Highly photoactive chemically modified thin films of chloroaluminum (and bromoaluminum) phthalocyanines probed by NEXAFS and UPS: determination of the electronic structure and the molecular orientation

• Published in: Journal of physical chemistry (1952) 1991, Vol.95 (1), p.251-257
• Main Authors: Guay, D, Tourillon, G, Gastonguay, L, Dodelet, J. P, Nebesny, K. W, Armstrong, N. R, Garrett, R
• Format: Article
• Language: English
• Subjects: 140505 - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); 400500 - Photochemistry; ABSORPTION SPECTROSCOPY; ALUMINIUM; BROMINE; CHEMISTRY; CHLORINE; DATA; DYES; ELECTRON SPECTROSCOPY; ELECTRONIC STRUCTURE; ELEMENTS; Exact sciences and technology; EXPERIMENTAL DATA; General and physical chemistry; HALOGENS; HETEROCYCLIC COMPOUNDS; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MEASURING METHODS; METALS; MOLECULAR STRUCTURE; NONMETALS; NUMERICAL DATA; ORGANIC COMPOUNDS; PHOTOCHEMISTRY; PHOTOELECTRON SPECTROSCOPY; PHTHALOCYANINES; SOLAR ENERGY; Solid-liquid interface; SPECTROSCOPY; Surface physical chemistry; THIN FILMS
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100154a049

Near edge x-ray absorption fine structure (NEXAFS) at the C and N K edges and UV photoelectron spectroscopy (UPS) at variable excitation energy (21.2 and 120 eV) have been used to characterize the electronic structure and the molecular orientation of chloroaluminum phthalocyanine (ClAlPc) thin films deposited on glass or SnO{sub 2} substrates and subjected to chemical transformations. Transformation H occurs when the films are soaked in an aqueous acidic solution, while transformation I is observed if I{sub 3}{sup {minus}}/I{sup {minus}} is added to the solution. It is demonstrated that the protonation of the aza nitrogen atoms of ClAlPc happens during both transformations. It modifies the valence band of the compound but has no effect on the unoccupied levels of the material. Besides the protonation, the uptake of I{sub 3}{sup {minus}} in the phthalocyanine film during transformation I leads to the formation of a charge-transfer complex between the phthalocyanine and the iodine species with a modification of both the occupied and unoccupied levels of the material. The band gap is reduced by 0.3 eV and 1.5 eV for transformations H and I, respectively. No orientation-dependent effect is observed when the chloroaluminum phthalocyanine is deposited on SnO{sub 2}. On the contrary, strong polarization effects are observed in the NEXAFS spectra of phthalocyanine deposited on a float glass substrate.