Side-Chain-Controlled Aggregation of Amphiphilic Porphyrins in Thin Langmuir-Blodgett Films

This paper is dedicated to Professor Tohru Takenaka on the occasion of his retirement. Aggregation behaviors of amphiphilic porphyrins with one (THPPH1) , two (cis-THPPH2 and trans-THPPH2) , three (THPPH3) and four (THPPH4) hexadecyloxyphenyl chains have been investigated in Langmuir-Blodgett (LB) films by means of UV-vis absorption spectroscopy and Cu (II) metallation. For the LB films of THPPH1, cis- and trans-THPPH2, the Soret absorptions are red-shifted (434nm) re-lative to the solution value (420nm),where as the Q-state absorptions are essentially unaltered. For the films of THPPH3 and THPPH4, the Soret bands are split into two components; one is red-shifted (440nm) and the other blue-shifted (398nm) with respect to the dilute solution value. The spectral data are inter-preted in terms of exciton interactions between the porphyrin Soret excited states and are used to deduce the molecular arrangement of the porphyrin macrocycles in the films. When transferred from the mono-layers on aqueous Cu (II) subphase, the LB films of THPPH1, cis-THPPH2, trans-THPPH2 and THPPH3 give the Q-state bands at 552 and 518 nm, being characteristic of copper-porphyrin complex, and the film of THPPH4 gives the Q-state absorption bands identical with those of its free base form. Time de-pendence of Cu (II) metallation of the LB films of these amphiphilic porphyrins demonstrate the metalla