Speaker
Description
We present recent results on the photophysics and optical properties of
nanographenes. The first part of the talk focuses on the photophysics of cove-edge hexa-peri-hexabenzo-bis-peri-octacenes. The remarkable light emission properties and lack of excited state absorption upon solvation give rise to net stimulated emission and amplified spontaneous emission, largely enabled by the cove-edge pattern. Therefore, this nanographene system stands as a promising optical gain medium in laser cavities.
In the second part of the talk, we will focus on a family of edge-fused nickel porphyrin-nanographenes. Porphyrins are appealing building blocks for solar energy applications, although their photosensitization capability is limited by their large optical energy gap, resulting in a mismatch in absorption for efficient harvesting of the solar spectrum. Porphyrin π-extension by edge-fusing with nanographenes can be employed to narrow their optical energy gap, enabling the development of porphyrin-based panchromatic dyes with an optimized energy onset for solar energy conversion in dye-sensitized solar fuel and solar cell configurations. Combined pump-probe measurements with time-dependent density functional theory demonstrate that photoexcitation in these nickel porphyrin-nanographenes leads to a lowest ligand-centered singlet state, which undergoes ultrafast intersystem crossing (1.2 ps) towards an intermediate (d,d) triplet level, unaffected by the symmetric conjugation expansion. Remarkably, this triplet level delocalizes into a ligand centered triplet state in 18 ps, an asset for sunlight-to-energy conversion. This observation implies that the decoration of the porphyrin moiety with nanographenes, while significantly impacting the absorption onset of the novel dye, promotes the formation of a ligand-centered lowest triplet state with a large spatial extension, potentially interesting for boosting interactions with electron scavengers.
[1] Gu, Yanwei, et al. "Cove‐Edged Hexa‐peri‐hexabenzo‐bis‐peri‐octacene:
Molecular Conformations and Amplified Spontaneous Emission." Angewandte
Chemie International Edition 61.18 (2022): e202201088.
[2] Garcia-Orrit, Saul, et al., "Nanographene-based decoration as a panchromatic antenna for metalloporphyrin conjugates", Small (2023) 2301596. https://doi.org/10.1002/smll.202301596.
