Willig, F.; Ernstorfer, R.; Gundlach, L.; Felber, S.; Zimmermann, C.; Eichberger, R.; Storck, W.; Töben, L.; Galoppini, E.; Wei, Q.: Heterogeneous electron transfer in ultra-high vacuum probed with femtosecond transient absorption and two-photon-photoemission. In: Trombay Symposium on Radiation and Photochemistry TSRP-2004, January 8-12, 2004, BARC, Mumbai / Volume 1Mumbai: BARC, 2004, p. 110-114
Abstract:
Electron injection from the excited singlet state of the molecular chromophore perylene to the wide band gap semiconductor TiO2 was investigated in ultra-high-vacuum with femtosecond transient absorption (fs-TA) on nano-structured anatase TiO2 and with fs two-photon photoemission (fs-2PPE) on rutile TiO2(110) single crystals. The data for different saturated anchor-cum-spacer groups revealed an exponential distance dependence of electron transfer with a decay parameter of 0.1nm, where the shortest injection time was 13 fs for the carboxyl anchor group. With a long rigid spacer-cum-anchor group (TriPod) attached to perylene the distance of about 1 nm was achieved between the rim of the chromophore and the surface atoms. Correspondingly slow electron transfer was measured for this compound with a time constant of 4 ps via fs-2PPE on the surface of the rutile single crystal. The latter value was in fair agreement with the longest time constant of 4ps measured also with the TriPod spacer but on nano-structured anatase TiO2 via fs-TA. In the latter system different adsorption sites gave rise to different reaction distances. From the UPS and fs-2PPE data it was deduced that electrons were injected predominantly into electronic levels about 0.8 eV above the lower edge of the conduction band of TiO2.