scholarly journals Intermolecular vibrations mediate ultrafast singlet fission

2020 ◽  
Vol 6 (38) ◽  
pp. eabb0052 ◽  
Author(s):  
Hong-Guang Duan ◽  
Ajay Jha ◽  
Xin Li ◽  
Vandana Tiwari ◽  
Hanyang Ye ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Potential Energy Surfaces ◽  
Excited Electronic State ◽  
Electronic Spectroscopy ◽  
Low Frequency ◽  
Conical Intersection ◽  
Singlet Fission ◽  
Singlet Exciton ◽  
Spin Singlet ◽  
Triplet Pair

Singlet fission is a spin-allowed exciton multiplication process in organic semiconductors that converts one spin-singlet exciton to two triplet excitons. It offers the potential to enhance solar energy conversion by circumventing the Shockley-Queisser limit on efficiency. We study the primary steps of singlet fission in a pentacene film by using a combination of TG and 2D electronic spectroscopy complemented by quantum chemical and nonadiabatic dynamics calculations. We show that the coherent vibrational dynamics induces the ultrafast transition from the singlet excited electronic state to the triplet-pair state via a degeneracy of potential energy surfaces, i.e., a multidimensional conical intersection. Significant vibronic coupling of the electronic wave packet to a few key intermolecular rocking modes in the low-frequency region connect the excited singlet and triplet-pair states. Along with high-frequency local vibrations acting as tuning modes, they open a new channel for the ultrafast exciton transfer through the resulting conical intersection.

scholarly journals Identification of a triplet pair intermediate in singlet exciton fission in solution

2015 ◽  
Vol 112 (25) ◽  
pp. 7656-7661 ◽  
Author(s):  
Hannah L. Stern ◽  
Andrew J. Musser ◽  
Simon Gelinas ◽  
Patrick Parkinson ◽  
Laura M. Herz ◽  
...  
Keyword(s):  
Critical Role ◽  
Singlet Fission ◽  
Singlet Exciton ◽  
Diffusion Limited ◽  
Spin Singlet ◽  
Triplet Pair ◽  
Spin Triplet ◽  
Singlet Exciton Fission ◽  
Pair State ◽  
Triplet Excitons

Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley–Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spin-singlet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]—tetracene we find rapid (<100 ps) formation of excimers and a slower (∼10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process.

scholarly journals Singlet fission of hot excitons in π -conjugated polymers

2015 ◽  
Vol 373 (2044) ◽  
pp. 20140327 ◽  
Author(s):  
Yaxin Zhai ◽  
Chuanxiang Sheng ◽  
Z. Valy Vardeny
Keyword(s):  
Conjugated Polymers ◽  
Threshold Energy ◽  
High Energy ◽  
Triplet Exciton ◽  
Singlet Fission ◽  
General Process ◽  
Singlet Exciton ◽  
Triplet Pair ◽  
Luminescent Polymer ◽  
Pair State

We used steady-state photoinduced absorption (PA), excitation dependence (EXPA( ω )) spectrum of the triplet exciton PA band, and its magneto-PA (MPA( B )) response to investigate singlet fission (SF) of hot excitons into two separated triplet excitons, in two luminescent and non-luminescent π -conjugated polymers. From the high energy step in the triplet EXPA( ω ) spectrum of the luminescent polymer poly(dioctyloxy)phenylenevinylene (DOO-PPV) films, we identified a hot-exciton SF (HE-SF) process having threshold energy at E ≈2 E T (=2.8 eV, where E T is the energy of the lowest lying triplet exciton), which is about 0.8 eV above the lowest singlet exciton energy. The HE-SF process was confirmed by the triplet MPA( B ) response for excitation at E >2 E T , which shows typical SF response. This process is missing in DOO-PPV solution, showing that it is predominantly interchain in nature. By contrast, the triplet EXPA( ω ) spectrum in the non-luminescent polymer polydiacetylene (PDA) is flat with an onset at E = E g (≈2.25 eV). From this, we infer that intrachain SF that involves a triplet–triplet pair state, also known as the ‘dark’ 2A g exciton, dominates the triplet photogeneration in PDA polymer as E g >2 E T . The intrachain SF process was also identified from the MPA( B ) response of the triplet PA band in PDA. Our work shows that the SF process in π -conjugated polymers is a much more general process than thought previously.

Triplet-Pair States in Organic Semiconductors

2019 ◽  
Vol 70 (1) ◽  
pp. 323-351 ◽  
Author(s):  
Andrew J. Musser ◽  
Jenny Clark
Keyword(s):  
Organic Semiconductors ◽  
First Principles ◽  
Delayed Fluorescence ◽  
Singlet Fission ◽  
Organic Semiconductor Materials ◽  
Materials Research ◽  
Triplet Pair ◽  
The 1960S ◽  
Pair State ◽  
Triplet Excitons

Entanglement of states is one of the most surprising and counterintuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic semiconductor materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which consists of a pair of localized triplet excitons coupled into an overall spin-0, -1, or -2 configuration. The most widely analyzed of these is the spin-0 pair, denoted1(TT), which was initially invoked in the 1960s to explain delayed fluorescence in acene films. It is considered an essential gateway state for triplet-triplet annihilation and the reverse process, singlet fission, enabling interconversion between one singlet and two triplet excitons without any change in overall spin. This state has returned to the forefront of organic materials research in recent years, thanks both to its central role in the resurgent field of singlet fission and to its implication in a host of exotic new photophysical behaviors. Here we review the properties of triplet-pair states, from first principles to recent experimental results.

scholarly journals Singlet fission in thin films of metallo-supramolecular polymers with ditopic thiophene-bridged terpyridine ligands

2017 ◽  
Vol 5 (32) ◽  
pp. 8041-8051 ◽  
Author(s):  
David Rais ◽  
Jiří Pfleger ◽  
Miroslav Menšík ◽  
Alexander Zhigunov ◽  
Pavla Štenclová ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Supramolecular Polymers ◽  
Uv Laser ◽  
Singlet Fission ◽  
Thin Solid Films ◽  
Singlet Exciton ◽  
Solid Films ◽  
Terpyridine Ligands ◽  
Singlet Exciton Fission

Ultrafast singlet exciton fission in thin solid films after UV laser photoexcitation was observed using transient absorption spectroscopy.

scholarly journals Photorelaxation Pathways of 4-(N,N-Dimethylamino)-4′-nitrostilbene Upon S1 Excitation Revealed by Conical Intersection and Intersystem Crossing Networks

Molecules ◽  
2020 ◽  
Vol 25 (9) ◽  
pp. 2230
Author(s):  
Ziyue He ◽  
Ruidi Xue ◽  
Yibo Lei ◽  
Le Yu ◽  
Chaoyuan Zhu
Keyword(s):  
Potential Energy Surfaces ◽  
Branching Ratio ◽  
The Other ◽  
Conical Intersection ◽  
Intersystem Crossing ◽  
Physical Insight ◽  
Quinoid Form ◽  
In Trans ◽  
Crossing Networks ◽  
Energy Surfaces

Multi-state n-electron valence state second order perturbation theory (MS-NEVPT2) was utilized to reveal the photorelaxation pathways of 4-(N,N-dimethylamino)-4′-nitrostilbene (DANS) upon S1 excitation. Within the interwoven networks of five S1/S0 and three T2/T1 conical intersections (CIs), and three S1/T2, one S1/T1 and one S0/T1 intersystem crossings (ISCs), those competing nonadiabatic decay pathways play different roles in trans-to-cis and cis-to-trans processes, respectively. After being excited to the Franck–Condon (FC) region of the S1 state, trans-S1-FC firstly encounters an ultrafast conversion to quinoid form. Subsequently, the relaxation mainly proceeds along the triplet pathway, trans-S1-FC → ISC-S1/T2-trans → CI-T2/T1-trans → ISC-S0/T1-twist → trans- or cis-S0. The singlet relaxation pathway mediated by CI-S1/S0-twist-c is hindered by the prominent energy barrier on S1 surface and by the reason that CI-S1/S0-trans and CI-S1/S0-twist-t are both not energetically accessible upon S1 excitation. On the other hand, the cis-S1-FC lies at the top of steeply decreasing potential energy surfaces (PESs) towards the CI-S1/S0-twist-c and CI-S1/S0-DHP regions; therefore, the initial twisting directions of DN and DAP moieties determine the branching ratio between αC=C twisting (cis-S1-FC → CI-S1/S0-twist-c → trans- or cis-S0) and DHP formation relaxation pathways (cis-S1-FC → CI-S1/S0-DHP → DHP-S0) on the S1 surface. Moreover, the DHP formation could also take place via the triplet relaxation pathway, cis-S1-FC → ISC-S1/T1-cis → DHP-T1 → DHP-S0, however, which may be hindered by insufficient spin-orbit coupling (SOC) strength. The other triplet pathways for cis-S1-FC mediated by ISC-S1/T2-cis are negligible due to the energy or geometry incompatibility of possible consecutive stepwise S1 → T2 → T1 or S1 → T2 → S1 processes. The present study reveals photoisomerization dynamic pathways via conical intersection and intersystem crossing networks and provides nice physical insight into experimental investigation of DANS.

scholarly journals Ultrafast Triplet Pair Separation and Triplet Trapping following Singlet Fission in Amorphous Pentacene Films

2020 ◽  
Vol 124 (43) ◽  
pp. 23567-23578
Author(s):  
Kyle T. Munson ◽  
Jianing Gan ◽  
Christopher Grieco ◽  
Grayson S. Doucette ◽  
John E. Anthony ◽  
...  
Keyword(s):  
Singlet Fission ◽  
Pair Separation ◽  
Triplet Pair

scholarly journals Insights into the Photodecomposition of Azidomethyl Methyl Sulfide: A S2/S1 Conical Intersection on Nitrene Potential Energy Surfaces Leading to the Formation of S-Methyl-N-sulfenylmethanimine

2020 ◽  
Vol 124 (10) ◽  
pp. 1911-1921 ◽  
Author(s):  
Manuel Algarra ◽  
Juan Soto ◽  
Luis Pinto da Silva ◽  
M. Soledad Pino-González ◽  
J. Enrique Rodríguez-Borges ◽  
...  
Keyword(s):  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Conical Intersection ◽  
Methyl Sulfide ◽  
Energy Surfaces

scholarly journals Uncovering dark multichromophoric states in Peridinin–Chlorophyll–Protein

2020 ◽  
Vol 17 (164) ◽  
pp. 20190736
Author(s):  
Elliot J. Taffet ◽  
Francesca Fassioli ◽  
Zi S. D. Toa ◽  
David Beljonne ◽  
Gregory D. Scholes
Keyword(s):  
Crystal Structure ◽  
Excited States ◽  
Quantum Chemical ◽  
Light Harvesting ◽  
Singlet Fission ◽  
Chlorophyll Protein ◽  
Triplet Pair ◽  
A Charge ◽  
Hole Generation ◽  
Chemical Evidence

It has long been recognized that visible light harvesting in Peridinin–Chlorophyll–Protein is driven by the interplay between the bright (S 2 ) and dark (S 1 ) states of peridinin (carotenoid), along with the lowest-lying bright (Q y ) and dark (Q x ) states of chlorophyll- a . Here, we analyse a chromophore cluster in the crystal structure of Peridinin–Chlorophyll–Protein, in particular, a peridinin–peridinin and a peridinin–chlorophyll- a dimer, and present quantum chemical evidence for excited states that exist beyond the confines of single peridinin and chlorophyll chromophores. These dark multichromophoric states, emanating from the intermolecular packing native to Peridinin–Chlorophyll–Protein, include a correlated triplet pair comprising neighbouring peridinin excitations and a charge-transfer interaction between peridinin and the adjacent chlorophyll- a . We surmise that such dark multichromophoric states may explain two spectral mysteries in light-harvesting pigments: the sub-200-fs singlet fission observed in carotenoid aggregates, and the sub-200-fs chlorophyll- a hole generation in Peridinin–Chlorophyll–Protein.

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