Ultrafast Excimer Formation and Solvent Controlled Symmetry Breaking Charge Separation in the Excitonically Coupled Subphthalocyanine Dimer

Roy, Palas; Bressan, Giovanni; Gretton, Jacob; Cammidge, Andrew N.; Meech, Stephen R.

doi:10.1002/ange.202101572

Cited by 7 publications

(6 citation statements)

References 33 publications

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“…Theoretically, the excited states of the molecular dimer can be represented as locally excited singlet (LE) states and charge-separated (CS) states. 31,32 SB-CS processes in weakly coupled dyad and the triad of perylenediimide, 30,33−35 perylene, 26,36,37 BODIPY, 28,38 metallopyrrins, 38−40 bianthryl, 41 subphthalocyanine, 42 and terrylenediimide 43,44 are well explored and documented in the literature. Moreover, probing SB-CS processes in film samples and polymers is an emerging research topic.…”

Section: ■ Introductionmentioning

confidence: 99%

Null Exciton-Coupled Chromophoric Dimer Exhibits Symmetry-Breaking Charge Separation

2021

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A comprehensive understanding of the structure− property relationships in multichromophoric architectures has pushed the limits for developing robust photosynthetic mimics and molecular photovoltaics. The elusive phenomenon of null exciton splitting has gathered immense attention in recent years owing to the occurrence in unique chromophoric architectures and consequent emergent properties. Herein, we unveil the hitherto unobserved null exciton coupling assisted highly efficient photoinduced symmetry-breaking charge separation (SB-CS) in a Greek cross (+)-oriented spiro-conjugated perylenediimide dimer (Sp-PDI 2 ). Quantum chemical calculations have rationalized the infrequent manifestation of null exciton coupling behavior in Sp-PDI 2 . Negligible contribution of long-range Coulombic and shortrange charge-transfer mediated coupling renders a monomer-like spectroscopic signature for Sp-PDI 2 in toluene. The Greek cross (+)-arranged Sp-PDI 2 possesses a selective hole-transfer coupling, facilitating the ultrafast dissociation of null excitons and evolution of the charge-separated state in polar solvents. Radical cationic and anionic spectroscopic signatures were characterized by employing femtosecond transient absorption spectroscopy. The substantial hole transfer electronic coupling and lower activation energy barrier of Sp-PDI 2 accelerated the charge separation rate. The rate of charge recombination (CR) markedly decelerated due to falling into the inverted region of the Marcus parabola, where the driving force of CR is larger than the total reorganization energy for CR. Hence, the ratio of the rates for SB-CS over CR of Sp-PDI 2 exhibited an unprecedently high value of 2647 in acetonitrile. The current study provides impeccable evidence for the role of selective charge filtering in governing efficient SB-CS and thereby novel insights towards the design of biomimics and advanced functional materials.

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Section: ■ Introductionmentioning

confidence: 99%

Null Exciton-Coupled Chromophoric Dimer Exhibits Symmetry-Breaking Charge Separation

2021

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“…Isomerization quantum yields were determined using an in situ irradiation NMR method, also described in detail in the Supporting Information. Methods for broadband transient absorption are described elsewhere 34 and are further detailed in the Supporting Information.…”

Section: ■ Experimental Methodsmentioning

confidence: 99%

Control of Photoconversion Yield in Unidirectional Photomolecular Motors by Push–Pull Substituents

Roy,

Sardjan,

Danowski

et al. 2023

J. Am. Chem. Soc.

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Molecular motors based on the overcrowded alkene motif convert light energy into unidirectional mechanical motion through an excited state isomerization reaction. The realization of experimental control over conversion efficiency in these molecular motors is an important goal. Here, we combine the synthesis of a novel “push–pull” overcrowded alkene motor with photophysical characterization by steady state and ultrafast time-resolved electronic spectroscopy. We show that tuning of the charge transfer character in the excited state has a dramatic effect on the photoisomerization yield, enhancing it to near unity in nonpolar solvents while largely suppressing it in polar solvents. This behavior is explained through reference to solvent- and substituent-dependent potential energy surfaces and their effect on conical intersections to the ground state. These observations offer new routes to the fine control of motor efficiency and introduce additional degrees of freedom in the synthesis and exploitation of light-driven molecular motors.

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“…Symmetry‐breaking charge separation (SB‐CS) reaction is a fundamental process occurring in photosynthetic RCs, which initiates the primary charge separation event of RCs. Upon photoexcitation, the excited state symmetry of the chromophoric pair breaks by environmental or/and structural fluctuations, leading to charge‐separated (CS) state population [11–17] . The strong electronic wavefunction overlap between two bacteriochlorophyll (BChl) units of special pairs results in the mixing of singlet exciton and charge‐transfer (CT) states [18–20] .…”

Section: Introductionmentioning

confidence: 99%

A Symmetry‐Broken Charge‐Separated State in the Marcus Inverted Region

Sebastian

Hariharan

2023

Angew Chem Int Ed

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We report a long‐lived charge‐separated state in a chromophoric pair (DC‐PDI2) that uniquely integrates the advantages of fundamental processes of photosynthetic reaction centers: i) Symmetry‐breaking charge‐separation (SB‐CS) and ii) Marcus‐inverted‐region dependence. The near‐orthogonal bichromophoric DC‐PDI2 manifests an ultrafast evolution of the SB‐CS state with a time constant of τSB-CS ${{\tau }_{{\rm S}{\rm B}-{\rm C}{\rm S}}}$ =0.35±0.02 ps and a slow charge recombination (CR) kinetics with τCR ${{\tau }_{{\rm C}{\rm R}}}$ =4.09±0.01 ns in ACN. The rate constant of CR of DC‐PDI2 is 11 686 times slower than SB‐CS in ACN, as the CR of the PDI radical ion‐pair occurs in the deep inverted region of the Marcus parabola ( -ΔGCR ${{-{\rm \Delta }G}_{{\rm C}{\rm R}}}$ >λ). In contrast, an analogous benzyloxy (BnO)‐substituted DC‐BPDI2 showcases a ≈10‐fold accelerated CR kinetics with τnormalCnormalR/τnormalSnormalB-normalCnormalS ${{\tau }_{{\rm C}{\rm R}}/{\tau }_{{\rm S}{\rm B}-{\rm C}{\rm S}}}$ lowering to ≈1536 in ACN, by virtue of a decreased CR driving force. The present investigation demonstrates a control of molecular engineering to tune the energetics and kinetics of the SB‐CS material, which is essential for next‐generation optoelectronic devices.

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Ultrafast Excimer Formation and Solvent Controlled Symmetry Breaking Charge Separation in the Excitonically Coupled Subphthalocyanine Dimer

Cited by 7 publications

References 33 publications

Null Exciton-Coupled Chromophoric Dimer Exhibits Symmetry-Breaking Charge Separation

Null Exciton-Coupled Chromophoric Dimer Exhibits Symmetry-Breaking Charge Separation

Control of Photoconversion Yield in Unidirectional Photomolecular Motors by Push–Pull Substituents

A Symmetry‐Broken Charge‐Separated State in the Marcus Inverted Region

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