The electrochemical properties of dyes D1eD5 have been analysed by cyclic voltammetry in methylene chloride in the presence
of Bu4NPF6as supporting electrolyte.Table 1summarizes all the
electrochemical properties of thefive dyes. Substitution of the
phenyl ring with an aliphatic fragment in the hydrazone moiety
and addition of the methyl group to the triphenylamine donor unit
in D4 lowers theE(S/S) by 0.07 V. Removal of an alkyl group from
the triphenylamine fragment and its substitution with the phenyl
moiety in the hydrazone fragment in molecule D1 raisesE(S/Sþ)by
0.05 V compared with D5. Moreover, it can be concluded from the
electrochemical characteristics of the investigated sensitizers that
the attachment of the hydrazone moiety to the triphenylamine
donor as an auxiliary group decreases the reduction potential and
increases the oxidation potential as well. The corresponding excited
state oxidation potentials (E(Sþ/S*)) (ca. 1.1 V) of the dye molecules with respect to the titania conduction band edge0.5vs
normal hydrogen electrode (NHE)[47] provides the thermodynamic driving force for charge injection. The energy offset of the
E(Sþ/S) (ca. 1.00 V) relative to that of the spiro-MeOTAD (0.69 V,
measured using CV) presents enough driving force for the dye