Molecular Design Strategy for Practical Singlet Fission Materials: The Charm of Donor/Acceptor Decorated Quinoidal Structure

Abstract

Singlet fission (SF) has attracted much attention on account of its great potential applications in high efficiency solar energy conversion. The major roadblock to realize this potential is rooted in the limited scope of practical SF material with strong absorption, suitable triplet energy level, and efficient SF process, as well as good chemical stability. Quinoidal structures feature the innate diradical character, which endows these skeletons SF potential, yet results in some structural instability. Herein, we proposed a novel molecular design strategy for practical SF materials based on donor/acceptor decorated quinoidal structures. This design strategy could allow the quinoidal structures to afford strong absorption, suitable energy levels, and efficient SF properties, as well as excellent stability. Using transient spectroscopy technique and theoretical simulation, a new SF chromophore based on a para-azaquinodimethane skeleton (AQTT) was successfully developed via the proposed design strategy. Ultrafast SF process, 165% triplet yield, suitable triplet energy of ~1.1 eV, strong visible-light-absorption coefficients ~ 10 5 M −1 cm −1 , and good chemical stability, make such material a promising SF candidate toward practical photovoltaic applications.

Conformational distortion-harnessed singlet fission dynamics in thienoquinoid: rapid generation and subsequent annihilation of multiexciton dark state

“…The molar extinction coefficient is at the level of 8 Â 10 4 M À1 cm À1 , which is a key parameter for a practical SF material. 3,7 The doped PMMA film shows a similar absorption line shape with that of solution, and the maxima is slightly blue-shifted to 530 nm. In neat film, the spectrum displays obvious red shift, and a new peak appears around 570 nm, indicating strong intermolecular interaction in a J-type solid aggregate.…”

“…[1][2][3] However, the scope of SF-active materials still remains rather limited due to the specific energetic requirements of E(S 1 ) E 2E(T 1 ), and the complicated modulation of intermolecular interactions. [2][3][4]6,7 Moreover, although SF-based photovoltaic devices with power quantum efficiency (PCE) above 100% have been achieved, 8,9 a limited number of chromophores currently meet the requirements of an ideal SF material for practical application, such as high extinction coefficient, suitable triplet energy, ultrafast, efficient SF property, good stability, etc. [2][3][4]6,7 Therefore, there is a high demand for the development of new SF-capable compounds targeted at practical application.…”

“…[10][11][12][13][14][15][16][17][18] These quinoidal structures feature a distinctive biradical character, which fulfills a basic requirement for the SF process. 7,11,19,20 Varnavski et al reported an intramolecular SF system based on cyanomethylene-terminated TQ compound. 21 For the more easily prepared non-cyanomethylene-terminated TQs (Fig.…”

“…Recently, our group addressed a molecular design strategy for practical SF materials based on donor/acceptor-decorated quinoidal structures. 7 TQ molecule turned out to be a potential candidate based on this design strategy, exhibiting a strong absorption ability, suitable energy levels, and excellent chemical stability. 3,7,26 In the current work, we have systematically investigated the SF dynamics of the TQ system, combining transient absorption (TA) spectroscopy with multi-reference electronic structure calculations (CASPT2/ CASSCF).…”

“…7 TQ molecule turned out to be a potential candidate based on this design strategy, exhibiting a strong absorption ability, suitable energy levels, and excellent chemical stability. 3,7,26 In the current work, we have systematically investigated the SF dynamics of the TQ system, combining transient absorption (TA) spectroscopy with multi-reference electronic structure calculations (CASPT2/ CASSCF). Conformational distortion-harnessed SF dynamics were clearly observed in the studied system, which features the rapid generation and subsequent annihilation of intramolecular multiexciton (ME) dark state with 2 1 A symmetry.…”