Hydroquinone–pyrrole dyads with varied linkers

• Hao Huang,
• Christoffer Karlsson,
• Maria Strømme,
• Martin Sjödin and
• Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 89–96, doi:10.3762/bjoc.12.10

• substantial changes in the HOMO–LUMO gap that correlated with the extent of conjugation found experimentally. The results of this work are expected to open up for use of the investigated compounds as components of redox-active materials in sustainable, organic electrical energy storage devices. Keywords

• reference compound spectra (Figure 5). According to DFT calculations (see Supporting Information File 2 for details), the HOMO–LUMO transition is allowed for all compounds and has π–π* character. The HOMO of DMB couples strongly to the pyrrole HOMO, resulting in increased HOMO energy in 1, cis-3c, trans-3c

• therefore a measure of the charge delocalization in the molecule. This effect can be viewed as an increased delocalized system that results in a lowering of the HOMO–LUMO gap, which can be traced by the red shifts of the highest wavelength absorption in UV–vis spectra (Table 1). The extent of conjugation

Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

• Diego M. Andrada,
• Nicole Holzmann,
• Thomas Hamadi and
• Gernot Frenking

Beilstein J. Org. Chem. 2015, 11, 2727–2736, doi:10.3762/bjoc.11.294

• coefficient at the Ccarb atom that makes it suitable for π-backdonation. The LUMOs of compounds 1, and 7–10 which are not displayed in Figure 2 are also π-orbitals which have a node at the Ccarb atom. The HOMO–LUMO energy difference varies considerably between 4.58 eV (4) and 1.55 eV (15). The small HOMO–LUMO

• gap of the diamidocarbene 15 comes from the very low lying LUMO which has been noted before [42]. There is clearly a correlation between the HOMO–LUMO energy difference and the calculated singlet–triplet gap of the compounds which are given at the bottom of Figure 2. The largest singlet–triplet (S/T

Synthesis and photophysical characteristics of polyfluorene polyrotaxanes

• Aurica Farcas,
• Giulia Tregnago,
• Ana-Maria Resmerita,
• Pierre-Henri Aubert and
• Franco Cacialli

Beilstein J. Org. Chem. 2015, 11, 2677–2688, doi:10.3762/bjoc.11.288

• reported [20]. Furthermore, these results suggest that the reduction process of 3·TM-βCD displays a semi-reversible behavior. The HOMO/LUMO energy levels in combination with the electronic potentials of the anodic indium tin oxide (ITO) glass substrate (−4.75 eV) and cathodic aluminum (−2.2 eV), prove that

• mg∙mL−1 in CHCl3 (a), and normalized emission spectra at 10−1 mg∙mL−1 and 10−3 mg∙mL−1 in CHCl3, (b) and (c), respectively. CV of 3 (a), 3·TM-βCD (b) and 3·TM-γCD (c) in 0.1 M tetrabutylammonium perchlorate (TBAClO4)/ACN solution at scan rate 20 mV∙s−1 and HOMO/LUMO energetic levels in addition to

Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics

• Alexander L. Kanibolotsky,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2015, 11, 1749–1766, doi:10.3762/bjoc.11.191

• units into a conjugated network is a standard way to narrow the HOMO/LUMO band gap and examples of such units include dioxopyrrolopyrrole (DPP) [17][18][19], benzodifuranone [20] and boron-dipyrromethene (BODIPY) [21][22]. As a different class of electroactive materials, TTF derivatives are well-known

• -acceptor into the conjugated backbone led to a polymer with a narrow optical band gap (Egopt = 1.32 eV in CH2Cl2 solution), with the expected lower value of Egopt = 1.26 eV in the film due to π–π stacking interactions. The value of the HOMO/LUMO levels (−5.13/−3.49 eV) in the film were noticeably different

• solution, hence an interpretable 1H NMR spectrum was only obtained in a mixture of CDCl3 with CS2. In CH2Cl2 solution, the chemically synthesised product showed a π–π* transition peak at 443 nm, with a HOMO–LUMO gap of 2.32 eV, a value very similar to that of the parent sexithiophene 53 [91]. For the

Synthesis and spectroscopic properties of β-triazoloporphyrin–xanthone dyads

• Dileep Kumar Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2015, 11, 1434–1440, doi:10.3762/bjoc.11.155

• attractive building blocks for supramolecular arrays. These molecules provide various desirable properties such as a rigid planar geometry, highly conjugated structures, intense electronic absorption and emission properties and small HOMO–LUMO energy gaps [1][2]. Additionally, the electronic properties of

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination

• Awatef Ayadi,
• Aziz El Alamy,
• Olivier Alévêque,
• Magali Allain,
• Nabil Zouari,
• Mohammed Bouachrine and
• Abdelkrim El-Ghayoury

Beilstein J. Org. Chem. 2015, 11, 1379–1391, doi:10.3762/bjoc.11.149

• . Packing diagram of L1 showing the orientation of the columns of head to tail dimers. UV–visible absorption spectra of ligands L1 and L2 (c 2.5 × 10−5 M in (dichloromethane/acetonitrile, 9:1, v/v)), room temperature. HOMO–LUMO Frontier orbitals representation for ligands L1 and L2. Cyclic voltammograms of

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• state and the HOMO–LUMO gap of these complexes [53]. Penta-coordinated cobalt(III)–salen complexes are high-spin complexes and spin-restricted calculations are insufficient to describe their electron configuration. In the hexa-coordinated [(2-hydroxyethoxy)CoIII(salen)(trichloroacetate)] complex, the

Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F₄TCNQ

• Raúl García,
• M. Ángeles Herranz,
• Edmund Leary,
• M. Teresa González,
• Gabino Rubio Bollinger,
• Marius Bürkle,
• Linda A. Zotti,
• Yoshihiro Asai,
• Fabian Pauly,
• Juan Carlos Cuevas,
• Nicolás Agraït and
• Nazario Martín

Beilstein J. Org. Chem. 2015, 11, 1068–1078, doi:10.3762/bjoc.11.120

• procedure explained in Supporting Information File 1. The corresponding transmission curves are shown in Figure 9. Notice that the molecular HOMO–LUMO gap was corrected, following the procedure previously reported [37]. The HOMO and all other occupied orbital energies were shifted by Σocc=−IP − εH +Δocc

• , while the LUMO and all other unoccupied orbital levels were shifted by Σvirt=−EA − εL +Δvirt. Here, Δocc (Δvirt) is the image charge correction for the occupied (unoccupied) states, εH (εL) is the Kohn–Sham energy of the gas phase HOMO (LUMO), and IP(EA) is the gas phase ionization potential (electron

A hybrid electron donor comprising cyclopentadithiophene and dithiafulvenyl for dye-sensitized solar cells

• Gleb Sorohhov,
• Chenyi Yi,
• Michael Grätzel,
• Silvio Decurtins and
• Shi-Xia Liu

Beilstein J. Org. Chem. 2015, 11, 1052–1059, doi:10.3762/bjoc.11.118

• HOMO–LUMO gap. In turn, the direct linkage of D and A units leads to an effective π-conjugation, thus substantially lowering the HOMO–LUMO gap. Moreover, the application in dye-sensitized solar cells was investigated, showing that the power conversion efficiency increases by the insertion of the phenyl

• -energy absorption band a higher extinction coefficient and a slight red shift by virtue of the more extended π-conjugation. Based on the onset of the lowest-energy absorption band, the HOMO–LUMO gap is estimated to be 1.82 eV for 1 and 1.86 eV for 2. Therefore, the values of their LUMO energy levels of

• −3.54 eV and −3.31 eV (Table 1) ensure an efficient electron injection from the photo-excited dyes to TiO2. As a consequence, the direct linkage of the D and A units leads to an effective π-conjugation and a planar molecular configuration, thus substantially lowering the HOMO–LUMO gap, while the

Chiroptical properties of 1,3-diphenylallene-anchored tetrathiafulvalene and its polymer synthesis

• Masashi Hasegawa,
• Junta Endo,
• Seiya Iwata,
• Toshiaki Shimasaki and
• Yasuhiro Mazaki

Beilstein J. Org. Chem. 2015, 11, 972–979, doi:10.3762/bjoc.11.109

• (+)-3 and (−)-3 should be (+)-(S)-3 and (−)-(R)-3, respectively. In the spectra, the intensive Cotton effect was observed at 270 and 316 nm as a bisignate couple, together with broad shoulder tails to ca. 500 nm. The Cotton effect associated with the HOMO–LUMO transition was relatively weak, presumably

• shift can be ascribed to the conjugation to the central allene moiety. As for the spectrum of 34+, the absorption maximum at 667 nm, assigned to the HOMO–LUMO transition in the TTF2+ moieties, was also red-shifted compared with the corresponding absorption maximum (637 nm) of 102+. Similarly, cationic

Trifluoromethyl-substituted tetrathiafulvalenes

• Olivier Jeannin,
• Frédéric Barrière and
• Marc Fourmigué

Beilstein J. Org. Chem. 2015, 11, 647–658, doi:10.3762/bjoc.11.73

• these observations and also show that the low energy HOMO–LUMO absorption band found in nitrile or ester-substituted TTFs is not found in TTF-CF3, where, as in TTF itself, the low energy absorption band is essentially attributable to a HOMO→LUMO + 1 transition. Despite relatively high oxidation

• energy transition is not the HOMO→LUMO transition but the HOMO→LUMO + 1 transition. Indeed, the LUMO in both molecules has a σ character while the LUMO + 1 has a π character. By contrast, the ester and cyano groups (−M EWG) are strongly conjugated with the π system to such a point that the order of the

• two lowest unoccupied orbitals is inverted. This inversion, with now a LUMO of π character, allows for a direct HOMO→LUMO optical transition in the two latter compounds. Besides, the −I inductive effect of the trifluoromethyl group stalilizes HOMO, LUMO and LUMO + 1 of TTF. As a consequence, its lower

On the strong difference in reactivity of acyclic and cyclic diazodiketones with thioketones: experimental results and quantum-chemical interpretation

• Andrey S. Mereshchenko,
• Alexey V. Ivanov,
• Viktor I. Baranovskii,
• Grzegorz Mloston,
• Ludmila L. Rodina and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2015, 11, 504–513, doi:10.3762/bjoc.11.57

• compounds with a dipolarophile are cycloaddition processes of type II (HOMO, LUMO controlled) [23][24][25]. In order to confirm the proposed reaction mechanism and to explain the experimental results, geometries of the stationary points (i.e., reagents, products, intermediates, and the appropriate

Functionalized branched EDOT-terthiophene copolymer films by electropolymerization and post-polymerization “click”-reactions

• Miriam Goll,
• Adrian Ruff,
• Erna Muks,
• Felix Goerigk,
• Beatrice Omiecienski,
• Ines Ruff,
• Rafael C. González-Cano,
• Juan T. Lopez Navarrete,
• M. Carmen Ruiz Delgado and
• Sabine Ludwigs

Beilstein J. Org. Chem. 2015, 11, 335–347, doi:10.3762/bjoc.11.39

• , especially the position of the HOMO level and the HOMO–LUMO band gap value are crucial for the applicability in different devices such as organic photovoltaics, organic field effect transistors, organic light emitting diodes or organic electrochromic windows [1][2][3][4][5][6]. There are different ways to

• tune HOMO–LUMO band gap values, mostly concerning the modification of the used monomers, for example by a rigidification of the conjugated system [7], the introduction of electron-withdrawing [8] or electron-donating groups [9][10] to the monomers or the increase of the quinoid character [11]. One

• are recorded at 532 nm in order to be in resonance with the lowest energy absorption band (HOMO–LUMO transition) of the neutral polymers and therefore out-of-resonance with the absorption bands of the oxidized species. In accordance with earlier work [51], the Raman spectrum of PEDOT exhibits a very

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene

• Laurence Burroughs,
• John Ritchie,
• Mkhethwa Ngwenya,
• Dilfaraz Khan,
• William Lewis and
• Simon Woodward

Beilstein J. Org. Chem. 2015, 11, 273–279, doi:10.3762/bjoc.11.31

• substituted tetracene 7j forms ribbons of herringbone structures. Estimates of the HOMO–LUMO data for 7 were taken from UV and CV measurements (see Table 3 and Supporting Information File 1), as well as by DFT calculations. Tetracenes 7d and 7f show the widest range in HOMO–LUMO perturbation while Eg opt. is

Synthesis and properties of novel star-shaped oligofluorene conjugated systems with BODIPY cores

• Clara Orofino-Pena,
• Diego Cortizo-Lacalle,
• Joseph Cameron,
• Muhammad T. Sajjad,
• Pavlos P. Manousiadis,
• Neil J. Findlay,
• Alexander L. Kanibolotsky,
• Dimali Amarasinghe,
• Peter J. Skabara,
• Tell Tuttle,
• Graham A. Turnbull and
• Ifor D. W. Samuel

Beilstein J. Org. Chem. 2014, 10, 2704–2714, doi:10.3762/bjoc.10.285

• levels for both families are similar, whereas, in general, the LUMO levels of the Y-Bn family are lower, leading to narrower electrochemical HOMO–LUMO gaps. Optical properties The optical properties of the oligomers were studied in dichloromethane solutions. An image of toluene solutions of both families

• . The optical and electrochemical HOMO–LUMO gaps are in good agreement for most compounds, the difference being greatest for the first members of the two series Y-B1 (0.25 eV) and T-B1 (0.10 eV). The emission spectra of the oligomers reveal a single band with its peak positioned at around 600 nm for the

• (2.42 Å and 2.44 Å) are also smaller than the sum of the van der Waals radii, also indicating the possibility of H–F interactions. The greater degree of planarity in Y-B1 leads to increased conjugation and therefore a lower HOMO–LUMO gap, which is predicted from the DFT calculations and is observed in

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells

• Diego Cortizo-Lacalle,
• Calvyn T. Howells,
• Upendra K. Pandey,
• Joseph Cameron,
• Neil J. Findlay,
• Anto Regis Inigo,
• Tell Tuttle,
• Peter J. Skabara and
• Ifor D. W. Samuel

Beilstein J. Org. Chem. 2014, 10, 2683–2695, doi:10.3762/bjoc.10.283

• one-pot reaction. Extending the conjugated π-system of a compound leads to a narrower HOMO–LUMO gap and a bathochromic shift of the absorption spectrum. Both effects are usually desirable to enhance the solar absorption. Therefore, an extended analogue of compound 6 with an additional thiophene ring

• charged states. The HOMO and LUMO energy levels were calculated from the onset of the first oxidation and reduction waves in both solution and solid state and used to determine the HOMO–LUMO gap. Due to the close interactions between molecules in the solid state, the HOMO–LUMO gap is expected to be lower

• compared to the HOMO–LUMO gap calculated from the studies in solution. Interestingly though, 9 and 10 show higher HOMO–LUMO gaps in the solid state. The film formation stabilises significantly the HOMO level of both triads (see Table 1), presumably through the interaction of the donor components of the

The effect of permodified cyclodextrins encapsulation on the photophysical properties of a polyfluorene with randomly distributed electron-donor and rotaxane electron-acceptor units

• Aurica Farcas,
• Ana-Maria Resmerita,
• Pierre-Henri Aubert,
• Flavian Farcas,
• Iuliana Stoica and
• Anton Airinei

Beilstein J. Org. Chem. 2014, 10, 2145–2156, doi:10.3762/bjoc.10.222

• , IP and EA compared to any of the constituents, which is necessary for electronic applications. The diagram with HOMO/LUMO levels and the work function of the indium tin oxide (ITO) coated glass substrates with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (anode) and Ca or Al

• properties of 4, 4a and 4b copolymers. Supporting Information FTIR spectra of the TMS-β-CD and copolymers, 1H NMR spectra of the TMS-β-CD, non-rotaxane 4 and 4b polyrotaxane copolymers, the fluorescence lifetimes of the non-rotaxane 4 and 4b polyrotaxane copolymers, the diagram with HOMO/LUMO levels of the

• , fluorescence lifetimes and the diagram with HOMO/LUMO energy levels of the copolymers. Acknowledgements This research was supported by a grant of the Romanian National Authority for Scientific Research, CNCS – UEFISCDI, project number PN-II-ID-PCE-2011-3-0035. A. F. acknowledges financial support from the

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• ) using Hückel molecular orbital theory [2][3], subsequently attributed by him to the positioning of conical intersections between the HOMO–LUMO PE surfaces [4][5]. He termed this phenomenon the “meta effect”, and generalized it for photochemical solvolysis reactions. Several additional photosolvolysis

Expeditive synthesis of trithiotriazine-cored glycoclusters and inhibition of Pseudomonas aeruginosa biofilm formation

• Meriem Smadhi,
• Sophie de Bentzmann,
• Anne Imberty,
• Marc Gingras,
• Raoudha Abderrahim and
• Peter G. Goekjian

Beilstein J. Org. Chem. 2014, 10, 1981–1990, doi:10.3762/bjoc.10.206

• known to significantly modify the HOMO–LUMO orbital energies, and thus change the redox potentials [31][32][33][34]. It also shifts the spectroscopic absorption and emission wavelengths and can lead to a phosphosrescence emission [33]. Additionally, an aza-aromatic core would improve water solubility by

Aryl substitution of pentacenes

• Andreas R. Waterloo,
• Anna-Chiara Sale,
• Dan Lehnherr,
• Frank Hampel and
• Rik R. Tykwinski

Beilstein J. Org. Chem. 2014, 10, 1692–1705, doi:10.3762/bjoc.10.178

• two other classes. Thus, the biggest influence of the pendent substituent appears to be related to the energy of the LUMO. As suggested by the UV–vis analyses (vide infra), the HOMO–LUMO gap estimated for pentacenes 3a–k by CV (1.94–2.02 eV) is larger than the HOMO–LUMO gap of TIPSPc (1.91 eV), while

• incorporation of the ethynyl spacer in 2a–c provides for the lowest HOMO–LUMO gap of the molecules discussed here. X-ray crystallographic analysis Typically, three predominant solid-state packing patterns are found by X-ray crystallographic analysis of pentacene and its derivatives [13]: a) a herringbone

Synthesis of new, highly luminescent bis(2,2’-bithiophen-5-yl) substituted 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole

• Anastasia S. Kostyuchenko,
• Vyacheslav L.Yurpalov,
• Aleksandra Kurowska,
• Wojciech Domagala,
• Adam Pron and
• Alexander S. Fisyuk

Beilstein J. Org. Chem. 2014, 10, 1596–1602, doi:10.3762/bjoc.10.165

• of each molecule, in which the order of bonds connecting the heteroaromatic units increases. The energy dissipated upon geometric relaxation of the excited molecule following the vertical HOMO–LUMO transition, prior to the return transition from S1 to S0 state, is manifested as a Stokes shift. Since

Theoretical studies on the intramolecular cyclization of 2,4,6-t-Bu₃C₆H₂P=C: and effects of conjugation between the P=C and aromatic moieties

• Masaaki Yoshifuji and
• Shigekazu Ito

Beilstein J. Org. Chem. 2014, 10, 1032–1036, doi:10.3762/bjoc.10.103

• (Figure 5). The TD-SCF calculation of 2 using CAM-B3LYP/DGDZVP conditions characterized the HOMO–LUMO transition at 289 nm with a relatively large absorption coefficient (f = 0.162). On the other hand, the absorption maximum of 2 was slightly blue-shifted in comparison with that of the Mes*-substituted

The Ugi four-component reaction as a concise modular synthetic tool for photo-induced electron transfer donor-anthraquinone dyads

• Sarah Bay,
• Gamall Makhloufi,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 1006–1016, doi:10.3762/bjoc.10.100

• the carbazole dyads 8e and 8f. Eventually, the absorption characteristics of phenothiazine dyads can be more easily red-shifted and, therefore, charge separation by PET should be accessible with visible light by fine-tuning the donor chromophore towards lower HOMO–LUMO gaps. Conclusion The Ugi four

Columnar/herringbone dual crystal packing of pyrenylsumanene and its photophysical properties

• Binod Babu Shrestha,
• Shuhei Higashibayashi and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2014, 10, 841–847, doi:10.3762/bjoc.10.80

• maximum of 1 was evidently red-shifted relative to those of 3 and pyrene. The 355 nm absorption band of 1 was assigned to the HOMO–LUMO transition by TD-DFT calculations (ωB97XD/6-31G(d)). DFT calculations also demonstrated that the HOMO and LUMO of 1 are primarily located on the pyrene moiety (Figure 4

• ). The dihedral angle between the sumanene and pyrene moieties resulting from calculations was 48.2°. This angle causes some extension of the π-conjugation to the sumanene moiety, resulting in a narrower HOMO–LUMO gap and the observed red shift in absorption. The emission of 1 in solution is also red

• spectra of 1, 3 and pyrene in CH2Cl2 solution (solid line) (1.0 × 10−5 M) and in the solid state (dotted line). Calculated HOMO and LUMO orbitals and HOMO–LUMO gaps (ΔE) for 1, 3 and pyrene (ωB97XD/6-31G(d)). Synthesis of pyrenylsumanene (1): (a) Sc(OTf)3 (5 mol %), DIH (100 mol %), CH2Cl2, rt, 2.5 h

Rapid pseudo five-component synthesis of intensively blue luminescent 2,5-di(hetero)arylfurans via a Sonogashira–Glaser cyclization sequence

• Fabian Klukas,
• Alexander Grunwald,
• Franziska Menschel and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 672–679, doi:10.3762/bjoc.10.60

• ) with a mean deviation of 0.05 eV (see Supporting Information File 1). Roughly a similar trend can be found for the HOMO–LUMO gap. The inspection of the coefficient densities in the Kohn–Sham frontier molecular orbitals of the compounds 2i, 2j, and 2n underlines that the HOMO and the LUMO are