Evidence for excimer photoexcitations in an ordered<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>π</mml:mi></mml:mrow></mml:math>-conjugated polymer film

Aryanpour, Karan; Sheng, Chuanxiang; Olejnik, Ella; Pandit, Bill; Psiachos, D.; Mazumdar, S.; Vardeny, Z. Valy

doi:10.1103/physrevb.83.155124

Cited by 28 publications

(50 citation statements)

References 25 publications

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“…Recently our joint theory-experiment work reported pressure-dependent transient picosecond and continuous-wave photomodulation studies of disordered and ordered films of MEH-PPV. Photoinduced absorption bands of intrachain excitons and polarons in the disordered film exhibited weak pressure dependence [41]. In contrast, the ordered film exhibited two additional transient PA bands in the mid infrared that blue-shift dramatically with pressure.…”

Section: Transient Photomodulation Spectroscopy Of Pristine Meh-ppv Fmentioning

confidence: 98%

“…The branching of intrachain and interchain photoexcitations occurs instantaneously in many systems [39,40]. This topic has been the focus of interest for more than two decades [41]. Here we discuss some intrachain and interchain excitations that are neutral and charged.…”

Section: Optical Transitions Of Photoexcitations In Pristine Polymersmentioning

confidence: 99%

“…In contrast, the ordered film exhibited two additional transient PA bands in the mid infrared that dramatically blue-shifted with pressure. Based on high-order configuration interaction calculations, we ascribed the PA bands in the ordered film to excimers [41]. The excimer is a quantum-mechanical superposition of the delocalized neutral exciton and the ionic polaron pair that is obtained in the presence of significant interchain electron hopping.…”

Section: Polaron Pairsmentioning

confidence: 99%

“…In contrast, the ordered film exhibited two additional transient PA bands in the mid infrared that blue-shift dramatically with pressure. Based on high-order configuration interaction calculations, we ascribed the PA bands in the ordered film to excimers [41].…”

Section: Transient Photomodulation Spectroscopy Of Pristine Meh-ppv Fmentioning

confidence: 99%

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Optical Studies of Photoexcitations in Polymer/Fullerene Blends for Organic Photovoltaic Applications

Sheng

Vardeny

2015

Topics in Applied Physics

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We used a variety of optical probe techniques including broadband femtosecond transient and continuous wave (cw) photomodulation spectroscopies and electroabsorption for studying the photophysics in two typical π-conjugated polymers, namely regio-regular poly (3-hexyl thiophene) (RR-P3HT) with selforganized π-stacked two-dimensional lamellae, and 2-methoxy-5-(2′-ethylhexyloxy) poly(p-para-phenylene-vinylene) (MEH-PPV) with amorphous nanomorphology; both polymers in pristine and blend with fullerene molecules. In the pristine forms we identified singlet excitons as the primary photoexcitations, having typical photoinduced absorption (PA) band that is correlated with stimulated emission. In contrast, in polymer/fullerene blends the photogenerated excitons quickly decay giving rise to a novel photoexcitation species, and the stimulated emission is absent. For the blends we provide strong evidence for the existence of charge transfer complex (CTC) manifold that is formed inside the optical gap of the polymer and fullerene constituents, which is clearly revealed in the electro-absorption spectrum. Because the lowest energy CTC lies below the optical gap then it is possible to directly generate polarons in the blends without involving intrachain excitons in the polymer phase, when using below gap pump excitation. When using excellent quality materials we present evidence that the CTC states are populated in RR-P3HT/fullerene blend within 20 ps following exciton photogeneration in the polymer chains; but no charge polarons are generated on their expense up to *2 ns. Interestingly the CTC states are photogenerated much faster in D-A blends having smaller domain size such as in regio-random P3HT/PCBM and MEH-PPV/C 60 ; however the CTCs do not easily dissociate in these blends because of the large binding energy. Our findings indicate that the CTC state and film morphology play a

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Section: Transient Photomodulation Spectroscopy Of Pristine Meh-ppv Fmentioning

confidence: 98%

Section: Optical Transitions Of Photoexcitations In Pristine Polymersmentioning

confidence: 99%

Section: Polaron Pairsmentioning

confidence: 99%

Section: Transient Photomodulation Spectroscopy Of Pristine Meh-ppv Fmentioning

confidence: 99%

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Optical Studies of Photoexcitations in Polymer/Fullerene Blends for Organic Photovoltaic Applications

Sheng

Vardeny

2015

Topics in Applied Physics

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“…Excimers in turn refers to interchain species that interact exclusively in the excited state, resulting in changes in the fluorescence, but not the absorption spectra. 40 Insight on the CPE chain conformation can be gained by comparing the observed spectral and NP size trends (Table 1). Increasing the water content from 0.5% to 15% v/v leads to smaller NPs with blue-shifted fluorescence.…”

Section: Effect Of Water Content In H 2 O/thf and H 2 O/mecn Mixturesmentioning

confidence: 99%

Heterogeneous Charge Mobility in Individual Conjugated Polyelectrolyte Nanoparticles Revealed by Two-Color Single Particle Spectroelectrochemistry Studies

2015

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The optoelectronic properties of conjugated polymers and conjugated polyelectrolytes (CPEs) depend on their chain conformation and packing. Correlations between emission color, charge mobility and extent of aggregation in these materials have been previously established from bulk studies. Here we describe the preparation of stable nanoparticle suspensions of the CPE poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene (MPS-PPV) where changes in the solvent composition enable tuning their emission spectra and quantum yield. Employing a newly developed color-sensitive single-molecule spectroelectrochemistry (SMS-EC) technique, the effect of chain conformation on the optoelectronic properties of MPS-PPV nanoparticles is monitored at the single particle level. Within a single particle the photoluminescence and redox response is chromatically-correlated reflecting on the differing contributions that coiled and deaggregated vs. extended and packed segments have on their optoelectronic properties. We also observe a heterogeneous response among nanoparticles to externally applied electrochemical potentials which further correlates with their emission color (chain packing). We rationalize our observations on differential charge injection, energy and charge transport and ion migration as a consequence of chain conformation, packing effects, and the presence of electrochemically reducible quenching sites. Our work provides a way to unravel the intrinsic heterogeneity of CPE materials to better understand the relationship between chain conformation and optoelectronic properties.

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Light Harvesting and Photocurrent Generation in a Conjugated Polymer Nanoparticle–Reduced Graphene Oxide Composite

et al. 2017

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Polymer-graphene nanocomposites are promising candidates for light harvesting applications such as photocatalysis and photovoltaics, where significant charge separation occurs due to photoinduced electron transfer. Much attention has been paid to using reduced graphene oxide (r-GO) as template for anchoring various nanomaterials due to its efficient electron accepting and transport properties. Here, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) nanoparticles are prepared from MEH-PPV polymer and the change in photophysical properties upon formation of polymer nanoparticles (PNPs) from the molecular state are investigated by using steady-state and time-resolved spectroscopy. Nanocomposites are constructed by adding hexadecylamine-functionalized positively charged MEH-PPV PNPs to a solution of negatively charged r-GO. Steady-state and time-resolved spectroscopy are also used to study the electronic interactions between PNPs and r-GO. Ultrafast femtosecond up-conversion and transient absorption spectroscopy unequivocally confirms the electron transfer process from the excited state of MEH-PPV PNPs to r-GO at the interface of the nanocomposite. Analysis reveals that the charge separation time is found to be pulse-width-limited (<100 fs). Due to charge separation in these nanocomposites, an increase (2.6 fold) of photocurrent under visible light illumination is obtained. The fundamental understanding of the charge transfer dynamics affords new opportunities to design efficient light-harvesting systems based on inorganic-organic hybrids.

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Evidence for excimer photoexcitations in an orderedπ-conjugated polymer film

Cited by 28 publications

References 25 publications

Optical Studies of Photoexcitations in Polymer/Fullerene Blends for Organic Photovoltaic Applications

Optical Studies of Photoexcitations in Polymer/Fullerene Blends for Organic Photovoltaic Applications

Heterogeneous Charge Mobility in Individual Conjugated Polyelectrolyte Nanoparticles Revealed by Two-Color Single Particle Spectroelectrochemistry Studies

Light Harvesting and Photocurrent Generation in a Conjugated Polymer Nanoparticle–Reduced Graphene Oxide Composite

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