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Titolo:
Ultrafast electron transfer dynamics from molecular adsorbates to semiconductor nanocrystalline thin films
Autore:
Asbury, JB; Hao, E; Wang, YQ; Ghosh, HN; Lian, TQ;
Indirizzi:
Emory Univ, Dept Chem, Atlanta, GA 30322 USA Emory Univ Atlanta GA USA 30322 ry Univ, Dept Chem, Atlanta, GA 30322 USA
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 20, volume: 105, anno: 2001,
pagine: 4545 - 4557
SICI:
1520-6106(20010524)105:20<4545:UETDFM>2.0.ZU;2-T
Fonte:
ISI
Lingua:
ENG
Soggetto:
TITANIUM-DIOXIDE FILMS; INTERFACIAL CHARGE-TRANSFER; ANATASE TIO2 FILM; RU-DYE MOLECULES; CDSE QUANTUM DOTS; LIQUID INTERFACES; INFRARED-SPECTROSCOPY; VIBRATIONAL DYNAMICS; SENSITIZING DYE; TRANSFER RATES;
Tipo documento:
Review
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
148
Recensione:
Indirizzi per estratti:
Indirizzo: Lian, TQ Emory Univ, Dept Chem, 1515 Pierce Dr, Atlanta, GA 30322 USA Emory Univ 1515 Pierce Dr Atlanta GA USA 30322 anta, GA 30322 USA
Citazione:
J.B. Asbury et al., "Ultrafast electron transfer dynamics from molecular adsorbates to semiconductor nanocrystalline thin films", J PHYS CH B, 105(20), 2001, pp. 4545-4557

Abstract

Interfacial electron transfer (ET) between semiconductor nanomaterials andmolecular adsorbates is an important fundamental process that is relevant to applications of these materials. Using femtosecond midinfrared spectroscopy, we have simultaneously measured the dynamics of injected electrons andadsorbates by directly monitoring the mid-IR absorption of electrons in the semiconductor and the change in adsorbate vibrational spectrum, respectively. We report on a series of studies designed to understand how the interfacial ET dynamics depends on the properties of the adsorbates, semiconductors, and their interaction. In Ru(dcbpy)(2)(SCN)(2) (dcbpy = 2, 2 ' -bipyridine-4,4 ' -dicarboxylate) sensitized TiO2 thin films, 400 nm excitation of the molecule promotes an electron to the metal-to-ligand charge transfer (MLCT) excited state, from which it is injected into TiO2. The injection process was characterized by a fast component, with a time constant of < 100 fs, and a slower component that is sensitive to sample condition. Similar ultrafast electron injection times were measured in TiO2 films sensitized by Ru(dcbpy)(2)(X)(2) (X-2 = 2CN(-) and dcbpy). Electron injection in these systems was found to compete with the vibrational energy relaxation process within the excited state of the molecules, leading to an injection yield thatdepends on the excited-state redox potential of the adsorbate. The injection rate from Ru(dcbpy)(2)(SCN)(2) to different semiconductors was found to obey the trend TiO2 > SnO2 > ZnO, indicating a strong dependence on the nature of the semiconductor. To understand these observations, various factors, such as electronic coupling, density pf states, and driving force, that control the interfacial ET rate were examined separately. The effect of electronic coupling on the ET rate was studied in TiO2 sensitized by three adsorbates, Re(L-n)(CO)(3)Cl [L-n is a modified dcbpy ligand with n (=0, 1, 3) CH2 units between the bipyridine and carboxylate groups]. We found that theET rate decreased with increasing number of CH2 units (or decreasing electronic coupling strength). The effect of driving force was investigated in Ru(dcbpy)(2)X-2 (X-2 = 2SCN(-), 2CN(-), and dcbpy) sensitized SnO2 thin films. In this case, we observed that the ET rate increased with the excited-state redox potential of the adsorbates, agreeing qualitatively with the theoretical prediction for a nonadiabatic interfacial ET process.

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Documento generato il 23/09/20 alle ore 06:20:42