A self healing model based on polymer-mediated chromophore correlations

Imaging studies of photodegradation and self-healing in anthraquinone derivative dye-doped PMMA

We study photodegradation and self-healing of nine different anthraquinone-derivatives doped into PMMA using transmission imaging microscopy in search of structure-property relationships of the underlying mechanisms. We find that seven of the nine anthraquinone derivatives display partially reversible photodegradation, with 1,8-dihydroxyanthraquinone (Dantron/Chrysazin) having the best photostability and recovery characteristics of all dyes tested in this study. Based on these measurements we predict that a sample of 1,8-dihydroxyanthraquinone doped into PMMA with a concentration of 9 g l-1 will have a record setting irreversible inverse quantum efficiency of Bε = 4.56 × 109. Additionally, by considering the performance of the different anthraquinone derivatives and their structures, we develop three rules-of-thumb to qualitatively predict the photostability and recovery characteristics of anthraquinone derivatives. These rules-of-thumb will help guide future experiments and molecular modeling in discerning the underlying mechanisms of reversible photodegradation. Finally, we compare our results for disperse orange 11 dye-doped PMMA to the extended Correlated Chromophore Domain Model (eCCDM). While the eCCDM correctly predicts the behavior of the reversible decay component, it fails to correctly predict the behavior of the irreversible degradation component. This implies further modifications to the eCCDM are required.

Recovery of photodegraded rhodamine 6g in ester-containing polymer matrices

Self-healing, rhodamine 6g, dye-doped polymers are reported. The amplified spontaneous emission (ASE) photodegrades after repeated exposure to 532 nm laser light at 10 Hz. Recovery of the ASE signal is observed in dye-doped thermoplastic polyurethane and glycol-modified poly(ethylene terephthalate); both polymers contain repeating ester groups in their backbone. The polymer ester groups are hypothesized to mediate the full recovery of rhodamine 6g from a photodegraded state. A small amount of ASE recovery after photodegradation is observed in dye-doped poly(vinyl alcohol), >98% hydrolyzed, where conversion of rhodamine 6g from a long-lived dark state contributes to the majority of the increased ASE signal in poly(vinyl alcohol) while small amounts of recovery from interactions with residual acetate groups are also possible.

Disperse red 15 (DR15) impedes biofilm formation of uropathogenic Escherichia coli

Catheter associated urinary tract infection (CAUTI) is a highly prevalent hospital-acquired infection that is predominantly caused by uropathogenic Escherichia coli (UPEC). It adheres on catheter surface using type I pili as the initial step of pathogenesis that progresses to form biofilm. In this study, potential inhibitors against FimH adhesin of type I pili were screened computationally that yielded ten compounds. These were further validated in vitro against adhesion and biofilm formation. The compounds, 1-Amino-4-hydroxyanthraquinone (Disperse Red 15 or DR15) and 4-(4'-chloro-4-biphenylylsulfonylamino) benzoic acid (CB1) impaired adhesion and biofilm formation without inhibiting the planktonic growth. Also, both compounds inhibited cell assemblages like autoaggregation and swarming motility by unknown mechanisms. DR15 was further derivatised into N-(4-hydroxy-9,10-dioxo-9,10-dihydroanthracen-1-yl) undec-10-enamide that self-assembled with linseed oil, which was used as the coating material on urinary Foley catheters. The thin-film coating on the catheter did not leach when incubated in artificial urine and effectively restricted biofilm formation of UPEC. Altogether, the thin-film coating of urinary catheter with DR15 inhibited biofilm formation of UPEC and this application could potentially help to reduce CAUTI incidents in healthcare facilities.

Research Progress on Photosensitizers for DSSC

Dye sensitized solar cells (DSSC) are considered one of the most promising photovoltaic technologies as an alternative to traditional silicon-based solar cells, for their compatibility with low-cost production methods, their peculiar optical and mechanical properties and the high indoor efficiency. Photosensitizers represent one of the most important components of a DSSC device and probably the most thoroughly investigated in the last twenty years, with thousands of dyes that have been proposed and tested for this kind of application. In this review we aimed to provide an overview of the three main classes of DSSC photosensitizers, namely ruthenium(II) polypyridyl complexes, Zn-porphyrin derivatives and metal-free organic dyes. After a brief introduction about the architecture and operational principles of a DSSC and the state of the art of the other main components of this type of device, we focused our discussion on photosensitizers. We have defined the numerous requirements DSSC photosensitizers should satisfy and have provided an overview of their historical development over the years; by examining specific dyes reported in the literature, we attempted to highlight the molecular design strategies that have been established for the optimization of their performance in real devices both in terms of efficiency (which recently reaches an outstanding 14.3%) and operational stability. Finally, we discussed, in the last section, the possible future developments of this intriguing technology.

Spectroscopic studies of the mechanism of reversible photodegradation of 1-substituted aminoanthraquinone-doped polymers

The mechanism of reversible photodegradation of 1-substituted aminoanthraquinones doped into poly(methyl methacrylate) and polystyrene is investigated. Time-dependent density functional theory is employed to predict the transition energies and corresponding oscillator strengths of the proposed reversibly and irreversibly damaged dye species. Ultraviolet-visible and Fourier transform infrared (FTIR) spectroscopy are used to characterize which species are present. FTIR spectroscopy indicates that both dye and polymer undergo reversible photodegradation when irradiated with a visible laser. These findings suggest that photodegradation of 1-substituted aminoanthraquinones doped in polymers originates from interactions between dyes and photoinduced thermally degraded polymers, and the metastable product may recover or further degrade irreversibly.

Imaging studies of temperature dependent photodegradation and self-healing in disperse orange 11 dye-doped polymers

Using confocal transmission imaging microscopy, we measure the temperature dependence of photodegradation and self-healing in disperse orange 11 (DO11) dye-doped (poly)methyl-methacrylate (PMMA) and polystyrene (PS). In both dye-doped polymers, an increase in sample temperature results in a greater photodegradation rate and degree of degradation, while also resulting in a slower recovery rate and larger recovery fraction. These results confirm the temperature dependence predictions of the modified correlated chromophore domain model (mCCDM) [B. R. Anderson and M. G. Kuzyk, Phys. Rev. E 89, 032601 (2014)]. Additionally, using quantitative fitting of the imaging data for DO11/PMMA, we determine the domain density parameter to be ρ = 1.19 (±0.25) × 10(-2) and the domain free energy advantage to be λ = 0.282 ± 0.015 eV, which are within the uncertainty of the values previously determined using amplified spontaneous emission as the probe method [S. K. Ramini et al., Polym. Chem. 4, 4948 (2013)]. Finally, while we find photodegradation and self-healing of DO11/PS to be qualitatively consistent with the mCCDM, we find that it is quantitatively incompatible with the mCCDM as recovery in DO11/PS is found to behave as a stretched (or double) exponential as a function of time.

Self-healing organic-dye-based random lasers

One of the primary difficulties in the implementation of organic-dye-based random lasers is the tendency of organic dyes to irreversibly photodecay. In this Letter, we report the observation of "reversible" photodegradation in a Rhodamine 6G and ZrO2 nanoparticle-doped polyurethane random laser. We find that during degradation, the emission broadens, redshifts, and decreases in intensity. After degradation, the system is observed to self-heal leading to the emission returning to its pristine intensity, giving a recovery efficiency of 100%. While the peak intensity fully recovers, the process is not strictly "reversible", as the emission after recovery is still found to be broadened and redshifted. The combination of the peak emission fully recovering and the broadening of the emission leads to a remarkable result: the random laser cycled through degradation, and recovery has a greater integrated emission intensity than the pristine system.

Generalizing the correlated chromophore domain model of reversible photodegradation to include the effects of an applied electric field

All observations of photodegradation and self-healing follow the predictions of the correlated chromophore domain model [Ramini et al., Polym. Chem. 4, 4948 (2013)]. In the present work, we generalize the domain model to describe the effects of an electric field by including induced dipole interactions between molecules in a domain by means of a self-consistent field approach. This electric field correction is added to the statistical mechanical model to calculate the distribution of domains that are central to healing. Also included in the model are the dynamics due to the formation of an irreversibly damaged species, which we propose involves damage to the polymer mediated through energy transfer from a dopant molecule after absorbing a photon. As in previous studies, the model with one-dimensional domains best explains all experimental data of the population as a function of time, temperature, intensity, concentration, and now applied electric field. Though the precise nature of a domain is yet to be determined, the fact that only one-dimensional domain models are consistent with observations suggests that they might be made of correlated dye molecules along polymer chains. Furthermore, the voltage-dependent measurements suggest that the largest polarizability axis of the molecules are oriented perpendicular to the chain.