The Influence of Terminal Push–Pull Substitution on the Electronic Structure and Optical Properties of Pentacenes

The synthesis of 2,3‐R 2 ‐9,10‐(OMe) 2 ‐substituted pentacenes (R=OMe, F, Br, CN; 1 – 4 ) from 2,3‐R 2 ‐9,10‐dimethoxy‐6,13‐dihydro‐6,13‐ethanopentacene‐15,16‐diones (α‐diketone‐bridged precursors) by photochemically induced bis‐decarbonylation (Strating–Zwanenburg reaction) is described. Under matrix‐isolation conditions (solid Ar, 10 K) the S 1 transitions of 1 and 2 undergo hypsochromic and those of 3 and 4 bathochromic shifts compared to parent pentacene. The S 1 transition wavelengths correlate well with the difference of substituent parameters σ p . A computational analysis of the excited states at the CAM‐B3LYP/6‐311+G** level of theory provides an assignment of the electronic transitions. Photolysis in solution at room temperature yields red [R=OMe ( 1 )], blue [R=Br ( 3 ), F ( 2 )], and green [R=CN ( 4 )] pentacenes. The compounds are oxygen‐sensitive and have low solubility, but their formation can be monitored by UV/Vis and, in the case of R=CN, also by 1 H NMR spectroscopy. The S 1 transition in 4 does not show the typical pentacene fine structure in the electronic absorption spectrum. Photogeneration in the presence of oxygen leads to a number of photoproducts that could be identified by monitoring the reaction by 1 H NMR spectroscopy for R=OMe.