Synthesis, Optical Properties, and Electronic Structures of Nucleobase-Containing π-Conjugated Oligomers

The molecular recognition properties of the nucleobases instruct the formation of complex three-dimensional architectures in natural and synthetic systems; relatively unexplored is their use as building blocks for pi-conjugated materials where they might mutually tune electronic and supramolecular structures. Toward this goal, an introductory set (1a-d and 2a-d) of six purine-terminated and two pyrimidine-terminated p-conjugated oligomers has been synthesized and used to develop experimental electronic and photophysical structureproperty trends. Unlike 2,2':5',2?-terthiophene (TTT) derivatives 2a-d, intramolecular charge transfer dominates oligomers 1a-d bearing a 4,7-bisthienylbenzothiadiazole (TBT) spacer due to the strong electron-accepting ability of its benzothiadiazole (BTD) ring. The resulting donoracceptordonor systems feature lower HOMOLUMO gaps than the terthiophene-linked nucleobases (Delta E-g similar to 1.8 eV vs 2.4 eV based on electrochemical measurements), and the lowest so far for p-conjugated molecules that include nucleobases within the p-framework. Experiments reveal a dependence of photophysical and electronic structure on the nature of the nucleobase and are in good agreement with theoretical calculations performed at the B3LYP/6-31+G** level. Overall, the results show how nucleobase heterocycles can be installed within p-systems to tune optical and electronic properties. Future work will evaluate the consequences of these information-rich components on supramolecular p-conjugated structure.