Photochemical Charge Separation in Supramolecular Phthalocyanine−Multifullerene Conjugates Assembled by Crown Ether-Alkyl Ammonium Cation Interactions

Abstract

Self-assembled phthalocyanine-multifullerene donor-acceptor conjugates have been formed by crown ether-ammonium cation dipole-ion binding strategy to probe the photochemical charge separation. To achieve this, phthalocyanine is functionalized to possess four 18-crown-6 moieties on the macrocycle periphery, whereas fullerene is functionalized to possess an alkyl ammonium cation of short and long chain lengths. Stable donor-acceptor conjugates accommodating multifullerene entities have been obtained by the crown ether-ammonium cation inclusion complexation. From the efficient fluorescence quenching of the zinc phthalocyanine by the bound fullerene entities, the rate constants of charge separation are evaluated to be slightly larger for closely held via shorter alkyl chain length fullerene, which are also larger compared to the earlier reported analogous zinc porphyrin-multifullerene conjugate. Nanosecond transient absorption studies yielded spectral signatures corresponding to both the phthalocyanine radical cation and fullerene radical anion at the same time, providing evidence of light-induced electron transfer within the conjugates. The evaluated lifetimes of the radical ion pairs in the present phthalocyanine-fullerene conjugates are found to be hundreds of nanoseconds and are much longer compared to the earlier reported conjugate of zinc porphyrin analogue, revealing higher possible usage of the generated radical ion pairs.

Supramolecular electron transfer-based switching involving pyrrolic macrocycles. A new approach to sensor development?

“…In contrast, the unsubstituted cerium sandwich complex, CePc 2 , which is known to contain a tetravalent (Ce 4+ ) cation, displays no appreciable absorption intensity in the 500 nm spectral region. 34,36 On the basis of this comparison, as well as other considerations, the authors concluded that in solution the Ce 4+ oxidation state dominates for the Ce(15c5Pc) 2 complex, but upon the formation of monolayers, IET leads to the Ce 3+ oxidation state predominating.…”

Photosensitizing Electron Transfer Processes of Fullerenes, Carbon Nanotubes, and Carbon Nanohorns

“…An example is shown for ZnPc with multiple crown ethers, such as (crown) 4 ZnPc. Thus, the C 60 spheres with inclusion of −NH 3 + cannot approach the ZnPc‐surface (Figure a), which contrasts with (crown)ZnP approaching the C 60 sphere (Figure a, right). In the ns‐transient absorption spectra (Figure b), the lower intensity of the 700 nm band of 3 C 60 * supports the higher yield of complex formation, since the absorption intensity at 700 nm is a measure of uncomplexed C 60 .…”

Conjugated compounds in supramolecular informational systems: A review

“…Since then, molecular systems that exhibit bista bility-the ability to exist in two different electronic states and change their electronic state upon the effect of external actions-have attracted especial attention of researchers. The continuing interest in processes of reversible intramolecular electron transfer exists because these processes appear promising as a basis for develop ment of molecular sensors and nanosized devices for recording and storage of information [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42].…”

“…Presently, such effects as changes in the microenvi ronment (solvent replacement) [23,24,31,43] and thermal [27,28,33,[43][44][45] and magnetic and photo physical [26,30,32,38,39,[46][47][48] effects are used most widely as external controlling signals. Some separate works that describe the processes of redox isomerization in a 3D system under the influ ence of external pressure [49,50] deserve special atten tion.…”