Synthesis and Ultrafast Excited-State Dynamics of Zinc and Palladium Triply Fused Diporphyrins

We report the synthesis and ultrafast excited-state dynamics of two new meso–meso, β–β, β–β triply fused diporphyrins, <b>Zn-3DP</b> and <b>Pd-3DP</b>. Both compounds were found to have short excited-state lifetimes: <b>Zn-3DP</b> possessed an average S₁ lifetime of 14 ps before nonradiative deactivation to the ground state, whereas <b>Pd-3DP</b> displayed a longer average S₁ lifetime of 18 ps before crossing to the T₁ state, which itself possessed a very short triplet lifetime of 1.7 ns. The excited-state dynamics of <b>Zn-3DP</b>, compared to similar zinc­(II) diporphyrins reported in the literature, suggests that a conical intersection of the S₁ and S₀ potential energy surfaces plays a major role as a deactivation pathway of these molecules. Furthermore, the short triplet lifetime of <b>Pd-3DP</b>, compared to other diporphyrins that also exploit the intramolecular heavy atom effect, reveals that the position of the heavy atom within the diporphyrin framework influences the strength of spin–orbit coupling. The implications for employing triply fused diporphyrins as NIR-absorbing triplet sensitizers are discussed

Kinetic Analysis of Photochemical Upconversion by Triplet−Triplet Annihilation: Beyond Any Spin Statistical Limit

Upconversion (UC) via triplet−triplet annihilation (TTA) is a promising concept to improve the energy conversion efficiency of solar cells by harvesting photons below the energy threshold. Here, we present a kinetic study of the delayed fluorescence induced by TTA to explore the maximum efficiency of this process. In our model system we find that more than 60% of the triplet molecules that decay by TTA produce emitters in their first excited singlet state, so that the observed TTA effiency exceeds 40% at the point of the highest triplet emitter concentration. This result thoroughly disproves any spin-statistical limitation for the annihilation efficiency and thus has crucial consequences for the applicability of an upconvertor based on TTA, which are discussed

Dye-Sensitized Solar Cell with Integrated Triplet–Triplet Annihilation Upconversion System

Photon upconversion (UC) by triplet–triplet annihilation (TTA-UC) is employed in order to enhance the response of solar cells to sub-bandgap light. Here, we present the first report of an integrated photovoltaic device, combining a dye-sensitized solar cell (DSC) and TTA-UC system. The integrated device displays enhanced current under sub-bandgap illumination, resulting in a figure of merit (FoM) under low concentration (3 suns), which is competitive with the best values recorded to date for nonintegrated systems. Thus, we demonstrate both the compatibility of DSC and TTA-UC and a viable method for device integration