Triplet Photosensitizers Showing Strong Absorption of Visible Light and Long-Lived Triplet Excited States and Application in Photocatalysis: A Mini Review
About: This article is published in Energy & Fuels.The article was published on 2021-08-19. It has received 19 citations till now. The article focuses on the topics: Absorption (electromagnetic radiation).
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TL;DR: In this article, the discovery of photocatalysts that can convert CO2 into hydrocarbons is discussed. But, the authors do not consider the effects of CO2 emissions on the environment.
Abstract: Photoreduction of CO2 can effectively alleviate the troublesome global energy crisis and environmental problems by converting CO2 into hydrocarbons. Due to the discovery of photocatalysts that can ...
26 citations
TL;DR: In this paper , a system for visible light-driven hydrogen production from water is reported, which makes use of a synthetic mini-enzyme known as a mimochrome (CoMC6*a) consisting of a cobalt deuteroporphyrin and two attached peptides as a catalyst, [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) as a photosensitizer, and ascorbic acid as a sacrificial electron donor.
9 citations
TL;DR: In this article , two Pt(II)-porphyrins conjugated with naphthalimide (NI) chromophore, PtT(p-NI)PP and PtD(p)-NIPP, are synthesized in excellent yields and characterized by photophysical, electrochemical, and density functional theory studies.
Abstract: Two Pt(II)-porphyrins conjugated with naphthalimide (NI) chromophore, PtT(p-NI)PP and PtD(p-NI)PP, are synthesized in excellent yields and characterized by photophysical, electrochemical, and density functional theory studies. Both Pt(II)-porphyrins possess an efficient...
8 citations
TL;DR: In this article , the impact of molecular-twist on these energetics governing ISC is unveiled in a series of highly fluorescent prototype perylenediimides (PDIs) in dichloromethane implementing reliable quantum-chemical calculations.
Abstract: Singlet-triplet gap (ΔES - T) and spin-orbit coupling (SOC) primarily govern intersystem crossing (ISC)-mediated photo- and electro-luminescence processes. Structural-twist in organic molecules is known to improve ISC efficiency. However, how and to what extent a twist affects the ΔES - T and SOC are not yet fully understood. In this work, the impact of molecular-twist on these energetics governing ISC is unveiled in a series of highly fluorescent prototype perylenediimides (PDIs) in dichloromethane implementing reliable quantum-chemical calculations. While S1 → T1 ISC remains suppressed with increasing twist, a relatively larger decrease in ΔES - T together with a modest increase in SOC results in enhanced S1 →T2 ISC. Significantly modulated ISC rates are predicted in a few experimentally relevant -CN- and -Br-substituted PDIs, where twist of varied extent arises naturally depending on substituent's chemical nature, numbers, and positions. This study uncovers the critical role of molecular-twist in tailoring ISC and thereby helps designing functional organic triplet-generating materials.
7 citations
TL;DR: In this article , a few chalcogen (X = O, S, Se) bay-substituted PDIs (PDI-X2) are computationally modeled aiming at introducing geometrical-strain at the PDI core and also mixing nπ* orbital character to ππ* in the lowest singlet and triplet excited states, which altogether may reduce ΔES-T and also improve the SOC.
Abstract: Molecular-scale design strategies for promoting intersystem crossing (ISC) in small organic molecules are ubiquitous in developing efficient metal-free triplet photosensitizers with high triplet quantum yield (ΦT). Air-stable and highly fluorescent perylenediimide (PDI) in its pristine form displays very small ISC compared to the fluorescence due to the large singlet-triplet gap (ΔES-T) and negligibly small spin-orbit coupling (SOC) between the lowest singlet (S1) and triplet state (T1). However, its ΦT can be tuned by different chemical and mechanical means that are capable of either directly lowering the ΔES-T and increasing SOC or introducing intermediate low-lying triplet states (Tn, n = 2, 3, …) between S1 and T1. To this end, herein, a few chalcogen (X = O, S, Se) bay-substituted PDIs (PDI-X2) are computationally modeled aiming at introducing geometrical-strain at the PDI core and also mixing nπ* orbital character to ππ* in the lowest singlet and triplet excited states, which altogether may reduce ΔES-T and also improve the SOC. Our quantum-chemical calculations based on optimally tuned range-separated hybrid reveal the presence of intermediate triplet states (Tn, n = 2, 3) in between S1 and T1 for all three PDI-X2 studied in dichloromethane. More importantly, PDI-X2 shows a significantly improved ISC rate than the pristine PDI due to the combined effects stemming from the smaller ΔES-T and the larger SOC. The calculated ISC rates follow the order as PDI-O2 < PDI-S2 < PDI-Se2. These research findings will be helpful in designing PDI based triplet photosensitizers for biomedical, sensing, and photonic applications.
6 citations
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TL;DR: The conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.
Abstract: A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.
Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.
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Figure 1
Ruthenium polypyridyl complexes: versatile visible light photocatalysts.
6,252 citations
4,160 citations
TL;DR: The inactivity of the parent UiO-67 framework and the reaction supernatants in catalytic water oxidation, CO(2) reduction, and organic transformations indicate both the molecular origin and heterogeneous nature of these catalytic processes.
Abstract: Catalytically competent Ir, Re, and Ru complexes H2L1–H2L6 with dicarboxylic acid functionalities were incorporated into a highly stable and porous Zr6O4(OH)4(bpdc)6 (UiO-67, bpdc = para-biphenyldicarboxylic acid) framework using a mix-and-match synthetic strategy. The matching ligand lengths between bpdc and L1–L6 ligands allowed the construction of highly crystalline UiO-67 frameworks (metal–organic frameworks (MOFs) 1–6) that were doped with L1–L6 ligands. MOFs 1–6 were isostructural to the parent UiO-67 framework as shown by powder X-ray diffraction (PXRD) and exhibited high surface areas ranging from 1092 to 1497 m2/g. MOFs 1–6 were stable in air up to 400 °C and active catalysts in a range of reactions that are relevant to solar energy utilization. MOFs 1–3 containing [Cp*IrIII(dcppy)Cl] (H2L1), [Cp*IrIII(dcbpy)Cl]Cl (H2L2), and [IrIII(dcppy)2(H2O)2]OTf (H2L3) (where Cp* is pentamethylcyclopentadienyl, dcppy is 2-phenylpyridine-5,4′-dicarboxylic acid, and dcbpy is 2,2′-bipyridine-5,5′-dicarboxylic a...
1,271 citations
1,265 citations
TL;DR: This review article summarizes some molecular design rationales for triplet PSs, based on the molecular structural factors that facilitate ISC, and the design of transition metal complexes with large molar absorption coefficients in the visible spectral region and long-lived triplet excited states is presented.
Abstract: Triplet photosensitizers (PSs) are compounds that can be efficiently excited to the triplet excited state which subsequently act as catalysts in photochemical reactions. The name is originally derived from compounds that were used to transfer the triplet energy to other compounds that have only a small intrinsic triplet state yield. Triplet PSs are not only used for triplet energy transfer, but also for photocatalytic organic reactions, photodynamic therapy (PDT), photoinduced hydrogen production from water and triplet-triplet annihilation (TTA) upconversion. A good PS should exhibit strong absorption of the excitation light, a high yield of intersystem crossing (ISC) for efficient production of the triplet state, and a long triplet lifetime to allow for the reaction with a reactant molecule. Most transition metal complexes show efficient ISC, but small molar absorption coefficients in the visible spectral region and short-lived triplet excited states, which make them unsuitable as triplet PSs. One obstacle to the development of new triplet PSs is the difficulty in predicting the ISC of chromophores, especially of organic compounds without any heavy atoms. This review article summarizes some molecular design rationales for triplet PSs, based on the molecular structural factors that facilitate ISC. The design of transition metal complexes with large molar absorption coefficients in the visible spectral region and long-lived triplet excited states is presented. A new method of using a spin converter to construct heavy atom-free organic triplet PSs is discussed, with which ISC becomes predictable, C60 being an example. To enhance the performance of triplet PSs, energy funneling based triplet PSs are proposed, which show broadband absorption in the visible region. Applications of triplet PSs in photocatalytic organic reactions, hydrogen production, triplet-triplet annihilation upconversion and luminescent oxygen sensing are briefly introduced.
1,104 citations