Dielectric Dependence of Single-Molecule PhotoluminescenceIntermittency: Nile Red in Poly(vinylidene fluoride).

Thedependence of single-molecule photoluminescence intermittency(PI) or “blinking” on the local dielectric constant(ε) is examined for nile red (NR) in thin films of poly(vinylidenefluoride) (PVDF). In previous studies, variation of the local dielectricconstant was accomplished by studying luminophores in chemically andstructurally different hosts. In contrast, the NR/PVDF guest–hostpair allows for the investigation of PI as a function of ε whilekeeping the chemical composition of both the luminophore and hostunchanged. The solvatochromic properties of NR are used to measurethe local ε, while fluctuations in NR emission intensity overtime provide a measure of the PI. PVDF is an ideal host for this studybecause it provides submicron-sized dielectric domains that vary fromnonpolar (ε ≈ 2) to very polar (ε ≈ 70).The results presented here demonstrate that the local dielectric environmentcan have a pronounced effect on PI. We find that the NR emissive eventsincrease 5-fold with an increase in ε from 2.2 to 74. A complexdependence on ε is also observed for NR nonemissive event durations,initially increasing as ε increases from 2.2 to 3.4 but decreasingin duration with further increase in ε. The variation in emissiveevent durations with ε is reproduced using a photoinduced electron-transfermodel involving electron transfer from NR to PVDF. In addition, anincrease in NR photostability with an increase in ε is observed,suggesting that the dielectric environment plays an important rolein defining the photostability of NR in PVDF. [ABSTRACT FROM AUTHOR]