Synthesis of Thieno-Bridged Porphyrins: Changing the Antiaromatic Contribution by the Direction of the Thiophene Ring

Two types of thieno-bridged porphyrins were synthesized
by incorporating
a thiophene group across their meso and β positions with different
directions of the thiophene ring to investigate the aromaticity of
these porphyrins with extended π-systems. The 2,3-thieno-bridged
porphyrin showed a larger antiaromatic contribution than did the 3,4-thieno-bridged
porphyrin. In the former, the antiaromatic contribution is based on
a 20-π-electron conjugated circuit. The two thieno-bridged porphyrins
were characterized by calculations of nucleus-independent chemical
shift and anisotropy of the induced current density as well as by
X-ray crystallography, NMR spectroscopy, UV–vis–NIR
absorption spectroscopy, electrochemical studies, time-resolved excited-state
analysis, and two-photon absorption cross section measurements. Chemical
derivatization of the 2,3-thieno-bridged porphyrin was also demonstrated.