Photoexcited triplet states of twisted acenes investigated by Electron Paramagnetic Resonance

Twisting of the acene backbone out of planarity in twisted acenes leads to a variation in their optical and electronic properties. The effect of increasing twist angles on the properties of the photoexcited triplet states of a series of anthracene-based helically tethered twisted acenes is investigated here by Electron Paramagnetic Resonance (EPR) spectroscopy. Increasing signal intensities with increasing twist angles indicate increased intersystem crossing efficiencies for the twisted molecules compared to the untethered reference compound. Variations in the electron spin polarisation observed in the transient EPR spectra, in particular for the compound with the shortest tether, imply changes in the sublevel population kinetics depending on molecular geometry. Changes in the zero-field splitting parameters and in the proton hyperfine couplings for compounds with short tethers and therefore higher twist angles point towards a slight redistribution of the spin density compared to the parent compound. The experimental results can be explained by considering both an increase in twist angle and a related decrease in the dihedral angle between the phenyl side groups and the acene core. The observation of a clear excitation-wavelength dependence suggests preferential excitation of different molecular conformations, with conformers characterised by higher twist angles selected at higher wavelengths

Raman and ROA analyses of twisted anthracenes: connecting vibrational and electronic/photonic structures

In this article the Raman and Raman Optical Activity (ROA) spectra of a series of enantiomeric twisted anthracenes are presented. The evolution of their vibrational spectra is understood in the context of the variation of p-electron delocalization as a result of the twisting imparted by the belt structure and in terms of the modulation of the resonance Raman/ROA effects which are photonic properties also tuned by anthracene twisting. The Raman/ROA vibrational spectra are simulated by several theoretical approaches to account for their vibrational and electronic properties including the theoretical evaluation of resonance effects. We furthermore incorporate a vibrational and ROA activity dissection analysis as provided in the Pyvib2 program valid to establish correlations among vibrational modes of different molecules with different electronic structures and equivalent vibrational dynamics. This paper is one of the very first attempts to use ROA spectroscopy in p-conjugated molecules with twisted and helical morphologies that contrast with the well-known cases of ROA studies of chiral helicenes in which the impact of p-electron delocalization in the electronic/photonic/vibrational (Raman/ROA) spectra is negligible.Funding for open access charge: Universidad de Málaga. We thank MINECO/FEDER of the Spanish Government (project reference PGC2018-098533-B-100) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the vibrational spectroscopy unit of the Research Central Services (SCAI) of the University of Ma´laga. O. G. acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 850836, ERC Starting Grant ‘‘PolyHelix’’

Electrochemical Route to Solution-Processable Polymers of Thiophene/Selenophene Capped Didodecyloxybenzo[1,2‑<i>b</i>:4,3‑<i>b</i>′]dithiophene and Their Optoelectronic Properties

Two new solution-processable polymers <b>P1</b> and <b>P2</b> are being reported here, which were prepared by electrochemical polymerization of thiophene and selenophene capped 7,8-didodecyloxybenzo­[1,2-<i>b</i>:4,3-<i>b</i>′]­dithiophene (BdT-Dod), respectively and characterized by gel permeation chromatography (GPC) and ¹H NMR. The selenophene containing polymer possesses lower band gap than the thiophene analogue. Density functional theory (DFT) calculation showed the highly curved structure of the polymers and reproduced the trend in their optical band gaps. <b>P2</b> showed larger bathochromic shift in the absorption spectrum from solution to film state compared to that of <b>P1</b>, which indicates better π-stacking interaction in the solid state for <b>P2</b>. In spite of having highly curved chains, the polymers successfully exhibited electrochromic switching. The exchange of the end-caps from thiophene to selenophene have manifested with higher electrochromic switching ability and better polaronic and bipolaronic features in spectroelectrochemical measurement of <b>P2</b> than that of <b>P1</b>. Kinetic study on the polymer films using chronoamperometry revealed that the selenophene containing polymer <b>P2</b> afforded Δ%<i>T</i> of ∼60 in the visible region with a coloration efficiency of 100 cm² C^–1. Electrochemical polymerization of BdT-Dod using different solvent/electrolyte systems was unsuccessful

Detrimental Ni(0) Transfer in Kumada Catalyst Transfer Polycondensation of Benzo[2,1-b:3,4-b ']dithiophene

© 2016 Wiley Periodicals, Inc. This article deals with the Kumada Catalyst Transfer Polycondensation (KCTP) of 4,7-dioctylbenzo[2,1-b:3,4-b']dithiophene (BDP-Oct) using Ni(II) catalyst or In/cat combination. A combination of MALDI MS, GPC, and 31P NMR spectroscopy is used to reveal the failure of the KCTP of this particular monomer. Intermolecular transfer reactions to monomer appeared to prevent the formation of polymer. This result is remarkable, since isomeric benzo[1,2-b:4,5-b']dithiophene polymerizes in a controlled way. The presence of a "non-aromatic double bond" in annulated monomers is discussed.status: publishe

Selenium-Based Drug Development for Antioxidant and Anticancer Activity

Selenium is one of the eight necessary trace elements humans require for active health balance. It contributes in several ways to the proper functioning of selenoprotein. Selenium has received enormous interest recently due to its therapeutic potential against a number of ailments. To date, numerous chemical compounds containing selenium have been investigated for the therapy of cancer and other disorders. Unifying the selenium atom into chemical components (typically organic) greatly increased their bioactivities. We foresee that the structure–property relationship of recently developed materials could significantly decrease the laborious work of background research to achieve target-oriented drug design in coming years. This review summarizes the research progress in the last 10 to 15 years and the application of selenium-containing compounds in the design and synthesis of those materials for potential antioxidant and anticancer agents.</b

Helically Locked Tethered Twistacenes

Twisting linear acenes out of planarity affects their electronic and optical properties, and induces chirality. However, it is difficult to isolate the effect of twisting from the substituent effect. Moreover, many twistacenes (twisted acenes) readily racemize in solution. Here, we introduce a series of twistacenes having an anthracene backbone diagonally tethered by an <i>n</i>-alkyl bridge, which induces a twist of various angles. This allows us to systematically monitor the effect of twisting on electronic and optical properties. We find that absorption is bathochromically shifted with increasing twist, while fluorescence quantum efficiency drops dramatically. The tethered twistacenes were isolated to their enantiomerically pure form, displaying strong chiroptical properties and anisotropy factor (<i>g</i>-value). No racemization was observed even upon prolonged heating, rendering these tethered twistacenes suitable as enantiopure helical building units for π-conjugated backbones

Helically Locked Tethered Twistacenes

Twisting linear acenes out of planarity affects their electronic and optical properties, and induces chirality. However, it is difficult to isolate the effect of twisting from the substituent effect. Moreover, many twistacenes (twisted acenes) readily racemize in solution. Here, we introduce a series of twistacenes having an anthracene backbone diagonally tethered by an <i>n</i>-alkyl bridge, which induces a twist of various angles. This allows us to systematically monitor the effect of twisting on electronic and optical properties. We find that absorption is bathochromically shifted with increasing twist, while fluorescence quantum efficiency drops dramatically. The tethered twistacenes were isolated to their enantiomerically pure form, displaying strong chiroptical properties and anisotropy factor (<i>g</i>-value). No racemization was observed even upon prolonged heating, rendering these tethered twistacenes suitable as enantiopure helical building units for π-conjugated backbones

Helically Locked Tethered Twistacenes

Twisting linear acenes out of planarity affects their electronic and optical properties, and induces chirality. However, it is difficult to isolate the effect of twisting from the substituent effect. Moreover, many twistacenes (twisted acenes) readily racemize in solution. Here, we introduce a series of twistacenes having an anthracene backbone diagonally tethered by an <i>n</i>-alkyl bridge, which induces a twist of various angles. This allows us to systematically monitor the effect of twisting on electronic and optical properties. We find that absorption is bathochromically shifted with increasing twist, while fluorescence quantum efficiency drops dramatically. The tethered twistacenes were isolated to their enantiomerically pure form, displaying strong chiroptical properties and anisotropy factor (<i>g</i>-value). No racemization was observed even upon prolonged heating, rendering these tethered twistacenes suitable as enantiopure helical building units for π-conjugated backbones

Helically Locked Tethered Twistacenes

Twisting linear acenes out of planarity affects their electronic and optical properties, and induces chirality. However, it is difficult to isolate the effect of twisting from the substituent effect. Moreover, many twistacenes (twisted acenes) readily racemize in solution. Here, we introduce a series of twistacenes having an anthracene backbone diagonally tethered by an <i>n</i>-alkyl bridge, which induces a twist of various angles. This allows us to systematically monitor the effect of twisting on electronic and optical properties. We find that absorption is bathochromically shifted with increasing twist, while fluorescence quantum efficiency drops dramatically. The tethered twistacenes were isolated to their enantiomerically pure form, displaying strong chiroptical properties and anisotropy factor (<i>g</i>-value). No racemization was observed even upon prolonged heating, rendering these tethered twistacenes suitable as enantiopure helical building units for π-conjugated backbones

Helically Locked Tethered Twistacenes

Twisting linear acenes out of planarity affects their electronic and optical properties, and induces chirality. However, it is difficult to isolate the effect of twisting from the substituent effect. Moreover, many twistacenes (twisted acenes) readily racemize in solution. Here, we introduce a series of twistacenes having an anthracene backbone diagonally tethered by an <i>n</i>-alkyl bridge, which induces a twist of various angles. This allows us to systematically monitor the effect of twisting on electronic and optical properties. We find that absorption is bathochromically shifted with increasing twist, while fluorescence quantum efficiency drops dramatically. The tethered twistacenes were isolated to their enantiomerically pure form, displaying strong chiroptical properties and anisotropy factor (<i>g</i>-value). No racemization was observed even upon prolonged heating, rendering these tethered twistacenes suitable as enantiopure helical building units for π-conjugated backbones