1 research outputs found
Ultrafast Interfacial Charge-Transfer Dynamics in a Donor-Ï€-Acceptor Chromophore Sensitized TiO<sub>2</sub> Nanocomposite
The dynamics of interfacial charge
transfer across (<i>E</i>)-3-(5-((4-(9H-carbazol-9-yl)Âphenyl)Âethynyl)Âthiophen-2-yl)-2-cyanoacrylic
acid (CT-CA) and TiO<sub>2</sub> nanocomposites was studied with femtosecond
transient absorption, fluorescence upconversion, and molecular quantum
dynamics simulations. The investigated dye, CT-CA is a push–pull
chromophore that has an intramolecular charge-transfer (ICT) excited
state and binds strongly with the surface of TiO<sub>2</sub> nanoparticles.
Ultrafast transient absorption and fluorescence measurements, in both
solution and thin film samples, were carried out to probe the dynamics
of electron injection and charge recombination. Multiexponential electron
injection with time constants of <150 fs, 850 fs, and 8.5 ps were
observed from femtosecond fluorescence measurements in solution and
on thin films. Femtosecond transient absorption measurements show
similar multiexponential electron injection and confirm that the picosecond
electron injection component arises from the excited ICT state of
the CT-CA/TiO<sub>2</sub> complex. Quantum dynamics calculations also
show the presence of a slow component (30%) in the electron injection
dynamics although most of the electron injection (70%) takes place
in less than 20 fs. The slow component of electron injection, from
the local ICT state, is attributed to the energetic position of the
excited state, which is close to, or slightly below, the conduction
band edge. In addition, the transient bleach of CT-CA on the TiO<sub>2</sub> surface is shifted to longer wavelengths when compared to
its absorption spectrum and the transient bleach is further shifted
to longer wavelengths with charge recombination. These features are
attributed to transient Stark shifts that arise from the local electric
fields generated at the dye/TiO<sub>2</sub> interface due to charge-transfer
interactions