Generally,
arylamine-based moieties, which have also been widely used
in materials of organic light-emitting diodes (OLEDs), are
employed as the electron donor due to the strong electrondonating
nature.6 On the other hand, carboxylic acid, cyanoacrylic
acid, or rhodanine-3-acetic acid were introduced into
the (D-π-A) system as the electron acceptor as well as the
anchoring group to the TiO2 surface.