The dynamics of the
photoexcited states in the quaterthiophene-terminated
alkanethiolate self-assembled monolayer (SAM) on Au(111) are investigated
using time-resolved two-photon photoemission (2PPE) spectroscopy.
For SAMs with various alkylene (−(CH2)
n
−) chain lengths, a common stand-up configuration
of the quaterthiophene (4T) group is confirmed by infrared reflection
absorption spectroscopy (IRAS); the −(CH2)
n
– length controls the distance between 4T
and Au. Although the binding energies of the occupied and unoccupied
electronic levels of the 4T moiety are similar for all SAMs, the decay
dynamics of the photoexcited electrons at 4T strongly depends on the
−(CH2)
n
– length;
the lifetime changes from 0.2 to 3.9 ps by changing n from 3 to 13. The n dependent decay is explained
by the excitation transfer from 4T to the Au substrate.
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