"Second excimer" luminescence from polymers with sterically hindered naphthalene chromophores

Nakahira, Takayuki; Ishizuka, Satoshi; Iwabuchi, Susumu; Kojima, Kuniharu

doi:10.1021/ma00232a057

Cited by 14 publications

(12 citation statements)

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“…In view of the sterically demanding side chain this finding is not surprising and we note that the effects had no appreciable influence (vide infra) on the relevant physical properties of the homopolymer 1. 48 The thermal properties of the new polymers were studied by thermogravimetric analyses (TGA, Fig. S17 †) and differential scanning calorimetry (DSC, Fig.…”

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confidence: 99%

Light upconversion by triplet–triplet annihilation in diphenylanthracene-based copolymers

et al. 2014

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Low-power light upconversion by triplet-triplet annihilation (TTA-UC) was only recently achieved in glassy materials. Here, a new strategy based on covalent tethering of diphenylanthracene (DPA) emitters to a polymeric backbone is reported. The design aims to optimize the efficiency of this photophysical process in glassy polymeric materials by increasing the emitter content. To that end, DPA molecules were covalently attached to a methacrylate-type monomer and further copolymerized with methylmethacrylate (MMA). Green-to-blue (543 to 440 nm) upconversion was observed at power densities as low as 32 mW/cm 2 in films prepared by solution casting and compression molding (co)polymers containing 8-72 wt% of DPA and palladium octaethyl porphyrin (PdOEP) as a sensitizer (0.03-0.7 wt%). The upconversion intensity was studied as a function of DPA and PdOEP contents and the results suggest that upconversion is optimal for DPA and PdOEP weight fractions of 34 and 0.05 wt% respectively.Several optical upconverting schemes are known to cause an anti-Stokes shift, i.e., the emanating photons have a higher energy than the incident electromagnetic radiation (Fig. 1). [1][2][3] While most upconverting processes require coherent, highpower light produced by lasers (e.g. second-or third-harmonic generation, two-photon absorption emission), upconversion by triplet-triplet annihilation (TTA-UC) is feasible at much lower power densities and with non-coherent, polychromatic excitation. 4,5 The framework is therefore attractive for a range of applications, for example biological imaging and display techniques. [6][7][8][9][10][11][12] Perhaps the biggest promise of TTA-UC is that it can overcome the Shockley-Queisser solar power conversion limit, 13-15 as it permits harnessing photons from the portion of the solar spectrum beyond a solar cell's bandgap. 16,17 The TTA-UC process relies on a series of energy transfer steps between a pair of chromophores, a sensitizer and an emitter ( Fig. 1). 3,[18][19][20][21][22] The sensitizer absorbs incident photons and undergoes intersystem crossing, before a triplet excited state is transferred to the emitter. Two excited emitter molecules then form an encounter complex, and via a triplettriplet annihilation step an emitter singlet excited state is populated. Delayed fluorescence from that singlet manifold ultimately leads to emission of an upconverted photon.Since its discovery in the 1960s, TTA-UC has long been limited to liquid solutions, in which the intermolecular energy transfer steps are facilitated by high degrees of translational and rotational mobility. 5,23 Since solvent-based TTA-UC systems exhibit several drawbacks for practical applications, including limited lifetime 1 and complex implementation, 6,8,[24][25][26][27] the discovery that TTA-UC could be achieved in properly chosen polymers 28 has triggered new interest solid upconverting materials. 7 The first examples of TTA-UC in polymers were based on physical mixtures of sensitizers in conjugated polymers. 3,29 One further improve...

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confidence: 99%

Light upconversion by triplet–triplet annihilation in diphenylanthracene-based copolymers

et al. 2014

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“…84,85 In this context, for example, the adsorption of Np on the surface of silica gel produces a second excimer emission at 375 nm; 86 a second excimer is also observed in polyvinylnaphthalene glass. 74,87 Np-doped amorphous silica glasses show the second excimer peaking at around 380 nm at 0.5 mol/L. 77,88 Thus, the similarity between the Np emission spectra in the FCS and the amorphous silica glasses is indicative of the FCS being glassy, with a concentration of at least 0.5 M. As shown below, the thermal dependence of the fast-frozen samples' luminescence confirms this hypothesis even further.…”

Section: ■ Discussionmentioning

confidence: 76%

“…This property stands in contrast to solutions of nonpolar solvents at high concentrations or an ethanol solution at a low temperature, which allows for excimers with a well-developed π–π overlap; the scenario then results in a distinct excimer emission having large bathochromic shifts around 385–410 nm. , A similar excimer emission peaking at around 400 nm is observed in layers of amorphous Np deposited on either gold or ice at temperatures below 77 K. Excimers are known as stabilized dimers of one excited- and one ground-state molecule, with dissociative ground-state interactions. Conversely, the presence of a second excimer, stabilized in both the ground and excited states, is typical of constrained media with restricted molecular mobility. , In this context, for example, the adsorption of Np on the surface of silica gel produces a second excimer emission at 375 nm; a second excimer is also observed in polyvinylnaphthalene glass. , Np-doped amorphous silica glasses show the second excimer peaking at around 380 nm at 0.5 mol/L. , Thus, the similarity between the Np emission spectra in the FCS and the amorphous silica glasses is indicative of the FCS being glassy, with a concentration of at least 0.5 M. As shown below, the thermal dependence of the fast-frozen samples’ luminescence confirms this hypothesis even further.…”

Section: Discussionmentioning

confidence: 97%

Using Excimeric Fluorescence to Study How the Cooling Rate Determines the Behavior of Naphthalenes in Freeze-Concentrated Solutions: Vitrification and Crystallization

et al. 2020

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We utilized fluorescence spectroscopy to learn about the molecular arrangement of naphthalene (Np) and 1-methylnaphthalene (MeNp) in frozen aqueous solutions. The freezing induces pronounced compound aggregation in the freeze-concentrated solution (FCS) in between the ice grains. The fluorescence spectroscopy revealed prevalent formation of a vitrified solution and minor crystallization of aromatic compounds. The FCS is shown as a specific environment, differing significantly from not only the pure compounds but also the ice surfaces. The results indicate marked disparity between the behavior of the Np and the MeNp; the cooling rate has a major impact on the former but not on the latter. The spectrum of the Np solution frozen at a faster cooling rate (ca 20 K/min) exhibited a temperature-dependent spectral behavior, whereas the spectrum of the solution frozen at a slower rate (ca 2 K/min) did not alter before melting. We interpret the observation through considering the varied composition of the FCS: Fast freezing leads to a higher water content expressed by the plasticizing effect, allowing molecular rearrangement, while slow cooling produces a more concentrated and drier environment. The experiments were conceived as generalizable for environmentally relevant pollutants and human-made freezing.

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“…Like our polymers, this PPE exhibited high quantum yields up to 0.76 in the solid state, which is unusual for a polymer that forms excimers. In addition, poly(vinyl naphthalane),30 containing hindered naphthalene chromophores, formed excimers in solution and in the solid state.…”

Section: Resultsmentioning

confidence: 99%

Poly(phenylene ethynylene)s with alkoxyphenyl substituents

Spiliopoulos¹,

Mikroyannidis²

2002

J. Polym. Sci. A Polym. Chem.

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Two new poly(phenylene ethynylene)s with alkoxyphenyl substituents were synthesized and characterized. The polymers were amorphous, dissolved readily in common organic solvents, and showed glass‐transition temperatures at 162–175 °C. They showed blue photoluminescence both in solution and in the solid state due to the steric interaction between the substituents and the main chain that caused an interruption of the conjugation length. The quantum yields in a tetrahydrofuran solution were up to 0.63. Excimer emission was the dominant product of the photoexcitation of thin films of the polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1449–1455, 2002

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"Second excimer" luminescence from polymers with sterically hindered naphthalene chromophores

Cited by 14 publications

References 1 publication

Light upconversion by triplet–triplet annihilation in diphenylanthracene-based copolymers

Light upconversion by triplet–triplet annihilation in diphenylanthracene-based copolymers

Using Excimeric Fluorescence to Study How the Cooling Rate Determines the Behavior of Naphthalenes in Freeze-Concentrated Solutions: Vitrification and Crystallization

Poly(phenylene ethynylene)s with alkoxyphenyl substituents

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