyrin ring, which, in the ground state, already acts as a donor or acceptor. 

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