CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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energy change is the only factor determining BET rate. This can be explained only on the
basis of size quantization. In a size quantized system not only the conduction levels become
discrete, the conduction band also moves upward which effectively increases the free energy
(-G 0 ) of charge recombination reaction. Again due to the discrete nature of the different
energy levels of the conduction band the carrier relaxation dynamics of injected electron will
be much slower as compared to the bulk system. As a result the energy level of the injected
electron lies at much higher level as compared to the bulk one. So for a given injected
electron and parent cation pair free energy of charge recombination reaction will be much
higher as compared to the bulk system. Higher free energy of charge recombination falls in
the Marcus inversion regime, which reduces rate the BET of reaction. These observations
further accentuate the evidence of the injection dynamics result which essentially concluded
that the injection dynamics could only be accounted on the basis of the finite size effects.
3. 4. Conclusions
In conclusion, ultrafast transient absorption studies have been carried out to throw
light on the interfacial electron transfer dynamics in alizarin/TiO 2 system. Optical absorption
spectra showed the appearance of shoulder on the red side of the main alizarin absorption
indicating a charge transferred state. The electron transfer dynamics was compared with
alizarin/bulk TiO 2 surface modified particle. The injection dynamics revealed multiexponential
injection indicating injection into different discrete levels in CB. The multiexponential
injection indicates a nonadiabatic injection unlike the conclusion of the previous
study. The aggregation and the multilayer formation as the cause of the multi-exponential
injection has been ruled out due to dilute solution of alizarin that has been used in the present