Spin-orbit coupling and helical molecular orbitals in oligoyne-bridged bifluorene conformers

Paulius Baronas; Eglė Tankelevičiūtė; Saulius Juršėnas

doi:10.1117/12.2621256

24 May 2022 Spin-orbit coupling and helical molecular orbitals in oligoyne-bridged bifluorene conformers

Paulius Baronas, Eglė Tankelevičiūtė, Saulius Juršėnas

Proceedings Volume 12149, Organic Electronics and Photonics: Fundamentals and Devices III; 1214906 (2022) https://doi.org/10.1117/12.2621256
Event: SPIE Photonics Europe, 2022, Strasbourg, France

Abstract

Helical molecular orbitals forming in oligoynes (chains of sp hybridized carbons) are intriguing for control of electron’s spin in simple organic molecules. Spin-Orbit coupling induced by mixing of orthogonal p electron orbitals leads to enhanced singlet-to-triplet intersystem crossing. However, the role of conformers for spin-orbit coupling is still unclear in oligoyne-bridged systems. Herein, we report a theoretical study of spin-orbit coupling and intersystem crossing rates as a function of axial torsion between bifluorene end-fragments bridged by various length oligoynes. Density functional theory computations revealed that conformers can exist at room temperature due to low torsional barrier. Highest calculated intersystem-crossing rates were found for torsional angles around 30° and agreed well with experimental values. Elongation of oligoyne bridge up to three triple bond fragments leads to steep increase of spin-orbit coupling, and thus, intersystem-crossing rates. Interestingly, at intermediate torsional angles oligoyne bridge allows to maintain high oscillator strength of the lowest singlet transition together with substantial spin-orbit coupling, which is a desirable property for photosensitizer and emitter molecules.

Conference Presentation

Citation Download Citation

Paulius Baronas, Eglė Tankelevičiūtė, and Saulius Juršėnas "Spin-orbit coupling and helical molecular orbitals in oligoyne-bridged bifluorene conformers", Proc. SPIE 12149, Organic Electronics and Photonics: Fundamentals and Devices III, 1214906 (24 May 2022); https://doi.org/10.1117/12.2621256

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