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

Abstract

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. INTRODUCTIONOrganic materials have a broad range of applications such as high-resolution fluorescence microscopy [1][2][3][4][5][6][7], second harmonic generation (SHG) microscopy [8][9][10][11][12], dye sensitized and polymer solar cells [13][14][15][16][17], solid state dye/organic lasers [18][19][20], and organic light emitting diodes [21,22], to name a few. Photostability of organic compounds and polymers is often a requirement for applications incorporating light-matter interaction [2-4, 6, 8, 18-20, 23-30]. When a material undergoes photodegradation, its characteristic properties deteriorate over time, which is referred to as decay; the reverse change in the characteristic properties of the material is referred to as recovery. Though photodegradation is often irreversible, the recovery process has been observed from a large variety of materials, typically involving polymers and often together with dyes, with various experimental techniques when the photodegraded materials are kept in dark for a long enough time, typically hours to days [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44].Amplified spontaneous emission (ASE) of disperse orange 11 (DO11) doped in poly(methyl methacrylate) (PMMA) bulk sample was observed to fully recover in the dark about 40 hours after photodegradation when irradiated with a 532 nm second harmonic Nd:YAG picosecond laser [33]. This self-healing phenomenon was also observed in various anthraquinone derivatives doped in PMMA and polystyrene (PS) thin films [41,42] and DO11 doped in MMA-styrene copolymers thin films [42,45] probed with transmittance image microscopy and ASE. The photodegraded thin film samples are often observed to recover partially, which suggests there exists both reversible and irreversible photodegradation. The lack of evidence for linear dichroism during photodegradation measurements eliminates orientational hole burning as the mechanism causing reversible photodegra- [38,42,46,[50][51][52][53][54], they have failed to elucidate the underlying mechanism.Several hypotheses of the mechanism responsible for reversible photodegradation in DO11/PMMA have been proposed, including intramolecular proton transfer and ...

Optical Characterization of Doped Thermoplastic and Thermosetting Polymer-Optical-Fibers

“…As Figure 11b shows, there is a partial recovery in the fluorescence capacity during the rest time both in the thermoplastic POF and in the thermosetting one: the emission intensities are, respectively, 16% and 22.3% higher right after the rest. This partial recovery has also been reported for other types of doped fibers and thin films, which suggests that there exist some reversible photodegradation processes [43]. Despite the partial recovery in the emission intensities during the rest time in both types of fibers, the changes in the emission average wavelength and in the spectral width are insignificant with respect to the values obtained just before the rest (see Figure 11d,f).…”

Molecular structure and reversible photodegradation in anthraquinone dyes

“…However, Hung has proposed that in similar dyes, these observations might be consistent with a Gaussian distribution of barrier energies, which yields a stretched exponential distribution of the time constants. [27] The trends of the data here seem to contradict this hypothesis.…”

Photochemical Properties and Stability of BODIPY Dyes

“…Therefore, for the hypothetical mechanisms also, the theoretical calculations were performed in order to confirm the reason of the absorption decrease over long irradiation times. Due to the complicated pathways of the possible photofragmentation processes, the theoretical analysis was limited to the investigation of the absorption spectrum of the photodegradation products, which are expected to be observed experimentally after the irradiation [62]. This is of importance for the possible biomedical application of the analyzed BODIPY compounds, which could, in general, decompose with the creation of any products detrimental for living organisms.…”