Optical excitations in electroluminescent polymers: poly(para-phenylenevinylene) family

摘要

Component of photoexcited states with large spatial extent is investigatedfor optical absorption spectra of the electroluminescent conjugated polymers byusing the intermediate exciton theory. We calculate the ratio of oscillatorstrengths due to long-range excitons with respect to sum of all the oscillatorstrengths of the absorption as a function of the monomer number. The oscillatorstrengths of the long-range excitons in poly(para-phenylene) are smaller thanthose in poly(para-phenylenevinylene), and those ofpoly(para-phenylenedivinylene) are larger than those inpoly(para-phenylenevinylene) Such relative variations are explained by thedifferences of the number of vinylene units. The oscillator strengths oflong-range excitons in poly(di-para-phenylenevinylene) are much larger thanthose of the above three polymers, due to the increase of number of phenylrings. We also find that the energy position of the almost localized exciton isneary the same in the four polymers.