Singlet exciton fission (SEF) is in the limelight due to its potential to increase the solar cell efficiency from 33% to 44%.1, 2 SEF is a spin-allowed process when one excited state chromophore shares its energy with a neighboring ground state chromophore to produce two triplet excited states that reside intramolecularly or intermolecularly via a correlated triplet pair 1(TT) having a singlet multiplicity. Efficient SEF molecules achieve 1(TT) state much faster than the lowest vibrational energy level of the singlet emissive state due to the overlap of 1(TT) state and vibrational energy levels. Typically, rapid conversion from the initial excited state to the 1(TT) state results in a change in the dipole moment and symmetry of the excited electron cloud which is sensitive to nonlinear polarization of the molecule. However, a correlation between the nonlinear optical properties and intramolecular SEF efficiencies has not been reported yet. In this study, we investigate the aforementioned correlation using advanced DFT calculations. Geometry optimization was sequentially carried out at Hartree-Fock 3-21G, B3LYP 6-31G and 6-311G levels of theory. Then, electric field induced second harmonic generation (EFISHG), which is a third-order nonlinear optical property, was calculated on the optimized structures within a range of 600-1200 nm wavelengths using DFT calculations at 6-311G level of theory. A strong peak in the EFISHG plot indicates the strong third-order nonlinear polarization of the molecule that facilitates the fast formation of 1(TT) state. Bipentacene1 (n=0) BP0 which has a SEF efficiency of 200% shows a large EFISHG value of |2.0 x 10-28| esu at 700 nm wavelength. Based on the observations we have, a significant correlation between singlet fission excitation wavelength and EFISHG wavelength was observed.

Investigating the correlation between the nonlinear optical properties and singlet fission (SEF) efficiencies using advanced density functional theory (DFT) calculations

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.