Supramolecular zinc phthalocyanine-imidazolyl perylenediimide dyad and triad: synthesis, complexation, and photophysical studies

• Published in: Chemistry, an Asian journal Vol. 6; no. 11; p. 3110
• Main Authors: Céspedes-Guirao, F Javier, Ohkubo, Kei, Fukuzumi, Shunichi, Fernández-Lázaro, Fernando, Sastre-Santos, Angela
• Format: Journal Article
• Language: English
• Published: Germany 04.11.2011
• Subjects: Imides - analysis; Imides - chemistry; Indoles - analysis; Indoles - chemical synthesis; Indoles - chemistry; Ions - chemistry; Magnetic Resonance Imaging; Organometallic Compounds - analysis; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Perylene - analogs & derivatives; Perylene - analysis; Perylene - chemistry; Photoelectron Spectroscopy; Radiation-Sensitizing Agents - analysis; Radiation-Sensitizing Agents - chemical synthesis; Radiation-Sensitizing Agents - chemistry; Spectroscopy, Fourier Transform Infrared
• ISSN: 1861-471X
• DOI: 10.1002/asia.201100273

Two new supramolecular architectures based on zinc phthalocyanine (Pc) and imidazolyl-substituted perylenediimide (PDI), ZnPc/DImPDI/ZnPc 1 and ZnPc/ImPDI 2, have been prepared. A strong electron-donor, ZnPc-8, which contained eight tert-octylphenoxy groups was synthesized to ensure high solubility, thereby reducing aggregation in solution and providing σ-donor features while avoiding regioisomeric mixtures. Also, PDI units were functionalized with tert-octylphenoxy groups at the bay positions, which provide solubility to avoid aggregation in solution, together with one and two imidazole moieties in the amide position, PDI-6 and PDI-4, respectively, to be able to strongly coordinate with the ZnPc complex. Supramolecular complexation studies by (1)H NMR spectroscopy and ESI-MS demonstrate a high coordinative binding constant between imidazole-substituted PDI-4 or PDI-6 and ZnPc-8. The same results were confirmed by UV/Vis and fluorescence titration studies. UV/Vis titration studies revealed the formation of a 1:1 complex ZnPc/ImPDI 2 for the systems ZnPc-8 and PDI-6 and a 2:1 complex ZnPc/DImPDI/ZnPc 1 for the interaction of ZnPc-8 and PDI-4. The binding constant in both cases was determined to be on the order of 10(5) M(-1). Femtosecond laser flash photolysis measurements provided a direct proof of the charge-separated state within both supramolecular assemblies by observing the transient absorption band at 820 nm due to the zinc phthalocyanine radical cation. The lifetimes of charge-separated states are (9.8±3) ns for triad 1 and (3±1) ns for dyad 2. As far as we know, this is the first time that a radical ion pair has been detected in a supramolecular assembled ZnPc-PDI system and has obtained the longest lifetime of a charge-separated state published for ZnPc-PDI assemblies.