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Time-evolved, far-red, circularly polarised luminescent polymer aggregates endowed with sacrificial helical Si–Si bond polymers

Abstract

An enantiomeric pair of non-charged, helical dialkylpolysilanes (PSi-R and PSi-S) were endowed with circularly polarised luminescence (CPL) at 700 nm and circular dichroism (CD) at 660 nm when a non-helical poly{[dioctylfluorene]-alt-[bis(thiophenyl)-benzothiazole]} (PF8DBT) formed a hetero-aggregate with PSi-R and PSi-S in a 1-to-1 ratio as repeating units. The initial ultraweak CPL (gem) and CD (gabs) amplitudes of the as-prepared aggregates were magnified up to –0.019 at 706 nm (induced by PSi-S) and +0.017 at 695 nm (induced by PSi-R) after prolonged ageing at ambient temperature for 24 h. These CPL amplitudes were maintained after PSi-S and PSi-R selective photoscissoring at 313 nm for 60 sec. A time-dependent growth behaviour in the hetero-aggregate size (initially ≈ 400 nm; reached ≈ 2000 nm in one day) was observed and characterised using dynamic light scattering (DLS). To investigate the origin of the time-evolution characteristics, the energy potential, dipole moments and CD/UV-Vis-near-infrared (NIR) spectra were simulated upon altering the dihedral angle sets of several model oligomers of PF8DBT using density functional theory (DFT)/time-dependent DFT (TD-DFT) (B3LYP/6-31G(d,p)). An additional Zerner’s Intermediate Neglect of Differential Overlap (ZINDO) calculation qualitatively established that the two hypothetical, chirally dipole-dipole-cancelled, π-π-stacked, slipped dimers cause the red shifts in the CD and UV-Vis-NIR spectra, which were associated with an enhanced |gabs|, ≈ 1 x 10^–3 at 715 nm and 0.5 x 10–3 at 660 nm, compared to the corresponding monomeric value (|gabs| ≈ 0.1 x 10^–3 at 620 nm) obtained using TD-DFT.

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Supplementary files

Publication details

The article was received on 01 Mar 2017, accepted on 17 Apr 2017 and first published on 21 Apr 2017


Article type: Research Article
DOI: 10.1039/C7QM00096K
Citation: Mater. Chem. Front., 2017, Accepted Manuscript
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    Time-evolved, far-red, circularly polarised luminescent polymer aggregates endowed with sacrificial helical Si–Si bond polymers

    M. Fujiki and S. Yoshimoto, Mater. Chem. Front., 2017, Accepted Manuscript , DOI: 10.1039/C7QM00096K

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