A highly emissive, optically active poly-(diphenylacetylene) derivative, NpSi*-PDPA, was synthesized by introducing a bulky chiral pendant group into the polymer chain. NpSi*-PDPA exists in a glassy state having a highly disordered and amorphous structure. Hence, the fractional free volume is quite high, i.e., 0.29. NpSi*-PDPA emits a green light in solution and a yellow light in film. This polymer is quite emissive, as the photoluminescence (PL) quantum yield is 56.1% in solution and 6.2% in film, and the PL lifetime is relatively long, 1.71 ns in solution and 1.05 ns in film. NpSi*-PDPA shows the strongest circular dichroism (CD) signal at 384 nm, with a magnitude of circular polarization (g CD ) of 0.90 × 10 −3 and an optical rotation of 110°(4.30 × 10 −3 g mL −1 , in CHCl 3 ). The CD intensity is significantly increased by annealing at 80 °C, reaching an equilibrium at g CD of 7.10 × 10 −3 after 72 h.

Achiral poly(diphenylacetylene)s (PDPAs: pMe3, pEt3, piPr3, pMe2O1, pMe2OD1, and mMe3) with different alkyl side chains at the para or meta position of the side phenyl ring were prepared to examine achiral-to-chiral transformations upon thermal annealing in a chiral solvent. All the para-substituted PDPAs showed significant circular dichroism (CD) enhancement upon annealing, whereas the meta-substituted polymer, mMe3, was inert to the same treatment. To investigate the kinetics, the asymmetric conformational change was monitored by observing the changes in the magnitude of circular polarization (g CD ) or optical rotation. PDPAs with bulkier, round-shaped side groups (pEt3 and piPr3) had greater g CD values at equilibrium than pMe3 with a smaller side group. Moreover, the activation energy for the forward reaction (Ea f ) was lower in the bulkier polymers than in pMe3 owing to enhanced miscibility with the chiral solvent. Similarly, the long alkyl chains of pMe2O1 and pMe2OD1 acted as internal plasticizers to lower their Ea f values relative to that of pMe3, whereas their g CD values at equilibrium were smaller than that of pMe3. The kinetics of the achiral-to-chiral transformation is discussed in detail based on the spectroscopic changes observed during the annealing process.

Two poly­(diphenylacetylene) derivatives containing identical chiral pinanyl groups on the para- and meta-positions of the side phenyl ring were prepared, and their circular dichroism (CD) and photoluminescence (PL) spectra were compared. The magnitudes of circular polarization (g CD) of the para- and meta-polymers were determined to be 3.1 × 10–3 and 1.4 × 10–3, respectively. The PL quantum yield (PLQY) of the para-polymer was much greater (27.8%) than that of the meta-polymer (2.61%). When the two polymers were annealed at 80 °C in toluene, their CD spectra were remarkably enhanced and reached equilibrium at g CD values of 9.6 × 10–3 and 6.0 × 10–3, respectively. The para-polymer was kinetically more favored for the CD enhancement as known from the fact that the activation energies for the reactions of para- and meta-polymers were determined to be 88 and 187 kJ mol–1, respectively. The PLQYs of both polymers were unaffected by annealing.