Novel azomethines consisting uniquely of thiophene units were examined. The highly conjugated compounds were prepared by condensing air stable aminothiophenes with 2-thiophene aldehydes, which were substituted with various electronic groups. The resulting azomethines are highly conjugated and are both reductively and hydrolytically resistant. Various electron donating and accepting groups placed in the 2-position of 5-thiophene carboxaldehyde lead to electronically delocalized push–push, pull–pull, and push–pullazomethines. These electronic groups affect both the HOMO and the LUMO levels, which influence the absorption and emission spectra. Colors spanning the entire visible spectrum ranging from yellow to blue are possible with these nitrogen containing conjugated compounds. Excited state deactivation of the singlet excited state occurs predominately by internal conversion while only a small amount of energy is dissipated by intersystem crossing to the triplet state and by fluorescence. The ensuing fluorescence and phosphorescence of the thiopheno azomethines are similar to those of their thiophene analogues currently used in functional devices, but with the advantage of a low triplet state and tunable HOMO–LUMO energy levels extending from 3.0 to 1.9 eV. Quasi-reversible electrochemical radical cation formation is possible while the oxidation potential is dependent on the nature of the electronic group appended to the thiophene. The crystallographic data of the electronic push–push system show the azomethine bonds are planar and linear and they adopt the E isomer.

A conjugated all-fluorene polyazomethine (6) was prepared from the condensation of 9,9′-dioctyl fluorene dialdehyde and 9,9′-dihexyl fluorene diamine. The resulting polymer was soluble in common organic solvents courtesy of the solubilizing alkyl groups in the 9,9′ positions. Determination of the polymer's molecular weight was subsequently possible using standard characterization methods. Polymer formation was confirmed both by GPC and NMR with average number molecular weights ranging from 9 to 145 kg mol⁻¹. The absolute fluorescence quantum yield (Φ_fl) of 6 in dichloromethane was 0.19 while in thin films the value increased to 0.40. The fluorescence could further be restored to unity at 77 K while Φ_fl = 0.76 was possible by protonating 6 with trifluoroacetic acid. 6 underwent stark color changes from yellow to red upon doping with TFA and FeCl₃ and the resulting intermediates could be neutralized with Et₃N and hydrazine hydrate, respectively. Reversible protonation/deprotonation was possible both in solution and thin films. Meanwhile, electrochemical oxidation of 6 at ca. 1.5 V resulted in a 120 nm bathochromic change in the absorbance. The intermediate could be reduced at −0.2 V to regenerate the neutral 6 that absorbed at 425 nm. The Job method confirmed that the oxidized intermediate was the radical cation.