Molecular Excitons and Plasmons in Acenes and Their Radical Cations

For existing and potential applications of acenes and acene derivatives, properties of their excited states play a central role. In describing these, the molecular orbital picture can reach its limits, and consideration within the quasi-particle picture can enable further insight. In this work, exciton size ( $d_{exc}$ ), hole and electron size ( ${\sigma }_h$ and ${\sigma }_e$ ) and correlation coefficient ( $R_{eh}$ ) of excited states of acenes and acene cations are investigated using TD-DFT at the TDA/CAM-B3LYP/6-311G* level, with a focus on their development with increasing acene length. Furthermore, employing a previously established approach, it is shown that the electronic structure of the ¹B_b and ²B_b states of neutral and cationic anthracene can be understood as molecular plasmons.