Highly Emissive Excimers by 2D Compression of Conjugated Polymers

Koo, Byungjin; Swager, Timothy M.

doi:10.1021/acsmacrolett.6b00491

Cited by 10 publications

(15 citation statements)

References 23 publications

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“…30 The change of stacking direction and distance often brings different emission efficiency. 31 Therefore, tunable conformation and controlled crystal growth are crucial for understanding the phosphorescence emission efficiency of organic species.…”

Section: Introductionmentioning

confidence: 99%

“…Zhang et al reported that coassembled crystals could show higher emission efficiency than the single molecular crystals . The change of the stacking direction and distance often leads to different emission efficiencies . Therefore, tunable conformation and controlled crystal growth are crucial for understanding the phosphorescence emission efficiency of organic species.…”

Section: Introductionmentioning

confidence: 99%

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Multidimensional Structure Conformation of Persulfurated Benzene for Highly Efficient Phosphorescence

Baryshnikov

Kuklin

et al. 2020

ACS Appl. Mater. Interfaces

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It is a challenge to acquire, realize and comprehend highly emissive phosphorescent molecules. Herein, we report that, using persulfurated benzene compounds as models, phosphorescence can be strongly enhanced through the modification of molecular conformation and crystal growth conditions. By varying the peripheral groups in these compounds, we were able to control their molecular conformation and crystal growth mode, leading to one-(1D), two-(2D) and three-dimensional (3D) crystal morphologies. Two kinds of typical molecular conformations were separately obtained in these crystals through substituent group control or solvent effect. Importantly, a symmetrical 3,3-conformer exhibits that planar central benzene ring prefers a 3D-type crystal growth mode, demonstrating high 2 phosphorescence efficiency. Such outcome is attributed to strong crystal protection effect of 3D crystal and bright global minimum (GM) boat-like T1 state of the symmetrical 3,3-conformer.The conformation studies further reveal small deformation of the inner benzene ring in both singlet and triplet states. The GM boat-like T1 state is indicated by theoretical calculations, which is far away from the conical intersection (CI) point between the S0 and T1 potential energy surface. Meanwhile, the small energy gap between S1 and T1 states and the considerable spinorbit coupling matrix elements allow an efficient population of the T1 state. Combined with the crystal protection and conformation effect, the 3,3-conformer crystal shows high phosphorescence efficiency. The unsymmetrical 2,4-conformer conformation with the twisted central benzene ring leads to 1D or 2D crystal growth mode, which has weak crystal protection effect. In addition, the unsymmetrical conformation has a dark GM T1 state that is very close to the T1-S0 CI point, implying an efficient nonradiative T1-S0 quenching. Thus, weak phosphorescence was observed from the unsymmetrical conformation. This study provides an insight for the development of highly emissive phosphorescent materials.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Multidimensional Structure Conformation of Persulfurated Benzene for Highly Efficient Phosphorescence

Baryshnikov

Kuklin

et al. 2020

ACS Appl. Mater. Interfaces

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“…[15,16] The other type of sidechain is a branched triethylene glycol monomethyl ether and octyl group ("B" in Figure 1b), which was chosen from the previous report. [17] Based on the combination of two types of sidechains, we synthesized three PPEs: P1 with alternate A-B, P2 with A-A, and P3 with B-B as shown in Figure 1. The number ratio of triethylene glycol to octyl per repeat unit is 6:2 (P1), 8:0 (P2), and 4:4 (P3).…”

Section: Introductionmentioning

confidence: 99%

Distinct Interfacial Fluorescence in Oil‐in‐Water Emulsions via Exciton Migration of Conjugated Polymers

Koo

Swager

2017

Macromol. Rapid Commun.

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aforementioned types of dyes are the amphiphilic fluorescent probes that are structurally more challenging to synthesize owing to meeting the optimum balance between hydrophobicity and hydrophilicity. [5] Furthermore, the equilibrium of solubility results in the partial amount of dyes residing in water and/or oil phases in addition to interfaces, which could reduce the contrast of fluorescence images between interfaces and backgrounds.Poly(phenylene ethynylene)s (PPEs), fluorescent conjugated polymers, have been extensively investigated as optoelectronic and fluorescent sensory materials. [6][7][8] They possess both large extinction coefficients and high fluorescence quantum yields, resulting from an electronic structure with a direct bandgap [9] as well as rigid butatrienelike excited state structures. [10] The strong brightness makes them suitable materials as fluorescent dyes. One distinct feature of the PPE as a fluorescent probe, compared to other conventional small molecular probes, is that their fluorescence can be switched via exciton migration that can be modulated by their conformations [11] and interpolymer distances. [12,13] We reported [13] that surfactant-type PPEs having low-energy emissive endgroups can display dual fluorescence, which is cyan (backbone) in solution and red (endgroup) in thin films at a single excitation wavelength through energy transfer. In their Langmuir monolayers at the air-water interface, interpolymer distances are controlled, resulting in the ratiometric fluorescence changes. Herein we aim to apply this dual-fluorescence concept to more general amphiphilic colloidal systems. As a proof of concept, we choose oil-in-water emulsions that are stabilized by PPE surfactants. We found that PPEs show cyan fluorescence in water, which switches to red fluorescence in oil-in-water emulsions (Figure 1a) because of the closer interpolymer distance on the confined spherical oil surface, and therefore, the red emission is observed exclusively from the oil-water interface. We envision that this switchable fluorescence between bulk and interface can pave a novel way of high-contrast visualization techniques for many amphiphilic systems found in colloids and bioimaging. Results and DiscussionWe synthesized several perylene end-capped water-soluble PPEs to make oil droplets in water. The perylene is functionalized Fluorescence Commercial dyes are extensively utilized to stain specific phases for the visualization applications in emulsions and bioimaging. In general, dyes emit only one specific fluorescence signal and thus, in order to stain various phases and/or interfaces, one needs to incorporate multiple dyes and carefully consider their compatibility to avoid undesirable interactions with each other and with the components in the system. Herein, surfactant-type, perylene-endcapped fluorescent conjugated polymers that exhibit two different emissions are reported, which are cyan in water and red at oil-water interfaces. The interfacially distinct red emission results from enhanced exciton...

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“…The choice of the amphiphilic PPE is critical to promote the proper organizations. Although energy transfer is efficient in the solid state, aggregation-induced quenching of singlet excitons is notoriously common and can lower the exciton diffusion lengths, giving diminished fluorescence quantum yields. , We previously showed that PPEs having amphiphilic side chains displayed novel behavior wherein the compressed monolayers at the air–water interface formed highly emissive excimers with the increase in relative quantum yields compared to noncompressed states . Therefore, we have targeted this system for further applications by functionalization with low-energy emissive perylene dye end groups (Figure ).…”

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confidence: 99%

Interfacial Pressure/Area Sensing: Dual-Fluorescence of Amphiphilic Conjugated Polymers at Water Interfaces

Koo

Swager

2017

ACS Macro Lett.

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Exciton migration to emissive defects in π-conjugated polymers is a robust signal amplification strategy for optoelectronic sensors. Herein we report endcapped conjugated polymers that show two distinct emissions as a function of interpolymer distances at the air-water and hydrocarbon-water interfaces. Amphiphilic poly(phenylene ethynylene)s (PPEs) endcapped with perylene monoimides display two distinct emission colors (cyan from PPE and red from perylene), the relative intensity of which depends on the surface pressure applied on the Langmuir monolayers. This behavior produces a ratiometric interfacial pressure indicator. Relative quantum yields are maintained at the different surface pressures and hence display no sign of self-quenching of the excitons in an aggregated state. These polymers can be organized at the micelle-water interface in lytropic liquid crystals, thereby paving the way for potential applications of endcapped amphiphilic conjugated polymers in biosensors and bioimaging.

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Highly Emissive Excimers by 2D Compression of Conjugated Polymers

Cited by 10 publications

References 23 publications

Multidimensional Structure Conformation of Persulfurated Benzene for Highly Efficient Phosphorescence

Multidimensional Structure Conformation of Persulfurated Benzene for Highly Efficient Phosphorescence

Distinct Interfacial Fluorescence in Oil‐in‐Water Emulsions via Exciton Migration of Conjugated Polymers

Interfacial Pressure/Area Sensing: Dual-Fluorescence of Amphiphilic Conjugated Polymers at Water Interfaces

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