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Two-photon absorption behavior of conjugated oligomers suitable for low colour temperature LEDs.

ABSTRACT: Light emitting diodes (LEDs) with low colour temperatures (CTs) have been proved to be physiologically-friendly light sources. However, there are few reports on the photophysical properties of luminescent materials with CTs lower than candlelight. Herein, one- and two-photon optical properties of four fluorenone-based conjugated oligomers have been systemically investigated. By using a sum-over-essential states (SOS) approach, we obtained the transition dipole moments and two-photon absorption (TPA) cross sections. The triphenylamine end-capped oligomer exhibits reddish orange luminescence with extremely low colour temperature of 1686 K, which is much lower than that of candlelight. Fluorene-ethylene units serving as π-spacers could weaken the role of electron-donating units and effectively enhance the TPA performance of oligomers. Our results provide an effective way for the design and optimization of universal light-emitting material candidates in optoelectronic devices.

SUBMITTER: Huang T

PROVIDER: S-EPMC9912286 | biostudies-literature | 2023 Feb

REPOSITORIES: biostudies-literature

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Two-photon absorption behavior of conjugated oligomers suitable for low colour temperature LEDs.

Huang Tianhao T Jiang Chengzi C Xu Tianning T Ying Jinhui J Lu Ran R Zhou Huipeng H

RSC advances 20230210 8

Light emitting diodes (LEDs) with low colour temperatures (CTs) have been proved to be physiologically-friendly light sources. However, there are few reports on the photophysical properties of luminescent materials with CTs lower than candlelight. Herein, one- and two-photon optical properties of four fluorenone-based conjugated oligomers have been systemically investigated. By using a sum-over-essential states (SOS) approach, we obtained the transition dipole moments and two-photon absorption ( ...[more]

PMID: 36777938

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Project description:Nonlinear optical (NLO) pigments are compounds insoluble in solvents that exhibit phenomena related to nonlinear optical susceptibilities (χ(n) where n = 2,3,...), e.g., two-photon absorption (2PA) which is related to the imaginary part of χ(3). Determination of spectrally-resolved 2PA properties for NLO pigments of macromolecular nature, such as coordination polymers or crosslinked polymers, has long been a challenging issue due to their particulate form, precluding characterizations with standard techniques such as Z-scan. In this contribution, we investigate thus far unknown spectrally-resolved 2PA properties of a new subclass of NLO pigments-crosslinked conjugated polymers. The studied compounds are built up from electron-donating (triphenylamine) and electron-withdrawing (2,2'-bipyridine) structural fragments joined by vinylene (Pol1) or vinyl(4-ethynylphenyl) (Pol2) aromatic bridges. 2PA properties of these polymers have been characterized in broad spectral range by specially modified two-photon excited fluorescence (TPEF) techniques: solid state TPEF (SSTPEF) and internal standard TPEF (ISTPEF). The impact of self-aggregation of aromatic backbones on the 2PA properties of the polymers has been evaluated through extended comparisons of NLO parameters, i.e., 2PA cross sections (σ2) and molar-mass normalized 2PA merit factors (σ2/M) with those of small-molecular model compounds: Mod1 and Mod2. By doing this, we found that the 2PA response of Pol1 and Pol2 is improved 2-3 times versus respective model compounds in the solid state form. Further comparisons with 2PA results collected for diluted solutions of Mod1 and Mod2 supports the notion that self-aggregated structure contributes to the observed enhancement of 2PA response. On the other hand, it is clear that Pol1 and Pol2 suffer from aggregation-caused quenching phenomenon, well reflected in time-resolved fluorescence properties as well as in relatively low values of quantum yield of fluorescence. Accordingly, despite improved intrinsic 2PA response, the effective intensity of two-photon excited emission for Pol1 and Pol2 is slightly lower relative to Mod1 and Mod2. Finally, we explore temperature-resolved luminescence properties under one- (377 nm), two- (820 nm), and three-photon excitation (1020 nm) conditions of postsynthetically Eu3+-functionalized material, Pol1-Eu, and discuss its suitability for temperature sensing applications.

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Two-photon absorption behavior of conjugated oligomers suitable for low colour temperature LEDs.

Publications

Two-photon absorption behavior of conjugated oligomers suitable for low colour temperature LEDs.

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