Optimizing Upconversion Quantum Yield via Structural Tuning of Dipyrrolonaphthyridinedione Annihilators.

Triplet-triplet annihilation upconversion (TTA-UC) is a photophysical process in which two low-energy photons are converted into one higher-energy photon. This type of upconversion requires two species: a sensitizer that absorbs low-energy light and transfers its energy to an annihilator, which emits higher-energy light after TTA. In spite of the multitude of applications of TTA-UC, few families of annihilators have been explored.

Silver-doped CdSe magic-sized nanocrystals.

Magic-sized nanocrystals (MSNCs) grow via jumps between very specific sizes. This discrete growth is a possible avenue toward monodisperse nanomaterials that are completely identical in size and shape. In spite of this potential, MSNCs have seen limited study and application due to their poor optical properties.

Growth Synchronization and Size Control in Magic-Sized Semiconductor Nanocrystals.

"Magic-sized" nanocrystals (MSNCs) grow in discrete jumps between a series of specific sizes. Consequently, MSNCs have been explored as an alternative route to uniform semiconductor particles, potentially with atomic precision. However, because the growth mechanism has been poorly understood, the best strategies to control MSNC syntheses and obtain desired sizes are unknown.

Core/Shell Magic-Sized CdSe Nanocrystals.

Magic-sized semiconductor nanocrystals (MSNCs) grow via discrete jumps between specific sizes. Despite their potential to offer atomically precise structures, their use has been limited by poor stability and trap-dominated photoluminescence. Recently, CdSe MSNCs have been grown to larger sizes.

prediction of annihilators for triplet-triplet annihilation upconversion auxiliary-field quantum Monte Carlo.

The energy of the lowest-lying triplet state (T1) relative to the ground and first-excited singlet states (S0, S1) plays a critical role in optical multiexcitonic processes of organic chromophores. Focusing on triplet-triplet annihilation (TTA) upconversion, the S0 to T1 energy gap, known as the triplet energy, is difficult to measure experimentally for most molecules of interest. predictions can provide a useful alternative, however low-scaling electronic structure methods such as the Kohn-Sham and time-dependent variants of Density Functional Theory (DFT) rely heavily on the fraction of exact exchange chosen for a given functional, and tend to be unreliable when strong electronic correlation is present.

Understanding Discrete Growth in Semiconductor Nanocrystals: Nanoplatelets and Magic-Sized Clusters.

ConspectusSemiconductor nanocrystals (NCs) fluoresce with a color that strongly depends on their size and shape. Thus, to obtain homogeneous optical properties, researchers have strived to synthesize particles that are uniform. However, because NCs typically grow through continuous, incremental addition of material, slight differences in the growth process between individual crystallites yield statistical distributions in size and shape, leading to inhomogeneities in their optical characteristics.

Bridge Resonance Effects in Singlet Fission.

A major benefit of intramolecular singlet fission (iSF) materials, in which through-bond interactions mediate triplet pair formation, is the ability to control the triplet formation dynamics through molecular engineering. One common design strategy is the use of molecular bridges to mediate interchromophore interactions, decreasing electronic coupling by increasing chromophore-chromophore separation. Here, we report how the judicious choice of aromatic bridges can enhance chromophore-chromophore electronic coupling.

Ultra-fast intramolecular singlet fission to persistent multiexcitons by molecular design.

Singlet fission-that is, the generation of two triplets from a lone singlet state-has recently resurfaced as a promising process for the generation of multiexcitons in organic systems. Although advances in this area have led to the discovery of modular classes of chromophores, controlling the fate of the multiexciton states has been a major challenge; for example, promoting fast multiexciton generation while maintaining long triplet lifetimes. Unravelling the dynamical evolution of the spin- and energy conversion processes from the transition of singlet excitons to correlated triplet pairs and individual triplet excitons is necessary to design materials that are optimized for translational technologies.

Author Correction: Photoredox catalysis using infrared light via triplet fusion upconversion.

In Fig. 1c of this Letter, the orange axis label of the graph should have read 'FDPP upconversion photoluminescence (AU)' instead of 'TTBP upconversion photoluminescence (AU)'. This has been corrected online.

Annihilator dimers enhance triplet fusion upconversion.

Optical upconversion is a net process by which two low energy photons are converted into one higher energy photon. There is vast potential to exploit upconversion in applications ranging from solar energy and biological imaging to data storage and photocatalysis. Here, we link two upconverting chromophores together to synthesize a series of novel tetracene dimers for use as annihilators.

Tunable Emission from Triplet Fusion Upconversion in Diketopyrrolopyrroles.

Optical upconversion based on triplet fusion (TF), also known as triplet-triplet annihilation, is a process by which two or more low-energy photons are converted to one higher energy photon. This process requires two components, a sensitizer which absorbs the incident low-energy photons and an annihilator which emits the higher energy photons. While much attention has been given to the investigation of new types of sensitizers, very little work has been done on the exploration of new annihilators.

Photoredox catalysis using infrared light via triplet fusion upconversion.

Recent advances in photoredox catalysis have made it possible to achieve various challenging synthetic transformations, polymerizations and surface modifications. All of these reactions require ultraviolet- or visible-light stimuli; however, the use of visible-light irradiation has intrinsic challenges. For example, the penetration of visible light through most reaction media is very low, leading to problems in large-scale reactions.

Triplet Harvesting from Intramolecular Singlet Fission in Polytetracene.

Singlet fission (SF), a promising mechanism of multiple exciton generation, has only recently been engineered as a fast, efficient, intramolecular process (iSF). The challenge now lies in designing and optimizing iSF materials that can be practically applied in high-performance optoelectronic devices. However, most of the reported iSF systems, such as those based on donor-acceptor polymers or pentacene, have low triplet energies, which limits their applications.

Tuning Singlet Fission in π-Bridge-π Chromophores.

We have designed a series of pentacene dimers separated by homoconjugated or nonconjugated bridges that exhibit fast and efficient intramolecular singlet exciton fission (iSF). These materials are distinctive among reported iSF compounds because they exist in the unexplored regime of close spatial proximity but weak electronic coupling between the singlet exciton and triplet pair states. Using transient absorption spectroscopy to investigate photophysics in these molecules, we find that homoconjugated dimers display desirable excited-state dynamics, with significantly reduced recombination rates as compared to conjugated dimers with similar singlet fission rates.

Distinct properties of the triplet pair state from singlet fission.

Singlet fission, the conversion of a singlet exciton (S) to two triplets (2 × T), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state (TT). Despite extensive research, the nature of the (TT) state and its spectroscopic signature remain actively debated.

A Direct Mechanism of Ultrafast Intramolecular Singlet Fission in Pentacene Dimers.

Interest in materials that undergo singlet fission (SF) has been catalyzed by the potential to exceed the Shockley-Queisser limit of solar power conversion efficiency. In conventional materials, the mechanism of SF is an intermolecular process (xSF), which is mediated by charge transfer (CT) states and depends sensitively on crystal packing or molecular collisions. In contrast, recently reported covalently coupled pentacenes yield ∼2 triplets per photon absorbed in individual molecules: the hallmark of intramolecular singlet fission (iSF).

Exciton Correlations in Intramolecular Singlet Fission.

We have synthesized a series of asymmetric pentacene-tetracene heterodimers with a variable-length conjugated bridge that undergo fast and efficient intramolecular singlet fission (iSF). These compounds have distinct singlet and triplet energies, which allow us to study the spatial dynamics of excitons during the iSF process, including the significant role of exciton correlations in promoting triplet pair generation and recombination. We demonstrate that the primary photoexcitations in conjugated dimers are delocalized singlets that enable fast and efficient iSF.

Intramolecular Singlet Fission in Oligoacene Heterodimers.

We investigate singlet fission (SF) in heterodimers comprising a pentacene unit covalently bonded to another acene as we systematically vary the singlet and triplet pair energies. We find that these energies control the SF process, where dimers undergo SF provided that the resulting triplet pair energy is similar or lower in energy than the singlet state. In these systems the singlet energy is determined by the lower-energy chromophore, and the rate of SF is found to be relatively independent of the driving force.

Quantitative Intramolecular Singlet Fission in Bipentacenes.

Singlet fission (SF) has the potential to significantly enhance the photocurrent in single-junction solar cells and thus raise the power conversion efficiency from the Shockley-Queisser limit of 33% to 44%. Until now, quantitative SF yield at room temperature has been observed only in crystalline solids or aggregates of oligoacenes. Here, we employ transient absorption spectroscopy, ultrafast photoluminescence spectroscopy, and triplet photosensitization to demonstrate intramolecular singlet fission (iSF) with triplet yields approaching 200% per absorbed photon in a series of bipentacenes.

New form of an old natural dye: bay-annulated indigo (BAI) as an excellent electron accepting unit for high performance organic semiconductors.

A novel electron acceptor was synthesized from one-step functionalization of the readily available indigo dye. The resulting bay-annulated indigo (BAI) was utilized for the preparation of a series of novel donor-acceptor small molecules and polymers. As revealed experimentally and by theoretical calculations, substituted BAIs have stronger electron accepting characteristics when compared to several premier electron deficient building blocks.