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1.
Nat Chem ; 11(11): 981-986, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31548665

RESUMO

Quantum teleportation transfers the quantum state of a system over an arbitrary distance from one location to another through the agency of quantum entanglement. Because quantum teleportation is essential to many aspects of quantum information science, it is important to establish this phenomenon in molecular systems whose structures and properties can be tailored by synthesis. Here, we demonstrate electron spin state teleportation in an ensemble of covalent organic donor-acceptor-stable radical (D-A-R•) molecules. Following preparation of a specific electron spin state on R• in a magnetic field using a microwave pulse, photoexcitation of A results in the formation of an entangled electron spin pair D•+-A•-. The spontaneous ultrafast chemical reaction D•+-A•--R• → D•+-A-R- constitutes the Bell state measurement step necessary to carry out spin state teleportation. Quantum state tomography of the R• and D•+ spin states using pulse electron paramagnetic resonance spectroscopy shows that the spin state of R• is teleported to D•+ with high fidelity.

2.
J Am Chem Soc ; 141(31): 12236-12239, 2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31302997

RESUMO

When a molecular electron donor interacts with multiple electron acceptors, quantum coherence can enhance the electron transfer (ET) rate. Here we report photodriven ET rates in a pair of donor-acceptor (D-A) compounds that link one anthracene (An) donor to one or two equivalent 1,4-benzoquinone (BQ) acceptors. Subpicosecond ET from the lowest excited singlet state of An to two BQs is about 2.4 times faster than ET to one BQ at room temperature, but about 5 times faster at cryogenic temperatures. This factor of 2 increase results from a transition from ET to one of two acceptors at room temperature to ET to a superposition state of the two acceptors with correlated system-bath fluctuations at low temperature.

3.
Faraday Discuss ; 216(0): 319-338, 2019 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-31066389

RESUMO

Coherent interactions are prevalent in photodriven processes, ranging from photosynthetic energy transfer to superexchange-mediated electron transfer, resulting in numerous studies aimed towards identifying and understanding these interactions. A key motivator of this interest is the non-statistical scaling laws that result from coherently traversing multiple pathways due to quantum interference. To that end, we employed ultrafast transient absorption spectroscopy to measure electron transfer in two donor-acceptor molecular systems comprising a p-(9-anthryl)-N,N-dimethylaniline chromophore/electron donor and either one or two equivalent naphthalene-1,8:4,5-bis(dicarboximide) electron acceptors at both ambient and cryogenic temperatures. The two-acceptor compound shows a statistical factor of 2.1 ± 0.2 rate enhancement at room temperature and a non-statistical factor of 2.6 ± 0.2 rate enhancement at cryogenic temperatures, suggesting correlated interactions between the two acceptors with the donor and with the bath modes. Comparing the charge recombination rates indicates that the electron is delocalized over both acceptors at low temperature but localized on a single acceptor at room temperature. These results highlight the importance of shielding the system from bath fluctuations to preserve and ultimately exploit the coherent interactions.

4.
J Phys Chem Lett ; 9(16): 4481-4487, 2018 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-30011208

RESUMO

We report femtosecond stimulated Raman spectroscopy (FSRS) measurements on dispersions of CdSe semiconductor nanocrystals (NCs) as a function of particle size and pump fluence. Upon photoexcitation, we observe depletion of stimulated Raman gain corresponding to generation of longitudinal optical (LO) phonons followed by recovery on picosecond timescales. At higher fluences, production of multiple excitons slows recovery of FSRS signals, which we attribute to sustained increases of LO phonon populations due to multiexcitonic Auger heating. Owing to the discretized electronic structure of these NCs, such heating cannot be readily monitored via electronic spectroscopic analysis of high-energy band tails as has been performed for higher-dimensional materials. Notably, recovery timescales exceed those of the biexcitonic Auger recombination process and as such reveal overall thermalization timescales likely owing to an acoustic phonon thermalization bottleneck that dictates the cooling timescale.

5.
J Am Chem Soc ; 140(15): 5290-5299, 2018 04 18.
Artigo em Inglês | MEDLINE | ID: mdl-29589754

RESUMO

We demonstrate that the 10-phenyl-10 H-phenothiazine radical cation (PTZ+•) has a manifold of excited doublet states accessible using visible and near-infrared light that can serve as super-photooxidants with excited-state potentials is excess of +2.1 V vs SCE to power energy demanding oxidation reactions. Photoexcitation of PTZ+• in CH3CN with a 517 nm laser pulse populates a Dn electronically excited doublet state that decays first to the unrelaxed lowest electronic excited state, D1' (τ < 0.3 ps), followed by relaxation to D1 (τ = 10.9 ± 0.4 ps), which finally decays to D0 (τ = 32.3 ± 0.8 ps). D1' can also be populated directly using a lower energy 900 nm laser pulse, which results in a longer D1'→D1 relaxation time (τ = 19 ± 2 ps). To probe the oxidative power of PTZ+• photoexcited doublet states, PTZ+• was covalently linked to each of three hole acceptors, perylene (Per), 9,10-diphenylanthracene (DPA), and 10-phenyl-9-anthracenecarbonitrile (ACN), which have oxidation potentials of 1.04, 1.27, and 1.6 V vs SCE, respectively. In all three cases, photoexcitation wavelength dependent ultrafast hole transfer occurs from Dn, D1', or D1 of PTZ+• to Per, DPA, and ACN. The ability to take advantage of the additional oxidative power provided by the upper excited doublet states of PTZ+• will enable applications using this chromophore as a super-oxidant for energy-demanding reactions.

6.
Faraday Discuss ; 207(0): 217-232, 2018 04 17.
Artigo em Inglês | MEDLINE | ID: mdl-29362748

RESUMO

The ground- and excited-state electronic interactions between the nucleobase analog 8-(4'-phenylethynyl)deoxyguanosine, EG, with natural nucleobases and 7-deazaguanine, as well as between adjacent EG base analogs, have been characterized using a combination of steady-state spectroscopy and time-resolved fluorescence, absorption, and stimulated Raman spectroscopies. The properties of the nucleoside EG-H2 are only weakly perturbed upon incorporation into synthetic DNA hairpins in which thymine, cytosine or adenine are the bases flanking EG. Incorporation of the nucleoside to be adjacent to guanine or deazaguanine results in the formation of short-lived (40-80 ps) exciplexes, the charge transfer character of which increases as the oxidation potential of the donor decreases. Hairpins possessing two or three adjacent EG base analogs display exciton-coupled circular dichroism in the ground state and form long-lived fluorescent excited states upon electronic excitation. Incorporation of EG into the helical scaffold of the DNA hairpins places it adjacent to its neighboring nucleobases or a second EG, thus providing the close proximity required for the formation of exciplex or excimer intermediates upon geometric relaxation of the short-lived EG excited state. The three time-resolved spectroscopic methods employed permit both the characterization of the several intermediates and the kinetics of their formation and decay.


Assuntos
DNA/química , Fluorescência , Guanina/química , Conformação de Ácido Nucleico , Purinas/química , Guanina/análogos & derivados
7.
J Am Chem Soc ; 139(44): 15660-15663, 2017 11 08.
Artigo em Inglês | MEDLINE | ID: mdl-29072446

RESUMO

Controlling spin-spin interactions in multispin molecular assemblies is important for developing new approaches to quantum information processing. In this work, a covalent electron donor-acceptor-radical triad is used to probe spin-selective reduction of the stable radical to its diamagnetic anion. The molecule consists of a perylene electron donor chromophore (D) bound to a pyromellitimide acceptor (A), which is, in turn, linked to a stable α,γ-bisdiphenylene-ß-phenylallyl radical (R•) to produce D-A-R•. Selective photoexcitation of D within D-A-R• results in ultrafast electron transfer to form the D+•-A-•-R• triradical, where D+•-A-• is a singlet spin-correlated radical pair (SCRP), in which both SCRP spins are uncorrelated relative to the R• spin. Subsequent ultrafast electron transfer within the triradical forms D+•-A-R-, but its yield is controlled by spin statistics of the uncorrelated A-•-R• radical pair, where the initial charge separation yields a 3:1 statistical mixture of D+•-3(A-•-R•) and D+•-1(A-•-R•), and subsequent reduction of R• only occurs in D+•-1(A-•-R•). These findings inform the design of multispin systems to transfer spin coherence between molecules targeting quantum information processing using the agency of SCRPs.

8.
J Am Chem Soc ; 139(40): 14265-14276, 2017 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-28880547

RESUMO

Facile exciton transport within ordered assemblies of π-stacked chromophores is essential for developing molecular photonic and electronic materials. Excimer states having variable charge transfer (CT) character are frequently implicated as promoting or inhibiting exciton mobility in such systems. However, determining the degree of CT character in excimers as a function of their structure has proven challenging. Herein, we report on a series of cyclophanes in which the interplanar distance between two phenyl-extended viologen (ExV2+) chromophores is varied systematically using a pair of o-, m-, or p-xylylene (o-, m-, or p-Xy) covalent linkers to produce o-ExBox4+ (3.5 Å), m-ExBox4+ (5.6 Å), and p-ExBox4+ (7.0 Å), respectively. The cyclophane structures are characterized using NMR spectroscopy in solution and single-crystal X-ray diffraction in the solid state. Femtosecond transient mid-IR and stimulated Raman spectroscopies show that the CT contribution to the excimer states formed in o-ExBox4+ and m-ExBox4+ depends on the distance between the chromophores within the cyclophanes, while in the weak interaction limit, as represented by p-ExBox4+ (7.0 Å), the lowest excited singlet state of ExV2+ exclusively photo-oxidizes the p-Xy spacer to give the p-Xy+•-ExV+• ion pair. Moreover, the vibrational spectra of the excimer state show that it assumes a geometry that is intermediate between that of the locally excited and CT states, approximately reflecting the degree of CT character.

9.
Chem Sci ; 8(5): 3821-3831, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28580115

RESUMO

A major goal of artificial photosynthesis research is photosensitizing highly reducing metal centers using as much as possible of the solar spectrum reaching Earth's surface. The radical anions and dianions of rylenediimide (RDI) dyes, which absorb at wavelengths as long as 950 nm, are powerful photoreductants with excited state oxidation potentials that rival or exceed those of organometallic chromophores. These dyes have been previously incorporated into all-organic donor-acceptor systems, but have not yet been shown to reduce organometallic centers. This study describes a set of dyads in which perylenediimide (PDI) or naphthalenediimide (NDI) chromophores are attached to Re(bpy)(CO)3 through either the bipyridine ligand or more directly to the Re center via a pyridine ligand. The chromophores are reduced with a mild reducing agent, after which excitation with long-wavelength red or near-infrared light leads to reduction of the Re complex. The kinetics of electron transfer from the photoexcited anions to the Re complex are monitored using transient visible/near-IR and mid-IR spectroscopy, complemented by theoretical spectroscopic assignments. The photo-driven charge shift from the reduced PDI or NDI to the complex occurs in picoseconds regardless of whether PDI or NDI is attached to the bipyridine or to the Re center, but back electron transfer is found to be three orders of magnitude slower with the chromophore attached to the Re center. These results will inform the design of future catalytic systems that incorporate RDI anions as chromophores.

10.
Anal Chem ; 89(13): 6931-6935, 2017 07 05.
Artigo em Inglês | MEDLINE | ID: mdl-28605893

RESUMO

Femtosecond stimulated Raman spectroscopy (FSRS) is a vibrational spectroscopy technique that has been used in a wide variety of applications: from transient vibrational signature tracking to amplifying weak normal Raman scattering signals. Presented here is an application of FSRS to quantify the differential Raman scattering cross sections (DRSCs) of glucose. In using FSRS to determine the DRSCs of multiple glucose vibrational modes, we demonstrate the applicability of both stimulated Raman loss (SRL) spectroscopy and stimulated Raman gain (SRG) FSRS. Using the two analogous FSRS techniques, SRG and SRL, we determine that the DRSCs of glucose excited at 514.5 nm range from a low of 5.0 ± 1.1 × 10-30 to a high of 8.9 ± 0.9 × 10-30 cm2 molecule-1 sr-1. This work establishes both the compatibility of SRL for measuring DRSCs and values for the DRSC of multiple vibrational modes of glucose.

11.
Chem Sci ; 8(1): 541-549, 2017 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-28616134

RESUMO

The design of efficient hydrogen-evolving photocathodes for dye-sensitized photoelectrochemical cells (DSPECs) requires the incorporation of molecular light absorbing chromophores that are capable of delivering reducing equivalents to molecular proton reduction catalysts at rates exceeding those of charge recombination events. Here, we report the functionalization and kinetic analysis of a nanostructured NiO electrode with a modified perylene-3,4-dicarboximide chromophore (PMI) that is stabilized against degradation by atomic layer deposition (ALD) of thick insulating Al2O3 layers. Following photoinduced charge injection into NiO in high yield, films with Al2O3 layers demonstrate longer charge separated lifetimes as characterized via femtosecond transient absorption spectroscopy and photoelectrochemical techniques. The photoelectrochemical behavior of the electrodes in the presence of Co(ii) and Ni(ii) molecular proton reduction catalysts is examined, revealing reduction of both catalysts. Under prolonged irradiation, evolved H2 is directly observed by gas chromatography supporting the applicability of PMI embedded in Al2O3 as a photocathode architecture in DSPECs.

12.
Nat Commun ; 8: 15171, 2017 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-28516916

RESUMO

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted ∼50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

13.
J Phys Chem A ; 121(23): 4455-4463, 2017 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-28531356

RESUMO

Photoexcitation of electron donor-acceptor molecules frequently produces radical ion pairs with well-defined initial spin-polarized states that have attracted significant interest for spintronics. Transfer of this initial spin polarization to a stable radical is predicted to depend on the rates of the radical ion pair recombination reactions, but this prediction has not been tested experimentally. In this study, a stable radical/electron donor/chromophore/electron acceptor molecule, BDPA•-mPD-ANI-NDI, where BDPA• is α,γ-bisdiphenylene-ß-phenylallyl, mPD is m-phenylenediamine, ANI is 4-aminonaphthalene-1,8-dicarboximide, and NDI is naphthalene-1,4:5,8-bis(dicarboximide), was synthesized. Photoexcitation of ANI produces the triradical BDPA•-mPD+•-ANI-NDI-• in which the mPD+•-ANI-NDI-• radical ion pair is spin coupled to the BDPA• stable radical. BDPA•-mPD+•-ANI-NDI-• and its counterpart lacking the stable radical are found to exhibit spin-selective charge recombination in which the triplet radical ion pair 3(mPD+•-ANI-NDI-•) is in equilibrium with the 3*NDI charge recombination product. Time-resolved EPR measurements show that this process is associated with an inversion of the sign of the polarization transferred to BDPA• over time. The polarization transfer rates are found to be strongly solvent dependent, as shifts in this equilibrium affect the spin dynamics. These results demonstrate that even small changes in electron transfer dynamics can have a large effect on the spin dynamics of photogenerated multispin systems.

14.
J Am Chem Soc ; 139(17): 6120-6127, 2017 05 03.
Artigo em Inglês | MEDLINE | ID: mdl-28436654

RESUMO

The energy landscape of a supramolecular material can include different molecular packing configurations that differ in stability and function. We report here on a thermally driven crystalline order transition in the landscape of supramolecular nanostructures formed by charged chromophore amphiphiles in salt-containing aqueous solutions. An irreversible transition was observed from a metastable to a stable crystal phase within the nanostructures. In the stable crystalline phase, the molecules end up organized in a short scroll morphology at high ionic strengths and as long helical ribbons at lower salt content. This is interpreted as the result of the competition between electrostatic repulsive forces and attractive molecular interactions. Only the stable phase forms charge-transfer excitons upon exposure to visible light as indicated by absorbance and fluorescence features, second-order harmonic generation microscopy, and femtosecond transient absorbance spectroscopy. Interestingly, the supramolecular reconfiguration to the stable crystalline phase nanostructures enhances photosensitization of a proton reduction catalyst for hydrogen production.


Assuntos
Imidas/química , Perileno/química , Catálise , Cristalização , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/química , Estrutura Molecular , Nanoestruturas/química , Tamanho da Partícula , Transição de Fase , Processos Fotoquímicos , Eletricidade Estática , Propriedades de Superfície , Termodinâmica
15.
J Phys Chem A ; 121(11): 2241-2252, 2017 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-28257610

RESUMO

Photoinitiated subnanosecond electron transfer within covalently linked electron donor-acceptor molecules can result in the formation of a spin-correlated radical pair (SCRP) with a well-defined initial singlet spin configuration. Subsequent coherent mixing between the SCRP singlet and triplet ms = 0 spin states, the so-called zero quantum coherence (ZQC), is of potential interest in quantum information processing applications because the ZQC can be probed using pulse electron paramagnetic resonance (pulse-EPR) techniques. Here, pulse-EPR spectroscopy is utilized to examine the ZQC oscillation frequencies and ZQC dephasing in three structurally well-defined D-A systems. While transitions between the singlet and triplet ms = 0 spin states are formally forbidden (Δms = 0), they can be addressed using specific microwave pulse turning angles to map information from the ZQC onto observable single quantum coherences. In addition, by using structural variations to tune the singlet-triplet energy gap, the ZQC frequencies determined for this series of molecules indicate a stronger dependence on the electronic g-factor than on electron-nuclear hyperfine interactions.

16.
J Phys Chem A ; 121(8): 1607-1615, 2017 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-28191955

RESUMO

The use of multiple chromophores as photosensitizers for catalysts involved in energy-demanding redox reactions is often complicated by electronic interactions between the chromophores. These interchromophore interactions can lead to processes, such as excimer formation and symmetry-breaking charge separation (SB-CS), that compete with efficient electron transfer to or from the catalyst. Here, two dimers of perylene bound either directly or through a xylyl spacer to a xanthene backbone were synthesized to probe the effects of interchromophore electronic coupling on excimer formation and SB-CS using ultrafast transient absorption spectroscopy. Two time constants for excimer formation in the 1-25 ps range were observed in each dimer due to the presence of rotational isomers having different degrees of interchromophore coupling. In highly polar acetonitrile, SB-CS competes with excimer formation in the more weakly coupled isomers followed by charge recombination with τCR = 72-85 ps to yield the excimer. The results of this study of perylene molecular dimers can inform the design of chromophore-catalyst systems for solar fuel production that utilize multiple perylene chromophores.

17.
J Am Chem Soc ; 139(5): 2014-2021, 2017 02 08.
Artigo em Inglês | MEDLINE | ID: mdl-28080033

RESUMO

A series of semirigid perylene bisimide (PBI) macrocycles with varied ring size containing two to nine PBI chromophores were synthesized in a one-pot reaction and their photophysical properties characterized by fluorescence, steady-state, and transient absorption spectroscopy as well as femtosecond stimulated Raman spectroscopy. These macrocycles show solvent-dependent conformational equilibria and excited-state properties. In dichloromethane, the macrocycles prevail in wide-stretched conformations and upon photoexcitation exhibit symmetry-breaking charge separation followed by charge recombination to triplet states, which photosensitize singlet oxygen formation. In contrast, in aromatic solvents folding of the macrocycles with a distinct odd-even effect regarding the number of PBI chromophore units was observed in steady-state and time-resolved absorption and fluorescence spectroscopy as well as femtosecond stimulated Raman spectroscopy. These distinctive optical properties are attributable to the folding of the even-membered macrocycles into exciton-vibrational coupled dimer pairs in aromatic solvents. Studies in a variety of aromatic solvents indicate that these solvents embed between PBI dimer pairs and accordingly template the folding of even-membered PBI macrocycles into ropelike folded conformations that give rise to solvent-specific exciton-vibrational couplings in UV-vis absorption spectra. As a consequence of the embedding of solvent molecules in the coiled double-string rope architecture, highly solvent specific intensity ratios are observed for the two lowest-energy exciton-vibrational bands, enabling assignment of the respective solvent simply based on the absorption spectra measured for the tetramer macrocycle.

18.
Inorg Chem ; 55(23): 12281-12289, 2016 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-27934415

RESUMO

Two new covalently linked chromophore-CO2 reduction catalyst systems were prepared using a perylene chromophore and a bis[(dicyclohexylphosphino)ethyl]phenylphosphinopalladium(II) catalyst. The primary goal of this study is to probe the influence of photosensitizer attachment on the electrocatalytic performance. The position either para or meta to the phosphorus on the phenyl group of the palladium complex was linked via a 2,5-xylyl group to the 3 position of perylene. The electrocatalytic CO2 reduction activity of the palladium complex is maintained in the meta-linked system, but is lost in the para-linked system, possibly because of unfavorable interactions of the perylene chromophore with the glassy carbon electrode used. Following selective photoexcitation of the perylene, an enhanced perylene excited-state decay rate was observed in the palladium complexes compared to perylene attached to the free ligands. This decrease is accompanied by formation of the perylene cation radical, showing that electron transfer from perylene to the palladium catalyst occurs. Electron transfer and charge recombination were both found to be faster in the para-linked system than in the meta-linked one, which is attributed to stronger electronic coupling in the former. These results illustrate the need to carefully tune the electronic coupling between a photosensitizer chromophore and the catalyst to promote photodriven electron transfer yet inhibit adverse electronic effects of the chromophore on electrocatalysis.

19.
J Am Chem Soc ; 138(44): 14750-14755, 2016 11 09.
Artigo em Inglês | MEDLINE | ID: mdl-27750426

RESUMO

The dynamics of photoexcited lead-free perovskite films, CH3NH3SnI3, were studied using broadband transient absorption and time-resolved fluorescence spectroscopy. Similar to its lead analogue CH3NH3PbI3, we show that free carrier (electrons and holes) recombination is also the dominant relaxation pathway in CH3NH3SnI3 films. The slow hot carrier relaxation time is 0.5 ps. Long carrier diffusion lengths for electrons (279 ± 88 nm) and holes (193 ± 46 nm) were obtained from fluorescence quenching measurements. We also show that SnF2 doping in the CH3NH3SnI3 film effectively increases the fluorescence lifetime up to 10 times and gives diffusion lengths exceeding 500 nm. These results suggest that the photophysics of CH3NH3SnI3 perovskite are as favorable as those of CH3NH3PbI3, demonstrating that it is a promising nontoxic lead-free replacement for lead iodide perovskite-based solar cells.

20.
J Phys Chem A ; 120(18): 2841-53, 2016 05 12.
Artigo em Inglês | MEDLINE | ID: mdl-27108738

RESUMO

Photoinduced electron transfer reactions in organic donor-acceptor systems leading to long-lived radical ion pairs (RPs) have attracted broad interest for their potential applications in fields as diverse as solar energy conversion and spintronics. We present the photophysics and spin dynamics of an electron donor - electron acceptor - stable radical system consisting of a meta-phenylenediamine (mPD) donor covalently linked to a 4-aminonaphthalene-1,8-dicarboximide (ANI) electron-accepting chromophore as well as an α,γ-bisdiphenylene-ß-phenylallyl (BDPA) stable radical. Selective photoexcitation of ANI produces the BDPA-mPD(+•)-ANI(-•) triradical in which the mPD(+•)-ANI(-•) RP spins are strongly exchange coupled. The presence of BDPA is found to greatly increase the RP intersystem crossing rate from the initially photogenerated BDPA-(1)(mPD(+•)-ANI(-•)) to BDPA-(3)(mPD(+•)-ANI(-•)), resulting in accelerated RP recombination via the triplet channel to produce BDPA-mPD-(3*)ANI as compared to a reference molecule lacking the BDPA radical. The RP recombination rates observed are much faster than those previously reported for weakly coupled triradical systems. Time-resolved EPR spectroscopy shows that this process is also associated with strong spin polarization of the stable radical. Overall, these results show that RP intersystem crossing rates can be strongly influenced by stable radicals nearby strongly coupled RP systems, making it possible to use a third spin to control RP lifetimes down to a picosecond time scale.

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