Circularly Polarized Luminescence Spectroscopy Research Articles

Fundamentals, Advances, and Artifacts in Circularly Polarized Luminescence (CPL) Spectroscopy.

Objects are chiral when they cannot be superimposed with their mirror image. Materials can emit chiral light with an excess of right- or left-handed circular polarization. This circularly polarized luminescence (CPL) is key to promising future applications, such as highly efficient displays, holography, sensing, enantiospecific discrimination, synthesis of drugs, quantum computing, and cryptography. Here, a practical guide to CPL spectroscopy is provided. First, the fundamentals of the technique are laid out and a detailed account of recent experimental advances to achieve highly sensitive and accurate measurements is given, including all corrections required to obtain reliable results. Then the most common artifacts and pitfalls are discussed, especially for the study of thin films, for example, based on molecules, polymers, or halide perovskites, as opposed to dilute solutions of emitters. To facilitate the adoption by others, custom operating software is made publicly available, equipping the reader with the tools needed for successful and accurate CPL determination.

Spatiotemporal Mapping of Efficient Chiral Induction by Helicene-Type Additives in Copolymer Thin Films.

We observed efficient induction of chirality in polyfluorene copolymer thin films by mixing with helicene‐type chiral additives based on the dibenzo[c,h]acridine motif. Images obtained from circular dichroism (CD) and circularly polarized luminescence (CPL) microscopy provide information about the chiral arrangements in the thin films with diffraction‐limited resolution. The CD signal shows a characteristic dependence on the film thickness, which supports a supramolecular origin of the strong chiral response of the copolymer. In particular, we demonstrate the discrimination between films of opposite chirality based on their ultrafast transient chiral response through the use of femtosecond broadband CD spectroscopy and a newly developed setup for transient CPL spectroscopy with 28 ps time resolution. A systematic variation of the enantiomeric excess of the chiral additive shows that the “Sergeants and Soldiers” concept and “Majority Rules” are not obeyed.

Front Cover: Mirror‐Image Cofacial Coronene Dimers Characterized by CD and CPL Spectroscopy: A Twisted Bilayer Nanographene (ChemPhotoChem 11/2021)

The Front Cover shows Mt. Fuji, the highest mountain in Japan, reflecting off the water surface in a beautiful symmetrical form. On this image, we superimposed the mirror-image circularly polarized luminescence (CPL) spectra of the 1,8-naphthylene-linked face-to-face coronene dimer reported in this study. More information can be found in the Communication by Hiroko Yamada, Naoki Aratani and co-workers.

Mirror‐Image Cofacial Coronene Dimers Characterized by CD and CPL Spectroscopy: A Twisted Bilayer Nanographene

AbstractBilayer graphene (BLG), which changes its electronic properties significantly depending on the interplanar distance and rotation angle, is a hot research topic. We successfully synthesized discrete BLG models by bridging two coronenes with a 1,8‐naphthalene linkage (C2). Owing to the large rotational energy, the syn‐ and anti‐atropisomers of C2 could be isolated. X‐ray crystallographic analysis revealed that the syn‐form (C2S) is an AB stacking type and the anti‐form (C2A) is a chiral twisted bilayer graphene (TBG) type. Therefore, the anti‐form of C2 was optically resolved and characterized by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The Cotton effect was observed in the CD spectra at the longest absorption wavelength, and the corresponding bisignate CPL spectra were observed. The dissymmetry factors |glum| of C2A were found to be 2.0×10−3 at 435 nm and 1.2×10−3 at 450 nm.

Temperature-Dependent Circularly Polarized Luminescence Measurement Using KBr Pellet Method.

Circularly polarized luminescence (CPL) spectroscopy measures the difference in luminescence intensity between left- and right-circularly polarized light, and is often used to analyze the structure of chiral molecules in their excited state. Recently, it has found an increasing range of applications in the analysis of molecules that emit circularly polarized light and can be employed in 3D displays. Thus, the number of articles focusing on CPL spectroscopy has increased dramatically. However, since the luminescence dissymmetry factor (glum) for organic compounds is generally <|0.01|, CPL spectrometers must offer high sensitivity and produce spectra that are artifact-free for chiral molecules. Until now, the principal targets of CPL measurements have been solution samples. However, for practical device applications, it is also necessary to be able to measure the CPL spectra of solid-state samples. In addition, since electronic devices often operate at high temperatures, it is important to evaluate the thermal dependence of the CPL characteristics. Moreover, in the measurement of solid-state samples, the degree of anisotropy of the samples must be evaluated, because a large degree of anisotropy can cause artifacts. Therefore, we describe methods to evaluate the degree of anisotropy of solid-state samples and their high-temperature applications.

Circularly polarized luminescence spectroscopy reveals low-energy excited states and dynamic localization of vibronic transitions in CP43

Circularly polarized luminescence (CPL) spectroscopy is an established but relatively little-used technique that monitors the chirality of an emission. When applied to photosynthetic pigment assemblies, we find that CPL provides sensitive and detailed information on low-energy exciton states, reflecting the interactions, site energies and geometries of interacting pigments. CPL is the emission analog of circular dichroism (CD) and thus spectra explore the optical activity only of fluorescent states of the pigment-protein complex and consequently the nature of the lowest-energy excited states (trap states), whose study is a critical area of photosynthesis research. In this work, we develop the new approach of temperature-dependent CPL spectroscopy, over the 2–120K temperature range, and apply it to the CP43 proximal antenna protein of photosystem II. Our results confirm strong excitonic interactions for at least one of the two well-established emitting states of CP43 named “A” and “B”. Previous structure-based models of CP43 spectra are evaluated in the light of the new CPL data. Our analysis supports the assignments of Shibata et al. [Shibata et al. J. Am. Chem. Soc. 135 (2013) 6903–6914], particularly for the highly-delocalized B-state. This state dominates CPL spectra and is attributed predominantly to chlorophyll a's labeled Chl 634 and Chl 636 (alternatively labeled Chl 43 and 45 by Shibata et al.). The absence of any CPL intensity in intramolecular vibrational sidebands associated with the delocalized “B” excited state is attributed to the dynamic localization of intramolecular vibronic transitions.

Chiroptical Spectra of a Series of Tetrakis((+)-3-heptafluorobutylyrylcamphorato)lanthanide(III) with an Encapsulated Alkali Metal Ion: Circularly Polarized Luminescence and Absolute Chiral Structures for the Eu(III) and Sm(III) Complexes

The luminescence and circularly polarized luminescence (CPL) spectra of M(I)[Eu((+)-hfbc)(4)] show a similar behavior to the exciton CD in the intraligand π-π* transitions when the alkali metal ions and solvents are manipulated. There is a difference in susceptibility in solvation toward the alkali metal ions but not toward the Eu(III) ion, as in the case of axially symmetric DOTA-type compounds. The remarkable CPL in the 4f-4f transitions provide much more information on the stereospecific formation of chiral Eu(III) complexes, since CPL spectroscopy is limited to luminescent species and reflects selectively toward helicity of the local structural environment around the lanthanide(III). While in comparison, exciton CD reveals the chiral structural information from the helical arrangement of the four bladed chelates. Of special importance, the observation of the highest CPL activities measured to date for lanthanide(III)-containing compounds (i.e., Eu and Sm) in solution supports the theory that the chirality of lanthanide(III) in the excited state corresponds to that in the ground state, which was derived from the exciton CD.

Application of Circularly Polarized Luminescence Spectroscopy to Tb(III) and Eu(III) Complexes of Transferrins

Circularly polarized luminescence (CPL) and total luminescence of Tb(III) and Eu(III) as substitutional replacements for iron in a series of Fe binding transferrins are reported. The measurement of the total emission intensity is a direct measure of binding of the lanthanide ions and illustrates that approximately 2 equiv of Tb(III) and Eu(III) is bound to these proteins. In agreement with previous work, circularly polarized luminescence from Tb(III) bound to the transferrins is quite large. Additional measurements show that the net CPL displays no dependence on concentration of the metal ion and shows little variation between the two binding sites. CPL from lactoferrin is very similar to serum transferrin, however, ovotransferrin shows differences in line shape and magnitude. These results are discussed in the context of the previously published crystal structure of the binding sites of the three proteins.

Circularly Polarized Luminescence Studies of Chiral Lanthanide Complexes

Abstract The utility of circularly polarized luminescence (CPL) spectroscopy in the study of lanthanide ion coordination chemistry has been described. A variety of optically active Tb(III) and Eu(III) compounds have been considered, containing chiral carboxylic acids, chiral amino acids, chiral aminopolycarboxylic acids, achiral β-diketones and chiral substrates, and chiral β-diketones and achiral substrates. In addition, studies of the Pfeiffer effect in lanthanide compounds have also been discussed. CPL spectroscopy has been found to be the chiroptical technique of choice for lanthanide compounds, and a considerable amount of structural and stereochemical information has been obtained from these investigations.

ChemInform Abstract: Circularly Polarized Luminescence Spectroscopy of Mixed‐Ligand Complexes of Europium(III) with 2,6‐Pyridine‐dicarboxylic Acid and L‐Malic Acid.

ChemInform Abstract: Circularly Polarized Luminescence Spectroscopy of Mixed‐Ligand Complexes of Europium(III) with 2,6‐Pyridine‐dicarboxylic Acid and L‐Malic Acid.

Optical Artifacts in Circularly Polarized Luminescence Spectroscopy

The source of optical artifacts in circularly polarized luminescence is examined by application of the method of Mueller matrices. Expressions for the circularly polarized luminescence intensity are developed that illustrate that the source of the artifact in most cases is due to the small inherent birefringence in the photoelastic modulator employed in the experimental measurement. Experimental results are presented that are consistent with this conclusion.

ChemInform Abstract: A STRUCTURAL STUDY OF TRIS(β‐DIKETONATE)EUROPIUM(III) COMPLEXES IN SOLUTION USING MAGNETIC CIRCULARLY POLARIZED LUMINESCENCE SPECTROSCOPY

Chemischer InformationsdienstVolume 12, Issue 16 Physical Organic Chemistry ChemInform Abstract: A STRUCTURAL STUDY OF TRIS(β-DIKETONATE)EUROPIUM(III) COMPLEXES IN SOLUTION USING MAGNETIC CIRCULARLY POLARIZED LUMINESCENCE SPECTROSCOPY F. S. RICHARDSON, F. S. RICHARDSONSearch for more papers by this authorH. G. BRITTAIN, H. G. BRITTAINSearch for more papers by this author F. S. RICHARDSON, F. S. RICHARDSONSearch for more papers by this authorH. G. BRITTAIN, H. G. BRITTAINSearch for more papers by this author First published: April 21, 1981 https://doi.org/10.1002/chin.198116050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume12, Issue16April 21, 1981 RelatedInformation