School of Chemistry - Research Publications

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Author: White, Jonathan × Author: Ghiggino, Kenneth × Start date: 2020 × End date: 2022 ×

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    Photophysics and spectroscopy of 1,2-Benzazulene
    Awuku, S ; Bradley, SJ ; Ghiggino, KP ; Steer, RP ; Stevens, AL ; White, JM ; Yeow, C (Elsevier, 2021-12)
    The electronic spectroscopy and photophysics of 1,2-benzazulene (BzAz) have been examined in solution and in thin solid films, with the objective of comparing its intramolecular and intermolecular excited state decay processes with those of azulene. Unlike azulene, the S2 – S0 absorption and fluorescence spectra exhibit a clear mirror image relationship dominated by a single strong Franck-Condon active progression. Picosecond transient absorption spectra and non-linear S2 fluorescence upconversion experiments reveal lifetimes that follow a well-established energy gap law correlation, indicative of a dominant S2 – S1 decay route. Mechanistic interpretations, including the possibility of S2 singlet fission in aggregates, are discussed.
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    Limitations of conjugated polymers as emitters in triplet-triplet annihilation upconversion
    O'shea, R ; Gao, C ; Bradley, S ; Owyong, TC ; Wu, N ; White, JM ; Ghiggino, KP ; Wong, WWH (ROYAL SOC CHEMISTRY, 2021-11-29)
    Triplet–triplet annihilation upconversion performances for poly(phenylene-vinylene) emitters were investigated through a series of copolymers with bulky sidechains.
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    Revealing the influence of steric bulk on the triplet-triplet annihilation upconversion performance of conjugated polymers
    O'shea, R ; Kendrick, WJ ; Gao, C ; Owyong, TC ; White, JM ; Ghiggino, KP ; Wong, WWH (NATURE PORTFOLIO, 2021-10-01)
    A series of poly(phenylene-vinylene)-based copolymers are synthesized using the Gilch method incorporating monomers with sterically bulky sidechains. The photochemical upconversion performance of these polymers as emitters are investigated using a palladium tetraphenyltetrabenzoporphyrin triplet sensitizer and MEH-PPV as reference. Increased incorporation of sterically bulky monomers leads to a reduction in the upconversion efficiency despite improved photoluminescence quantum yield. A phosphorescence quenching study indicates issues with the energy transfer process between the triplet sensitizer and the copolymers. The best performance with 0.18% upconversion quantum yield is obtained for the copolymer containing 10% monomer with bulky sidechains.
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    The role of conformational heterogeneity in the excited state dynamics of linked diketopyrrolopyrrole dimers†
    Bradley, SJ ; Chi, M ; White, JM ; Hall, CR ; Goerigk, L ; Smith, TA ; Ghiggino, KP (ROYAL SOC CHEMISTRY, 2021-04-21)
    Diketopyrrolopyrrole (DPP) derivatives have been proposed for both singlet fission and energy upconversion as they meet the energetic requirements and exhibit superior photostability compared to many other chromophores. In this study, both time-resolved electronic and IR spectroscopy have been applied to investigate excited state relaxation processes competing with fission in dimers of DPP derivatives with varying linker structures. A charge-separated (CS) state is shown to be an important intermediate with dynamics that are both solvent and linker dependent. The CS state is found for a subset of the total population of excited molecules and it is proposed that CS state formation requires suitably aligned dimers within a broader distribution of conformations available in solution. No long-lived triplet signatures indicative of singlet fission were detected, with the CS state likely acting as an alternative relaxation pathway for the excitation energy. This study provides insight into the role of molecular conformation in determining excited state relaxation pathways in DPP dimer systems.