Interpretation of the vibrational spectra of planarized poly-p-phenylene

We present an interpretation of the Raman and IR spectra of planarized poly(p-phenylene). The newly synthesized PPP, planarized with methylene bridging groups, is predicted to have a much higher inter-ring stretching frequency although the inter-ring bond length (1.475Å) is only slightly shorter than that of pristine PPP. This is supported by the Raman spectrum of a substituted planarized PPP. The IR spectrum of planarized PPP is predicted to have strong peaks in the 1350–1450 cm−1 region. The CH out-of-plane bending mode was found to be 840 cm−1 which is consistent with that of a 1,2,4,5,-tetrasubstituted phenyl ring.