Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission - Aix-Marseille Université Access content directly
Journal Articles Journal of Physical Chemistry Letters Year : 2023

Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission

Abstract

The experimental measurement of the photophysical and chiroptical properties of helicene-based π-conjugated emitters with electron-accepting (-CN, -py, -NO(2)) or donating (TMS, NMe(2), NH(2)) moieties is reported at low temperature (77 K). The samples exhibit strong circularly polarized phosphorescence in frozen solution of 2-MeTHF, with a luminescence dissymmetry factor reaching 1.6 × 10(-2) and a lifetime of over 0.46 s for the most active molecule, the nitro compound. The theoretical investigation shows that although the singlet (S(1)) and triplet (T(1)) excited-state emissions mainly arise from the helicene core, the rotatory strengths of the spin-allowed versus spin-forbidden emission have opposite signs. Further analysis of the spin-orbit coupling matrix elements shows that there is no strong mixing between S(1) and T(1), justifying the different signs of the rotatory strengths. In the case of the nitro compound, the enhanced phosphorescence emission is due to an efficient intersystem crossing.
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Dates and versions

hal-03971815 , version 1 (19-02-2023)

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Kais Dhbaibi, Pierpaolo Morgante, Nicolas Vanthuyne, Jochen Autschbach, Ludovic Favereau, et al.. Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission. Journal of Physical Chemistry Letters, 2023, pp.1073-1081. ⟨10.1021/acs.jpclett.2c03831⟩. ⟨hal-03971815⟩
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