Influence of interchain interactions on the electronic properties of neutral and charged oligodiacetylenes carrying bulk substituents.

We discuss the effect of the interchain interactions on the electronic properties of a "dimer", named (CHD(4))(2), built from two molecules of a fully carbazolyl-substituted oligodiacetylene containing four repeating units. Each carbazolyl moiety is connected to its respective backbone through a methylene spacer, and the excitations of the neutral and doubly positively charged dimer are obtained using the CIS (configuration interaction including singles) and CEO (collective electronic oscillator) models. The separation distance between the backbones is fixed to a value that could possibly imply a very weak, if any, interchain interaction between the oligomers. In the charged dimer, where we have not been able to perform CEO calculations, it can be expected from previous results that the CIS method will behave satisfactorily. Contrary to the neutral case and surprisingly enough, the simulated photoinduced absorption (PA) spectra indicate a substituent-induced strong interaction between the oligomers, due to the very large amount of excess charge on the distorted oligomer which is spread over its carbazolyl moieties. Broadening of the lowest energy band due to the latter interaction improves the agreement between the theoretical and the experimental PA spectrum for the corresponding polymer. The through-space charge transfer directly connecting the charged with the neutral molecule could supply an efficient channel for charge transport in substituted polydiacetylenes.