Exciton Diffusion, Antenna Effect, and Quenching Defects in Superficially Dye-Doped Conjugated Polymer Nanoparticles

Abstract

Energy transfer (ET) in conjugated polymer nanoparticles (CPNs) is a critical process that affects the performance of these materials in diverse applications such as biological−chemical− physical sensing, imaging, photovoltaics, and phototherapy. Herein, we performed an in-depth study of ET in the CPNs of poly(9,9dioctylfluorene-altbenzothiadiazole) (F8BT) superficially doped with well-controlled amounts of rhodamine B (RhB) dye using a combined experimental and theoretical approach. In these particles, the conjugated polymer acts as the excitation energy donor, whereas adsorbed dye molecules and non-emissive quenching defect sites (Q) act as energy acceptors. Fitting of simulated polymer emission to experimental data provided the intrinsic exciton diffusion length (L d = 8.6 nm) of the polymer and the mean number of quenching defects per particle ρ = × − ( 1.56 10 defects/nm ) Q 2 2 . Importantly, results provide for the first time sound evidence indicating that quenching defect centers are superficially, rather than volumetrically, distributed in these CPNs. The so-called antenna effect (AE), a parameter frequently used to characterize the ET process in donor−acceptor multichromophoric systems, was also calculated. The AE in these CPNs takes a maximum value of ∼40, which compares well with the values reported for similar systems. The developed model (and associated computational Python code) represents a significant improvement over previous models/codes by correcting inconsistencies and successfully simulating ET processes in dye-doped CPNs taking into account: exciton diffusion, ET to nonemissive quenching defect centers, ET to dye dopants, spatial distribution of dyes and defects within CPNs, and individual particle excitation probability among other parameters. The model calculates the ensemble-averaged, time-resolved, and time-averaged emission intensity of CPNs and dye dopants for specific CPN size distributions, allowing for direct comparison with experimental bulk measurements. We envisage that the presented improvements in both the theoretical model and the experimental strategy will prove useful in the study and design of new dye-doped CPNs for practical applications.

Conjugated Polymer Nanoparticles as Visible Light Panchromatic Photoinitiators for 3D Printing of Acrylic Hydrogels

“…Note that ⟨τ⟩ the experimental lifetimes of CPNs are always 1 order of magnitude shorter than those of the corresponding CPs in THF, which is consistent with the previously mentioned Φ f trend. This phenomenon has been previously studied in detail, and attributed to the existence of defect sites in CPNs that efficiently quench the (Frenkel-type) excitons in CPNs …”

“…Using typical CPs densities (∼0.7–0.9 g/cm 3 ) and the reported above, it is possible to estimate that a CPs dispersion of ∼10 mg/L is equivalent to a [CPNs] ∼10 –8 –10 –9 M . Hence, taking into account the ε a max values in Table , it is possible to calculate that the corresponding CPNs’ molar absorption coefficients (ε) are approximately in the range of 10 7 –10 10 M –1 cm –1 .…”

“…Using typical CPs densities (∼0.7−0.9 g/cm 3 ) and the d h reported above, it is possible to estimate that a CPs dispersion of ∼10 mg/L is equivalent to a [CPNs] ∼10 −8 −10 −9 M. 20 Hence, taking into account the ε a max values in Table 1, it is possible to calculate that the corresponding CPNs' molar absorption coefficients (ε) are approximately in the range of 10 7 −10 10 M −1 cm −1 . These values are many orders of magnitude greater than those observed for water-soluble typical type I or type II visible light-excitable photoinitiators.…”

“…This phenomenon has been previously studied in detail, and attributed to the existence of defect sites in CPNs that efficiently quench the (Frenkel-type) excitons in CPNs. 20 Conjugated Polymer Nanoparticles (CPNs) as PIS for the Photopolymerization of Acrylic Monomers in Aqueous Media. The potential of CPNs to photoinitiate radical polymerization was first explored using acrylamide (AAm) as a monomer in water in deoxygenated solutions.…”

Luminescence-enhanced conjugated polymer dots through thermal treatment for cell imaging

“…Meanwhile, the polymer itself will have certain chemical defects, resulting in irregular, disordered and defective stacked conjugated polymer chains. [33][34][35] For example, tetrahedral defects are often observed in polymer particles prepared from polyethylene based polymers. 36 These defects lead to unstable luminescence, low fluorescence brightness, and a broad emission peak width and low light stability, which may limit the further application of Pdots in biological imaging.…”