Stilbenoid Dimers: Dissection of a Paracyclophane Chromophore

A series of paracyclophane derivatives that hold chromophores of varying conjugation lengths has been synthesized using palladium-mediated coupling reactions. These molecules mimic solid-state interactions in main-chain polychromophores and conjugated emissive polymers such as poly(p-phenylenevinylene) (PPV). Their optical properties give insight into the energetics of photoexcitations localized in a discrete chromophore relative to a state containing the through-space delocalized paracyclophane core. Thus, 4-vinyl[2.2]paracyclophane (5) is obtained by reaction of 4-bromo[2.2]paracyclophane (3) and ethylene using Pd(OAc)2 and P(o-tol)3. Similar reactions starting with pseudo-o- or pseudo-p-dibromo[2.2]paracyclophane (4a and 4b, respectively) give the pseudo-o- and pseudo-p-divinyl products (6a and 6b, respectively). Using styrene instead of ethylene provides the styryl-substituted products. Thus, 4-styryl[2.2]paracyclophane (7) is obtained from 3 while pseudo-p- and pseudo-o-distyryl[2.2]paracyclophane (1...