Theoretical analysis of third order polarizability enhancement of disubstituted diphenyl polyenes via oxidative doping

The static field third order polarizability, γ_xxxx(0;0,0,0), is calculated for an oligomeric series of disubstituted diphenyl polyenes and their bipolarons by using INDO‐PSDCI finite perturbation procedures. Our procedures have the advantage of maintaining a degree of size consistency that is difficult to achieve by using the sum‐over‐states approach. The chain length dependance of γ_xxxx(0;0,0,0) is calculated to be 21.6N^1.9×10⁻³⁶ esu and 20.1N^2.3×10⁻³⁶ esu for the neutral and bipolaronic species, respectively, where N is the number of carbon atoms in the polyene chain. Although our calculations agree with previous studies that predict that a bipolaron will have an enhanced third order polarizability relative to the corresponding neutral polyene, the length dependance that we observe for both the neutral and bipolaronic species is much smaller than that predicted by previous literature investigations.