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Excitonic luminescence of hemiporphyrazines


Huber, Sabrina M; Seyfried, Martin S; Linden, Anthony; Luedtke, Nathan W (2012). Excitonic luminescence of hemiporphyrazines. Inorganic chemistry, 51(13): 7032-7038.

Abstract

Metal-free hemiporphyrazine (HpH2) is a notoriously insoluble material possessing interesting photophysical properties. Here we report the synthesis, structure, and photophysical properties of an octahedral zinc trans-ditriflate hemiporphyrazine complex “HpH2Zn(OTf)2” that contains a neutral hemiporphyrazine ligand. The photophysical properties of hemiporphyrazine are largely unaffected by introduction of zinc(II) triflate, but a dramatic increase in solubility is observed. HpH2Zn(OTf)2 therefore provides a convenient model system to evaluate the impact of aggregation on the photophysical properties of hemiporphyrazine. Soluble aggregates and crystalline materials containing planar hemiporphyrazines exhibit relatively strong absorbance of visible light (450–600 nm) and red luminescence (600–700 nm). Hemiporphyrazine monohydrate (HpH2·H2O), in contrast, has a nonplanar “saddle-shaped” conformation that exhibits very little absorbance of visible light in solution or in the solid state. Upon photoexcitation at 380 nm, HpH2Zn(OTf)2 and HpH2 exhibit multiwavelength emissions centered at 450 and 650 nm. Emissions at 450 nm are highly anisotropic, while emissions at 650 nm are fully depolarized with respect to a plane-polarized excitation source. Taken together, our results suggest that excitonic coupling of aggregated and crystalline hemiporphyrazines results in increased absorbance and emission of visible light from S0 ↔ S1 transitions that are usually symmetry forbidden in isolated species. In contrast to previously proposed theories involving excited-state intramolecular proton transfer, we propose that the multiple-wavelength luminescent emissions of HpH2Zn(OTf)2 and HpH2 are due to emissive S1 and S2 states in aggregated and crystalline hemiporphyrazines. These results may provide a better understanding of the nonlinear optical properties of these materials in solution and in the solid state.

Abstract

Metal-free hemiporphyrazine (HpH2) is a notoriously insoluble material possessing interesting photophysical properties. Here we report the synthesis, structure, and photophysical properties of an octahedral zinc trans-ditriflate hemiporphyrazine complex “HpH2Zn(OTf)2” that contains a neutral hemiporphyrazine ligand. The photophysical properties of hemiporphyrazine are largely unaffected by introduction of zinc(II) triflate, but a dramatic increase in solubility is observed. HpH2Zn(OTf)2 therefore provides a convenient model system to evaluate the impact of aggregation on the photophysical properties of hemiporphyrazine. Soluble aggregates and crystalline materials containing planar hemiporphyrazines exhibit relatively strong absorbance of visible light (450–600 nm) and red luminescence (600–700 nm). Hemiporphyrazine monohydrate (HpH2·H2O), in contrast, has a nonplanar “saddle-shaped” conformation that exhibits very little absorbance of visible light in solution or in the solid state. Upon photoexcitation at 380 nm, HpH2Zn(OTf)2 and HpH2 exhibit multiwavelength emissions centered at 450 and 650 nm. Emissions at 450 nm are highly anisotropic, while emissions at 650 nm are fully depolarized with respect to a plane-polarized excitation source. Taken together, our results suggest that excitonic coupling of aggregated and crystalline hemiporphyrazines results in increased absorbance and emission of visible light from S0 ↔ S1 transitions that are usually symmetry forbidden in isolated species. In contrast to previously proposed theories involving excited-state intramolecular proton transfer, we propose that the multiple-wavelength luminescent emissions of HpH2Zn(OTf)2 and HpH2 are due to emissive S1 and S2 states in aggregated and crystalline hemiporphyrazines. These results may provide a better understanding of the nonlinear optical properties of these materials in solution and in the solid state.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:15 June 2012
Deposited On:05 Feb 2013 13:12
Last Modified:05 Apr 2016 16:23
Publisher:American Chemical Society
ISSN:0020-1669
Additional Information:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see dx.coi.org/10.1021/ic2017566.
Publisher DOI:https://doi.org/10.1021/ic2017566
PubMed ID:22702723

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