π-Conjugation of two nitronyl nitroxides-attached diarylethenes.

Unusual blue shift of the absorption maxima of two nitronyl nitroxide attached diarylethene through phenyl units (DAE-phe-NN) with increasing number of phenyl units is examined by time dependent density functional theory (TDDFT). The extended π-conjugation between nitronyl nitroxide and diarylethene is rather suppressed by the bridge phenyl units. In comparison, the red shift found in two nitronyl nitroxide attached diarylethenes through thiophene units (DAE-thio-NN) with increasing number of thiophene units is due to the longer π-conjugation induced by smaller dihedral angles between diarylethene and bridge and between bridges.