Resonant Raman-Active Polymer Dot Barcodes for Multiplex Cell Mapping.

Resonance Raman spectroscopy is an efficient tool for multiplex imaging because of the narrow bandwidth of the electronically enhanced vibrational signals. However, Raman signals are often overwhelmed by concurrent fluorescence. In this study, we synthesized a series of truxene-based conjugated Raman probes to show structure-specific Raman fingerprint patterns with a common 532 nm light source. The subsequent polymer dot (Pdot) formation of the Raman probes efficiently suppressed fluorescence via aggregation-induced quenching and improved the dispersion stability of particles without leakage of Raman probes or particle agglomeration for more than 1 year. Additionally, the Raman signal amplified by electronic resonance and increased probe concentration exhibited over 103 times higher relative Raman intensities versus 5-ethynyl-2'-deoxyuridine, enabling successful Raman imaging. Finally, multiplex Raman mapping was demonstrated with a single 532 nm laser using six Raman-active and biocompatible Pdots as barcodes for live cells. Resonant Raman-active Pdots may suggest a simple, robust, and efficient way for multiplex Raman imaging using a standard Raman spectrometer, suggesting the broad applicability of our strategy.

Triplets with a Twist: Ultrafast Intersystem Crossing in a Series of Electron Acceptor Materials Driven by Conformational Disorder.

Control over the populations of singlet and triplet excitons is key to organic semiconductor technologies. In different contexts, triplets can represent an energy loss pathway that must be managed (i.e., solar cells, light-emitting diodes, and lasers) or provide avenues to improve energy conversion (i.e., photon upconversion and multiplication systems). A key consideration in the interplay of singlet and triplet exciton populations in these systems is the rate of intersystem crossing (ISC). In this work, we design, measure, and model a series of new electron acceptor molecules and analyze them using a combination of ultrafast transient absorption and ultrafast broadband photoluminescence spectroscopies. We demonstrate that intramolecular triplet formation occurs within several hundred picoseconds in solution and is accelerated considerably in the solid state. Importantly, ISC occurs with sufficient rapidity to compete with charge formation in modern organic solar cells, implicating triplets in intrinsic exciton loss channels in addition to charge recombination. Density functional theory calculations reveal that ISC occurs in triplet excited states characterized by local deviations from orbital π-symmetry associated with rotationally flexible thiophene rings. In disordered films, structural distortions, therefore, result in significant increases in spin-orbit coupling, enabling rapid ISC. We demonstrate the generality of this proposal in an oligothiophene model system where ISC is symmetry-forbidden and show that conformational disorder introduced by the formation of a solvent glass accelerates ISC, outweighing the lower temperature and increased viscosity. This proposal sheds light on the factors responsible for facile ISC and provides a simple framework for molecular control over spin states.

Elucidating the resonance Raman spectra of psittacofulvins.

Spectroscopic studies into the identification and characterisation of psittacofulvins were performed using resonance Raman spectroscopy. It was confirmed that red colour regions display Raman band wavenumber shifts with excitation wavelength, whereas yellow regions do not. There was, however, one yellow region (Calyptorhynchus banksii) that did display wavenumber shifting with excitation wavelength. The data in Raman band wavenumber shifting is observed may be interpreted as probing sample volumes in which a number of dyes of differing length are present in which comparative resonance Raman signals select out the dyes to differing extents depending on their absorption profile, structurally changes between the ground and excited state and the Raman scattering of particular modes. The observed spectral features suggest the presence of a psittacofulvin with greater conjugation than has been reported previously.

Electroactive Metal Complexes Covalently Attached to Conductive PEDOT Films: A Spectroelectrochemical Study.

The successful covalent attachment, via copper(I)-catalyzed azide alkyne cycloaddition (CuAAC), of alkyne-functionalized nickel(II) and copper(II) macrocyclic complexes onto azide (N3)-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films on ITO-coated glass electrodes is reported. To investigate the surface attachment of the selected metal complexes, which are analogues of the cobalt-based complex previously reported to be a molecular catalyst for hydrogen evolution, first, three different PEDOT films were formed by electropolymerization of pure PEDOT or pure N3-PEDOT, and last, 1:2N3-PEDOT:PEDOT were formed by co-polymerizing a 1:4 mixture of N3-EDOT:EDOT monomers. The successful surface immobilization of the complexes on the latter two azide-functionalized films, by CuAAC, was confirmed by X-ray photoelectron spectroscopy (XPS) and electrochemistry as well as by UV-vis-NIR and resonance Raman spectroelectrochemistry. The ratio between the N3 groups, and hence, the number of surface-attached metal complexes after CuAAC functionalization, in pristine N3-PEDOT versus 1:2N3-PEDOT:PEDOT is expected to be 3:1 and seen to be 2.86:1 with a calculated surface coverage of 3.28 ± 1.04 and 1.15 ± 0.09 nmol/cm2, respectively. The conversion, to the metal complex attached films, was lower for the N3-PEDOT films (Ni 74%, Cu 76%) than for the copolymer 1:2N3-PEDOT:PEDOT films (Ni 83%, Cu 91%) due to the former being more sterically congested. The Raman and UV-vis-NIR results were simulated using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively, and showed good agreement with the experimental data. Importantly, the spectroelectrochemical behavior of both anchored metal complexes is analogous to that of the free metal complexes in solution. This proves that PEDOT films are promising conducting scaffolds for the covalent immobilization of metal complexes, as the existing electrochromic features of the complexes are preserved on immobilization, which is important for applications in electrocatalytic proton and carbon dioxide reduction, optoelectronics, and sensing.

Fluorination Position: A Study of the Optoelectronic Properties of Two Regioisomers Using Spectroscopic and Computational Techniques.

The influence of the fluorination positions on the optical and electronic properties of a pair of donor-acceptor (DA)-based regioisomers is explored. In the regioisomers, the fluorination was varied between the 2 and 3 positions on benzothiadiazole (BTD) acceptor units. Although the structural variation between the regioisomers is small, significant variations in the electronic properties of the two compounds were observed. These were observed most markedly in the excited-state properties with a 15 nm (280-390 cm-1) red shift of the emission between the regioisomers. The combination of resonance Raman spectroscopy (RRS) and density functional theory (DFT) calculations was used to probe the possible causes of the observed variations. The analysis suggested a F···S through-space interaction as being responsible for tuning both the electronic properties and rigidity of the compounds. Shifting the fluorine atoms shifted the location of the F···S interaction, changing which part of the molecule was locked down, and showed a variation in the overall rigidity of the molecule. In this series, the influence could be varied between the core and periphery. This study adds to a growing body of work demonstrating the effectiveness of selective fluorination in tailoring the properties of organic molecules.

Long-lived MLCT states for Ru(ii) complexes of ferrocene-appended 2,2'-bipyridines.

In this study, we present two ruthenium(ii) diimine complexes appended with ferrocene which show metal to ligand charge transfer 3MLCT emission lifetimes around 630 ns. We also present a similar complex with two ferrocene units which has decreased emission. These complexes have been studied by electrochemical, electronic absorption, and Raman, resonance Raman and transient resonance Raman means, coupled with density functional theoretical approaches. For these systems, the optical spectra are dominated by a low energy ruthenium(ii) MLCT transition; which can be modulated by the presence of pendant ferrocene units and the extent of conjugation of the ferrocenyl bipyridine backbone. Tuning of the lowest energy transition in terms of intensity (4 to 18 × 10-3 M-1 cm-1) and energy (535 to 563 nm) was achieved by these means.

Frequency dispersion reveals chromophore diversity and colour-tuning mechanism in parrot feathers.

Variation in animal coloration is often viewed as the result of chemically distinct pigments conferring different hues. The role of molecular environment on hue tends to be overlooked as analyses are mostly performed on free pigments extracted from the integument. Here we analysed psittacofulvin pigments within parrot feathers to explore whether the in situ organization of pigments may have an effect on hue. Resonance Raman spectra from a red region of a yellow-naped amazon Amazona auropalliata tail feather show frequency dispersion, a phenomenon that is related to the presence of a range of molecular conformations (and multiple chromophores) in the pigment, whereas spectra from a yellow region on the same feather do not show the same evidence for multiple chromophores. Our findings are consistent with non-isomeric psittacofulvin pigments behaving as a single chromophore in yellow feather barbs, which implies that psittacofulvins are dispersed into a structurally disordered mixture in yellow feathers compared with red feathers. Frequency dispersion in red barbs may instead indicate that pigments are structurally organized through molecule-molecule interactions. Major differences in the hues of parrot feathers are thus associated with differences in the organization of pigments within feathers.