Photoinduced electron transfer has been observed in a molecular triad, consisting of a porphyrin (P) covalently linked to a tetrathiafulvalene (TTF) and a fullerene derivative (C 60), in the different phases of the liquid crystal E-7 and in a glass of 2-methyltetrahydrofuran (2-MeTHF) by means of time-resolved electron paramagnetic resonance (EPR) spectroscopy. In both solvents, an EPR. signal observed immediately after excitation has been assigned to the radical pair TTF .+P-C 60 .-, based on its magnetic interaction parameters and spin polarization pattern. In the 2-MeTHF glass and the crystalline phase of E-7, the TTF .+-P-C 60 .- state is formed from the TTF- 1P-C 60 singlet state via an initial TTF-P .-C 60 .- charge-separated state. Long-lived charge separation (∼8 μs) for the singlet-born radical pair is observed in the 2-MeTHF glass at cryogenic temperatures. In the nematic phase of E-7, a high degree of ordering in the liquid crystal is achieved by the molecular triad. In this phase, both singlet- and triplet-initiated electron transfer routes are concurrently active. At room temperature in the presence of the external magnetic field, the triplet-born radical pair T(TTF .+-P-C 60 .-) has a lifetime of ∼7 μs, while that of the singlet-born radical pair s(TTF .+-P-C 60 .-) is much shorter (<1μs). The difference in lifetimes is ascribed to spin dynamic effects in the magnetic field.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry