TY - JOUR

T1 - Structure and electronic properties of quinizarin chemisorbed on alumina

AU - Frank, Irmgard

AU - Marx, Dominik

AU - Parrinello, Michele

PY - 1996/5/22

Y1 - 1996/5/22

N2 - The anthraquinone dye molecule quinizarin is known to allow for persistent spectral hole burning up to liquid nitrogen temperatures after chemisorption on alumina surfaces. The mechanism underlying these improved hole-burning properties is not known, though is has been speculated that it might be related to intrinsic surface effects on the electronic structure of the dye. We approach this problem theoretically using gradient corrected density functional theory. The chemisorbed compound system is modelled by a periodically replicated nine layer slab which represents the (0001) surface of α-Al2O3. The chemisorption geometry obtained by geometry optimization and confirmed by Car-Parrinello molecular dynamics runs at room temperature is shown to be a perpendicular arrangement of quinizarin on the surface, where a chelate-like bond is formed with one exposed surface aluminum atom. In order to get information about the electronic structure, the frontier orbitals that are relevant for the description of the electronic excitation to the first excited state are evaluated for the isolated molecule, the chemisorbed molecule, and a quinizarin-aluminum-water complex. The strong red shift of the absorption frequency found in experiment upon chemisorption is reproduced. However, the results show that the shape of the frontier orbitals and hence the properties of the electronic excitation remain essentially unchanged by chemisorption. Thus, the differences in the behavior of the isolated and the chemisorbed dye observed in persistent spectral hole-burning experiments cannot be explained by genuine surface induced effects on the molecular electronic structure.

AB - The anthraquinone dye molecule quinizarin is known to allow for persistent spectral hole burning up to liquid nitrogen temperatures after chemisorption on alumina surfaces. The mechanism underlying these improved hole-burning properties is not known, though is has been speculated that it might be related to intrinsic surface effects on the electronic structure of the dye. We approach this problem theoretically using gradient corrected density functional theory. The chemisorbed compound system is modelled by a periodically replicated nine layer slab which represents the (0001) surface of α-Al2O3. The chemisorption geometry obtained by geometry optimization and confirmed by Car-Parrinello molecular dynamics runs at room temperature is shown to be a perpendicular arrangement of quinizarin on the surface, where a chelate-like bond is formed with one exposed surface aluminum atom. In order to get information about the electronic structure, the frontier orbitals that are relevant for the description of the electronic excitation to the first excited state are evaluated for the isolated molecule, the chemisorbed molecule, and a quinizarin-aluminum-water complex. The strong red shift of the absorption frequency found in experiment upon chemisorption is reproduced. However, the results show that the shape of the frontier orbitals and hence the properties of the electronic excitation remain essentially unchanged by chemisorption. Thus, the differences in the behavior of the isolated and the chemisorbed dye observed in persistent spectral hole-burning experiments cannot be explained by genuine surface induced effects on the molecular electronic structure.

UR - http://www.scopus.com/inward/record.url?scp=0000543828&partnerID=8YFLogxK

U2 - 10.1063/1.471490

DO - 10.1063/1.471490

M3 - Article

AN - SCOPUS:0000543828

VL - 104

SP - 8143

EP - 8150

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 20

ER -