Dynamic Polymer Free Volume Monitored by Single-Molecule Spectroscopy of a Dual Fluorescent Flapping Dopant

Abstract

Single-molecule spectroscopy (SMS) of a dual fluorescent flapping molecular probe (N-FLAP) enabled realtime nanoscale monitoring of local free volume dynamics in polystyrenes. The SMS study was realized by structural improvement of a previously reported flapping molecule by nitrogen substitution, leading to increased brightness (22 times) of the probe. In a polystyrene thin film at the temperature of 5 K above the glass transition, the spectra of a single N-FLAP molecule undergo frequent jumps between short-and long-wavelength forms, the latter one indicating planarization of the molecule in the excited state. The observed spectral jumps were statistically analyzed to reveal the dynamics of the molecular environment. The analysis together with MD and QM/MM calculations show that the excited-state planarization of the flapping probe occurs only when sufficiently large polymer free volume of more than, at least, 280 Å 3 is available close to the molecule, and that such free volume lasts for an average of 1.2 s.

Bridging pico-to-nanonewtons with a ratiometric force probe for monitoring nanoscale polymer physics before damage

“…On the other hand, the difference is the direction of the mechanically induced dynamics; namely, in the rigidochromic probe, the excited-state dynamics from the nearly Franck-Condon emissive geometry to another nonemissive geometry is suppressed in the confined space under mechanical compression. In contrast, the flapping force probe is initially confined with the bent form in a narrow free volume of the polymer materials 67 , but the population of the planarized species increases due to mechanical tension in the stretched polymer chain network (vide infra).…”

Emerging applications of curved aromatic compounds

“…A cyclooctatetraene derivative 2 bearing two phenazine units fused at two nonadjacent double bonds of the cyclooctatetraene ring was described in 2021 by Goto and colleagues [7] (Figure 1B). Compound 2 has a bent geometry in the ground state (S 0 ), and undergoes planarization when excited to the lowest singlet excited state (S 1 ), to produce fluorescence emission with a large Stokes shift of 4800 cm -1 (λ max em = 518 nm).…”

Design strategies and applications of novel functionalized phenazine derivatives: a review

“…Notably, Saito et al 215 developed a flapping fluorescent probe based on phenazine derivative 115 , achieving the real-time monitoring of dynamic free volume in polymers (Scheme 47). 115 showed stronger green fluorescence in CH 2 Cl 2 than FLAP.…”