An investigation of the optical properties of tetraphenylporphyrin derivatives in Langmuir and Langmuir-Blodgett films

• Published in: Thin solid films 1994-05, Vol.243 (1), p.581-586
• Main Authors: Grieve, M.B., Hudson, A.J., Richardson, T., Johnstone, R.A.W., Sobral, A.J.F.N., Rocha Gonsalves, A.M.d'A.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; Polymers; organic compounds
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/0040-6090(93)04151-H

The optical properties of two tetraphenylporphyrin derivatives based on tetra(4-aminosulphonyl) phenylporphyrin have been examined. These porphyrins can exist in both free-base and dication states with their Soret absorption band occurring near 420 and 440 nm respectively. Floating monolayers can show the occurence of a new state characterized by two additional bands near 490 and 700 nm. The formation of this unknown state is dependent on both the subphase pH and the area occupied per monomer unit at the air-water interface. The effect of the subphase pH on the production of this state has been investigated systematically for both porphyrins and comparisons between the two habe been made. The optical absorption of Langmuir-Blodgett films for one of the porphyrins has also been examined. This has shown that the unknown state can be transferred on to glass substrates, though it is found not to be stable if stored in air.