Radical anions of π-conjugated oligomers and polymers: Delocalization and self trapping

We have studied radical anions of oligomeric series of differently linked conjugated π-systems by visible absorption and EPR/ENDOR spectroscopy, supported by quantum chemical calculations. The results obtained show very different features depending on the topology and geometry of the π-skeleton, the specific chain ends, and the counter ion effects. Upon chain length extension both spectroscopic methods yield complementary data allowing for a much deeper insight into characteristic molecular properties as limit of conjugation and structural reorganization upon charging. Three major topics for influencing the conjugation are summarized i) a comparison between linear and ladder type π-systems, ii) the topological control of conjugation as in para-, meta-, and ortho- phenylenevinylenes, and iii) the geometric hindrance in bi- and oligoarylenes.