TiO2(110) Charge Donation to an Extended π-Conjugated Molecule.
The surface reduction of rutile TiO2(110) generates a state in the band gap whose excess electrons are spread among multiple sites, making the surface conductive and reactive. The charge extraction, hence the surface catalytic properties, depends critically on the spatial extent of the charge redistribution, which has been hitherto probed by small molecules that recombine at oxygen vacancy (Ovac) sites. We demonstrate by valence band resonant photoemission (RESPES) a very general charge extraction mechanism from a reduced TiO2(110) surface to an extended electron-acceptor organic molecule. Perylene-tetra-carboxylic-diimide (PTCDI) is not trapped at Ovac sites and forms a closely packed, planar layer on TiO2(110). In this configuration, the perylene core spills out the substrate excess electrons, filling the lowest unoccupied molecular orbital (LUMO). The charge transfer from the reduced surface to an extended π-conjugated system demonstrates the universality of the injection/extraction mechanism, opening new perspectives for the coupling of reducible oxides to organic semiconductors and supported catalysts.
†CNR-IOM, Laboratorio TASC, Basovizza SS-14, Km 163.5, 34149 Trieste, Italy.|§Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy.
Valeria
V
Lanzilotto
†CNR-IOM, Laboratorio TASC, Basovizza SS-14, Km 163.5, 34149 Trieste, Italy.|∥Dipartimento di Fisica, Università degli Studi di Trieste, Via Valerio 2, 34012 Trieste, Italy.
Giacomo
G
Lovat
‡Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy.|¶ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, 20125 Milano, Italy.
Guido
G
Fratesi
†CNR-IOM, Laboratorio TASC, Basovizza SS-14, Km 163.5, 34149 Trieste, Italy.|#Education Faculty, University of Ljubljana, Kardeljeva ploščad 16, 1000 Ljubljana, Slovenia.
Gregor
G
Bavdek
¶ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, 20125 Milano, Italy.
Gian Paolo
GP
Brivio
†CNR-IOM, Laboratorio TASC, Basovizza SS-14, Km 163.5, 34149 Trieste, Italy.
Luca
L
Floreano
charge transfer; metal oxide; polyconjugated aromatic hydrocarbon; resonant photoemission; synchrotron spectroscopy