Suppressing Solid-State Quenching in Red-Emitting Conjugated Polymers

Abstract

Conjugated polymers with intense solid-state emission are vital for the development of next-generation optoelectronic devices. In particular, it remains extremely challenging to construct π-conjugated systems which emit in the red region of the electromagnetic spectrum and also retain their optical properties and intense photoluminescence in the solid state. In this article we report the synthesis and characterization of three novel diketopyrrolopyrrole-based conjugated polymers, with systematic variation of the covalent encapsulation density. Through control of the distance and density of encapsulation, our red-emitting polymers demonstrate that aggregation caused quenching can be mostly eliminated, culminating in the most efficient solid-state photoluminescence from red conjugated polymers to date.

Molecular Encapsulation of Naphthalene Diimide (NDI) Based π‐Conjugated Polymers: A Tool for Understanding Photoluminescence

“…It is commonly assumed and observed that conjugated polymers undergo substantial photoluminescence quenching on going from solution to the solid state.O ur combined morphological and photophysical results show the surprising result that i) the extremely well-known polymer P(NDI-2OD-T) undergoes strong aggregation induced enhanced emission and ii)t his phenomenon originates from the interchain packing.W e( and others) have previously shown that molecular encapsulation allows ap olymer to retain, to some extent, solution properties when in the solid state. [13,14] In this work, we find the same concept applies to P(E-NDI-T) as both the absorption and emission shapes,yields and lifetimes are almost identical. However,incontrast to almost all other reported conjugated polymers,t he emissivity of the nonencapsulated derivative increases in the solid state (as opposed to decreasing), resulting in arelatively high emission PLQY for this wavelength region.…”

“…This trend is consistent with previous studies on encapsulated conjugated materials. [13,14,43] Similarly,t he photoluminescence (PL) of the three polymers in solution is almost identical, with a l max at % 636 nm. This suggests that, in solution, the emission originates from isolated chains.I nt hin film, on the other hand, the spectra are again progressively red-shifted according to the "exposure" of the polymer chains to one another.…”

“…[11,12] Hence,i ncreasing the PLQY of narrow band gap conjugated polymers is essential for next generation OPV,aswell as being appealing for light emitting diodes and biological imaging.I ti sc ommonly assumed that the close packing of conjugated polymers results in the creation of additional non-radiative decay pathways.T herefore,t he most promising strategy to increase the solid-state PLQY of conjugated polymers is to molecularly isolate the chains either through covalent or non-covalent encapsulation. [13][14][15][16][17][18][19][20][21] Polymer dilution in ahost matrix can also be used to increase PLQY but this cannot suppress intramolecular interactions,oreven intermolecular in some cases. [22] Herein, we report the synthesis and characterization of an ovel encapsulated conjugated NDI polymer and report the resulting effect of molecular encapsulation on its optical properties.…”

“…Therefore, the most promising strategy to increase the solid-state PLQY of conjugated polymers is to molecularly isolate the chains either through covalent or non-covalent encapsulation. [13][14][15][16][17][18][19][20][21] Polymer dilution in a host matrix can also be used to increase PLQY but this cannot suppress intramolecular interactions, or even intermolecular in some cases. [22] Herein, we report the synthesis and characterization of a novel encapsulated conjugated NDI polymer and report the resulting effect of molecular encapsulation on its optical properties.…”

Suppressing aggregation induced quenching in anthracene based conjugated polymers

“…Work from our group and others has shown that covalent alkylene encapsulation can increase molecular rigidity and suppress AIQ to afford highly luminescent materials that retain much of their desirable solution photophysics in the solid state. [32][33][34][35][36] Kobayashi and coworkers have also proven the viability of such a tactic for preserving the photophysical performance of DPA in powder and pristine films. 37 However, covalent encapsulation has never been implemented in anthracene based polymers despite its clear potential to improve their photophysical performance.…”