The Effect of Electron-Donating Moiety Structure on the Electrochemical and Photophysical Properties of Dithiophene- and Naphtho[2,1-B:3,4-B']dithiophene-substituted 1,3,4-Oxadiazoles and 1,3,4-Thiadiazoles

3-Alkyl- and 3-aryl-substituted [2,2'-dithiophene]-5-carboxylate esters, as well as naphtho[2,1-b:3,4-b']dithiophene-2-carboxylates were used in the synthesis of 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives. The obtained compounds were characterized with regard to their electrochemical and photophysical properties. The replacement of alkyl side chains with aryl substituents led to a substantial decrease of luminescence quantum yield and narrowing the energy gap between HOMO and LUMO, as well as a bathochromic shift of the absorption and emission peaks in the absorption and luminescence spectra. Changing from 3-aryldithiophene- to naphtho[2,1-b:3,4-b']-dithiophene-substituted 1,3,4-oxadiazoles and 1,3,4-thiadiazoles led to a slight increase of quantum yields, while the positions of LUMO and HOMO changed insignificantly.