Anthradithiophene Derivatives Substituted at the 2,8‐Positions by Formyl and Triphenylamine Units: Synthesis, Optical, and Electrochemical Properties

Abstract

The synthesis and characterization of two new anthradithiophene (ADT) derivatives substituted by thiophenyl or 2‐octylthiophenyl units at the 5,11‐positions and donor (triphenylamine) or acceptor (aldehyde functions) moieties at the 2,8‐positions of their backbone are described. Optical measurements were performed to evaluate the effect of electron‐rich/‐poor substituents on their stability towards photo‐oxidation and were supported by quantum chemical calculations and cyclic voltammetry experiments.

Mono‐Aryl/Alkylthio‐Substituted (Hetero)acenes of Exceptional Thermal and Photochemical Stability by the Thio‐Friedel–Crafts/Bradsher Cyclization Reaction

“…The various reaction conditions used for the photostability tests and a large number of other variables make it difficult to compare the photostabilities of the acenes of this study with those previously reported in the literature. However, our results can be compared with the results obtained under similar photostability testing conditions (244 and 366 nm, CHCl 3 ) for anthracenedithiophenes having an extended anthracene core, for which half‐lives t 1/2 of only 25–58 s have been reported . The photostability of 9‐AcO‐10‐(4‐AcO‐C 6 H 4 )‐substituted anthracene has also been reported to be in the order of seconds at 254 nm in chloroform .…”

“…our investigations) . The oxidation process, as already mentioned, primarily leads to endoperoxides, which may reproduce the acenes upon thermolysis or photolysis . For some acenes, such as anthracene, photodimerization occurs in the presence of air, especially in dilute solutions, in competition with photooxidation leading to the corresponding endoperoxide.…”

“…Similar differences were observed for the half‐life of the most photostable RS‐acene 6 f at 365 nm (R=4‐MeO‐C 6 H 4 ), for which t 1/2 =812 min in air, which is 80–100 times longer than the half‐life of the unsubstituted anthracene ( t 1/2 =8–10 min) under air atmosphere in polar media. Further comparison of the photostability of the electron‐rich anthracene 6 f ( t 1/2 =812 min) with electron‐rich anthracenedithiophenes possessing an extended anthracene core ( t 1/2 =25–40 s) shows that 6 f is at least 1200–1900 times more stable at 365 nm. Finally, the 6‐RS‐pentacenes reported in the literature under mild photochemical conditions (air, ambient light) have t 1/2 =29 min for R=Ph and t 1/2 =43 min for R=Ac, the difference being a result of the lower HOMO and LUMO energies of the anthracene substituted by a stronger electron‐withdrawing group (SAc versus SPh).…”