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 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 Porous Shape-Persistent Rylene Imine Cages with Tunable Optoelectronic Properties and Delayed Fluorescence

2020 ◽  
Author(s):  
Hsin-Hua Huang ◽  
Kyung Seob Song ◽  
Alessandro Prescimone ◽  
Rajesh Mannancherry ◽  
Ali Coskun ◽  
...  
Keyword(s):  
Excited State ◽  
Electronic Properties ◽  
Green Light ◽  
Delayed Fluorescence ◽  
Optoelectronic Properties ◽  
Covalent Organic Frameworks ◽  
Singlet Fission ◽  
Triplet Pair ◽  
Material Porosity

A simultaneous combination of porosity and tunable optoelectronic properties, common in covalent organic frameworks, are rare in shape-persistent organic cages. Yet, organic cages offer important molecular advantages, the solubility and modularity. Herein, we report the synthesis of a series of chiral imine organic cages with three built-in rylene units by means of dynamic imine chemistry and we investigate their textural and optoelectronic properties. Thereby we demonstrate that the synthesized rylene cages are porous, can be reversibly reduced at accessible potentials, and can absorb from UV up to green light. We also show that they preferentially adsorb CO2 over N2 and CH4 with a good selectivity. In addition, we discovered that the cage incorporating three perylene-3,4:9,10-bis(dicarboximide) units displays a delayed fluorescence, likely as a consequence of formation of a correlated triplet pair, the multiexciton state in singlet fission. Rylene cages thus represent a unique platform to investigate the effect of electronic properties on material porosity and, at the same time, to probe excited-state phenomena in the limit of vanishing interchromophore coupling. <br>

scholarly journals Revealing the contest between triplet-triplet exchange and triplet-triplet energy transfer coupling in correlated triplet pair states in singlet fission

2021 ◽  
Author(s):  
Vibin Abraham ◽  
Nicholas Mayhall
Keyword(s):  
Energy Transfer ◽  
Exchange Interaction ◽  
Entangled State ◽  
Separation Mechanism ◽  
Singlet Fission ◽  
Triplet Energy ◽  
Triplet Pair ◽  
Triplet Energy Transfer ◽  
State 1 ◽  
Pair State

Understanding the separation of the correlated triplet pair state 1(TT) intermediate is critical for leveraging singlet fission to improve solar cell efficiency. This separation mechanism is dominated by two key interactions: (i) the exchange interaction (K) between the triplets which leads to the spin splitting of the biexciton state into 1(TT),3(TT) and 5(TT) states, and (ii) the triplet-triplet energy transfer integral (t) which enables the formation of the spatially separated (but still spin entangled) state 1(T...T). We develop a simple ab initio technique to compute both the biexciton exchange (K) and biexciton transfer coupling. Our key findings reveal new conditions for successful correlated triplet pair state dissociation. The biexciton exchange interaction needs to be ferromagnetic or negligible to the triplet energy transfer for favourable dissociation. We also explore the effect of chromophore packing to reveal geometries where these conditions are achieved for tetracene.

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.

A Marcus-Hush Perspective on Adiabatic Singlet Fission

2019 ◽  
Author(s):  
Timothy Schmidt
Keyword(s):  
Electron Transfer ◽  
Electronic Structure ◽  
Ab Initio ◽  
Density Functional ◽  
Singlet State ◽  
Singlet Fission ◽  
Photo Induced Electron Transfer ◽  
Triplet Pair ◽  
Pair State

<div>Singlet fission is a process whereby a bichromophoric system crosses from an excitonically coupled singlet state to a singlet-coupled triplet pair state. If the electronic structure is described locally, then the process may be described by a formal exchange of electrons. As such, it lends itself to a treatment rooted in the Marcus-Hush description of electron transfer. Here we use ab initio and density functional electronic structure theories to reveal a Marcus-Hush perspective on singlet fission and propose experiments to probe singlet fission in the spirit of photo-induced electron transfer.</div>

scholarly journals Understanding the Bound Triplet-Pair State in Singlet Fission

Chem ◽  
2019 ◽  
Vol 5 (8) ◽  
pp. 1988-2005 ◽  
Author(s):  
Samuel N. Sanders ◽  
Andrew B. Pun ◽  
Kaia R. Parenti ◽  
Elango Kumarasamy ◽  
Lauren M. Yablon ◽  
...  
Keyword(s):  
Singlet Fission ◽  
Triplet Pair ◽  
Pair State

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.

Sign in / Sign up

Export Citation Format

Share Document