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Structure-Directed Exciton Dynamics in Templated Molecular Nanorings.

Gong JQ, Parkinson P, Kondratuk DV, Gil-Ramírez G, Anderson HL, Herz LM - J Phys Chem C Nanomater Interfaces (2015)

Bottom Line: Recent advances in Vernier templating now allow large shape-persistent fully conjugated porphyrin nanorings to be synthesized, exhibiting unique electronic properties.Low photoluminescence anisotropy values are found to occur within the first few hundred femtoseconds after pulsed excitation, suggesting ultrafast delocalization of excitons across the nanoring structures.Molecular dynamics simulations show that further polarization memory loss is caused by out-of-plane distortions associated with twisting and bending of the templated nanoring topologies.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.

ABSTRACT

Conjugated polymers with cyclic structures are interesting because their symmetry leads to unique electronic properties. Recent advances in Vernier templating now allow large shape-persistent fully conjugated porphyrin nanorings to be synthesized, exhibiting unique electronic properties. We examine the impact of different conformations on exciton delocalization and emission depolarization in a range of different porphyrin nanoring topologies with comparable spatial extent. Low photoluminescence anisotropy values are found to occur within the first few hundred femtoseconds after pulsed excitation, suggesting ultrafast delocalization of excitons across the nanoring structures. Molecular dynamics simulations show that further polarization memory loss is caused by out-of-plane distortions associated with twisting and bending of the templated nanoring topologies.

No MeSH data available.


Related in: MedlinePlus

Normalizedsteady-state absorption (blue lines) and time-integratedphotoluminescence (green lines) spectra at 295 K for (a) c-P12 in toluene/1% pyridine and (b) c-P12·(T6)2 in toluene solution. The emission spectra were recorded after excitationat 520 nm (into the Soret band). The Qx and Qy transitions are indicated by red arrows.
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fig2: Normalizedsteady-state absorption (blue lines) and time-integratedphotoluminescence (green lines) spectra at 295 K for (a) c-P12 in toluene/1% pyridine and (b) c-P12·(T6)2 in toluene solution. The emission spectra were recorded after excitationat 520 nm (into the Soret band). The Qx and Qy transitions are indicated by red arrows.

Mentions: In order to gain basicinsight about the photophysical and electronic properties of the nanorings,steady state absorption and emission spectroscopy was performed. Theresulting spectra for c-P12 and c-P12·(T6)2 are compared in Figure 2; spectra forfurther structures are provided in the SI. Zinc porphyrin monomers exhibit a strong S0 →S2 transition at ∼400 nm (Soret band) and a weakerS0 → S1 transition at ∼550 nm(Q-band).35 For the nanorings, π-conjugationextends through the butadiyne bridges, lifting the degeneracy in boththe lowest-energy Q band and Soret band of the porphyrinmonomers. Transitions polarized parallel (Qx) and perpendicular (Qy) to the acetylenic backbone can therefore be observed(see Figure 2). When the nanorings bind tothe templates, Qx isobserved to be red-shifted with respect to the Soret band, while Qy shows no considerable change.In addition, a significant sharpening of features in both emissionand absorption spectra can be observed for the templated complexes.Templates bring rigidity to the system; the molecules are less proneto interporphyrin torsional motions and the molecular backbone maybe planarized,18 resulting in the observedred shift of Qx. Thefour templated nanorings hence exhibit similar spectral features (seealso further spectra in the SI).


Structure-Directed Exciton Dynamics in Templated Molecular Nanorings.

Gong JQ, Parkinson P, Kondratuk DV, Gil-Ramírez G, Anderson HL, Herz LM - J Phys Chem C Nanomater Interfaces (2015)

Normalizedsteady-state absorption (blue lines) and time-integratedphotoluminescence (green lines) spectra at 295 K for (a) c-P12 in toluene/1% pyridine and (b) c-P12·(T6)2 in toluene solution. The emission spectra were recorded after excitationat 520 nm (into the Soret band). The Qx and Qy transitions are indicated by red arrows.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4418736&req=5

fig2: Normalizedsteady-state absorption (blue lines) and time-integratedphotoluminescence (green lines) spectra at 295 K for (a) c-P12 in toluene/1% pyridine and (b) c-P12·(T6)2 in toluene solution. The emission spectra were recorded after excitationat 520 nm (into the Soret band). The Qx and Qy transitions are indicated by red arrows.
Mentions: In order to gain basicinsight about the photophysical and electronic properties of the nanorings,steady state absorption and emission spectroscopy was performed. Theresulting spectra for c-P12 and c-P12·(T6)2 are compared in Figure 2; spectra forfurther structures are provided in the SI. Zinc porphyrin monomers exhibit a strong S0 →S2 transition at ∼400 nm (Soret band) and a weakerS0 → S1 transition at ∼550 nm(Q-band).35 For the nanorings, π-conjugationextends through the butadiyne bridges, lifting the degeneracy in boththe lowest-energy Q band and Soret band of the porphyrinmonomers. Transitions polarized parallel (Qx) and perpendicular (Qy) to the acetylenic backbone can therefore be observed(see Figure 2). When the nanorings bind tothe templates, Qx isobserved to be red-shifted with respect to the Soret band, while Qy shows no considerable change.In addition, a significant sharpening of features in both emissionand absorption spectra can be observed for the templated complexes.Templates bring rigidity to the system; the molecules are less proneto interporphyrin torsional motions and the molecular backbone maybe planarized,18 resulting in the observedred shift of Qx. Thefour templated nanorings hence exhibit similar spectral features (seealso further spectra in the SI).

Bottom Line: Recent advances in Vernier templating now allow large shape-persistent fully conjugated porphyrin nanorings to be synthesized, exhibiting unique electronic properties.Low photoluminescence anisotropy values are found to occur within the first few hundred femtoseconds after pulsed excitation, suggesting ultrafast delocalization of excitons across the nanoring structures.Molecular dynamics simulations show that further polarization memory loss is caused by out-of-plane distortions associated with twisting and bending of the templated nanoring topologies.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.

ABSTRACT

Conjugated polymers with cyclic structures are interesting because their symmetry leads to unique electronic properties. Recent advances in Vernier templating now allow large shape-persistent fully conjugated porphyrin nanorings to be synthesized, exhibiting unique electronic properties. We examine the impact of different conformations on exciton delocalization and emission depolarization in a range of different porphyrin nanoring topologies with comparable spatial extent. Low photoluminescence anisotropy values are found to occur within the first few hundred femtoseconds after pulsed excitation, suggesting ultrafast delocalization of excitons across the nanoring structures. Molecular dynamics simulations show that further polarization memory loss is caused by out-of-plane distortions associated with twisting and bending of the templated nanoring topologies.

No MeSH data available.


Related in: MedlinePlus