Singlet fission in nanoaggregate of bis(phenylethynyl) derivative of benzene (BPEB): High energy triplet exciton generation with >100 % yield

Photophysics of Dibenzo[a,l]pentacene upon Monomer to Thin Film Transformation: Enhanced Visible Light Absorption and Ultrafast Singlet Fission

“…Singlet fission (SF) is a sought-after property of organic semiconductors having potential for overcoming the Shockley–Quisser efficiency limit of organic photovoltaics. − It is a process where a photogenerated singlet exciton is converted to two triplet excitons resulting in more than 100% excitonic yield, − paving the way for fabrication of efficient organic solar cells. However, this property is restricted to only a few classes of organic molecules due to stringent energetic and molecular coupling criteria. − Efficient SF is exhibited by molecular systems having the lowest excited singlet (S 1 ) energy levels twice that of the lowest triplet (T 1 ) energy level, that is, it must fulfill E­(S 1 ) ≥ 2E­(T 1 ) energetic criteria. − In addition, SF involves an electron spin-exchange process, which requires an orbital overlap and introduces the strict requirement of strong intermolecular coupling. , Polyacenes, carotenoids, isobenzofurans, perylenebisimides, terylenes, and diketopyrrolopyrrole derivatives are mostly reported to exhibit this exceptional property. − …”

Ultrafast Dynamics of the 9,10-Bis[(triisopropylsilyl)ethynyl]anthracene Nanoaggregate and Thin Film: Influence of the Molecular Packing and Sample Morphology on Singlet Fission and Excimer Formation

“…As the number of fused benzene rings increases, SF energetics become isoergic and then exoergic, favoring ultrafast SF dynamics in larger polyacenes. − The increase in the number of fused benzene rings in polyacenes results in incremental stabilization of both S 1 and T 1 energy levels. − Thus, even though larger polyacenes are reported to exhibit efficient and ultrafast SF, the energy of SF-generated triplet excitons becomes lower, limiting the scope of harvesting them as charge carriers. A higher energy T 1 level is desirable for an efficient energy extraction process, e.g., sensitization of silicon or low-band gap semiconducting quantum dots .…”

Rapid Computational Approach Towards Designing Singlet-Fission Chromophores by Tuning the Diradical Character of Heteroatom-Doped Polycyclic Aromatic Hydrocarbons Using the Atom-Specific Fukui Function

“…Slight endoergicity would be desirable for photovoltaic applications; 8 despite that, both endoergicity and isoergicity have been shown to result in depletion of the T 1 state population via triplet− triplet annihilation (TTA). 9,10 Too much exoergicity is also undesired as this could lead to thermal wastage and would retard the rate of SF. 11 These criteria posit the condition 2E(T 1 )− E(S 1 ) ≤ 0.…”

“…Of the numerous requirements for facilitating effective SF in a molecular system, the condition that double the energy of the T 1 state be slightly lesser than or equal to the energy of the S 1 state is the prime reason that renders the SF process slightly exoergic or nearly isoergic. Slight endoergicity would be desirable for photovoltaic applications; despite that, both endoergicity and isoergicity have been shown to result in depletion of the T 1 state population via triplet–triplet annihilation (TTA). , Too much exoergicity is also undesired as this could lead to thermal wastage and would retard the rate of SF . These criteria posit the condition 2 E (T 1 )– E (S 1 ) ≤ 0.…”