Modulation of Energy Transfer into Sequential Electron Transfer upon Axial Coordination of Tetrathiafulvalene in an Aluminum(III) Porphyrin–Free-Base Porphyrin Dyad

Abstract

Axially assembled aluminum(III) porphyrin based dyads and triads have been constructed to investigate the factors that govern the energy and electron transfer processes in a perpendicular direction to the porphyrin plane. In the aluminum(III) porphyrin-free-base porphyrin (AlPor-Ph-H2Por) dyad, the AlPor occupies the basal plane, while the free-base porphyrin (H2Por) with electron withdrawing groups resides in the axial position through a benzoate spacer. The NMR, UV-visible absorption, and steady-state fluorescence studies confirm that the coordination of pyridine appended tetrathiafulvalene (TTF) derivative (TTF-py or TTF-Ph-py) to the dyad in noncoordinating solvents afford vertically arranged supramolecular self-assembled triads (TTF-py→AlPor-Ph-H2Por and TTF-Ph-py→AlPor-Ph-H2Por). Time-resolved studies revealed that the AlPor in dyad and triads undergoes photoinduced energy and/or electron transfer processes. Interestingly, the energy and electron donating/accepting nature of AlPor can be modulated by changing the solvent polarity or by stimulating a new competing process using a TTF molecule. In modest polar solvents (dichloromethane and o-dichlorobenzene), excitation of AlPor leads singlet-singlet energy transfer from the excited singlet state of AlPor ((1)AlPor*) to H2Por with a moderate rate constant (k(EnT)) of 1.78 × 10(8) s(-1). In contrast, excitation of AlPor in the triad results in ultrafast electron transfer from TTF to (1)AlPor* with a rate constant (k(ET)) of 8.33 × 10(9)-1.25 × 10(10) s(-1), which outcompetes the energy transfer from (1)AlPor* to H2Por and yields the primary radical pair TTF(+•)-AlPor(-•)-H2Por. A subsequent electron shift to H2Por generates a spatially well-separated TTF(+•)-AlPor-H2Por(-•) radical pair.

A Divalent Pentastable Redox‐Switchable Donor–Acceptor Rotaxane

“…[63] These values result in a D ET G8 value of (À61.5 AE 6.8) kJ mol À1 www.chemeurj.org (À0.64 eV) in dichloromethane, which is in the upper range for similar supramolecular D-A systems. [64][65][66][67] Therefore, the charge separation between the excited D*-A complex and D + -A À is thermodynamically highly favoured.…”

Design and photochemical study of supramolecular donor–acceptor systems assembled via metal–ligand axial coordination

“…On the other side of the Al porphyrin, a pyridine appended TTF derivative was axially coordinated to the central Al atom of AlPor to form a self-assembled donor-acceptor supramolecular triad complex (seeFig. 42for structure)[128].The free-base porphyrin with electron withdrawing fluorine atoms at meso positions was selected as an acceptor for both energy and electron transfer processes because of its spectral overlapping with AlPor and positive redox potentials suitable for an electron acceptor.At the same time tetrathiafulvalene (TTF) was selected as a secondary donor because of its strong electron donating ability. The absorption spectrum of the dyad Al(III)Por-H 2 P was recorded in DCM, which revealed three Q bands located at 510, 547, and 639 nm corresponding to H 2 Por (87%), AlPor (90%), and H 2 Por (60%), respectively.…”

Distance‐Dependent Electron Transfer Kinetics in Axially Connected Silicon Phthalocyanine‐Fullerene Conjugates

“…[25][26][27][28][29][30][31][32][33] In the context of donor-acceptor design, there are few examples of covalent multimodular artificial photosynthetic systems, where electron-acceptor units are arranged in the axial positions of a suitable porphyrinoid macrocycle, thus providing molecular systems that undergo photo-induced electron transfer processes in a very efficient way. [19,[34][35][36][37][38][39][40][41][42][43][44][45] One of the most versatile building-blocks is silicon phthalocyanine (SiPc), which can be easily functionalized at axial positions through a variety of functionalities. Our groups have experience in syntheses and photophysical study of SiPc-based donor-acceptor arrangements.…”