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

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 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 ( g em ) and CD ( g abs ) 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 the selective photoscissoring of PSi-S and PSi-R at 313 nm for 60 s. 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 red shifts in the CD and UV-Vis-NIR spectra, which were associated with an enhanced | g abs |, ≈1 × 10 −3 at 715 nm and 0.5 × 10 −3 at 660 nm, compared to the corresponding monomeric value (| g abs | ≈ 0.1 × 10 −3 at 620 nm) obtained using TD-DFT.