Dmitrii F. Perepichka

Synthesis, Structures and Nonlinear Optical Properties of Novel D−π−A Chromophores: Intramolecular Charge Transfer from 1,3-Dithiole or Ferrocene Moieties to Polynitrofluorene or Dicyanomethylene Moieties through Conjugated Linkers

Electron donor−π−acceptor chromophores 5, 9, 11, 18−20, 21, 22, 27, 28a, 28c, 31, 32, 34−36, 38a−c, 41a, 41c, and 42 have been synthesised. The donor units are 1,3-dithiole and ferrocene; conjugated ethylenic, phenyl, phenylenevinylene, thienyl, bithienyl, terthienyl, or thienylenevinylene linkers act as a central π-electron relay unit, and dicyanomethylene and polynitrofluorene groups as the acceptor unit. The electronic absorption spectra display a broad low-energy intramolecular charge transfer band in the visible region (500−700xa0nm) the energy (hνICT ≈ 1.7−2.5xa0eV) and intensity (ϵ ≈ 5000−50000 M−1cm−1) of which depend substantially on the nature of both D and A moieties and on the structure of the linker unit. Nonlinear optical properties have been evaluated using the EFISH technique: the highest μβ(0) values are observed for 38b [(900±300)×10−48 esu] and 42 [(1800±300)×10−48 esu] establishing that polynitrofluorene is a promising acceptor terminal moiety in this context. The molecular and electronic structures of 49 and 50 have been calculated by the RHF/6-31G(d)//RHF/6-31G(d) ab initio method. The HOMO is located mostly in the 1,3-dithiolium ring, and the LUMO mostly at the dicyanomethylene fragment (and the phenyl ring of 50) although the electronic population at C2 of the 1,3-dithiolium rings is also considerable. The X-ray crystal structures of 9, 18 and 27 are reported. In all three structures the conjugated π-systems are effectively planar with extensive π-electron delocalisation between the donor and acceptor moieties. The planar conformation of 18 gives rise to a close intramolecular S···S contact of 3.095(3) A between the dithiole and thiophene units.

Engineering a Remarkably Low HOMO ± LUMO Gap by Covalent Linkage of a Strong -Donor and a -Acceptor-Tetrathiafulvalene- -Polynitrofluorene Diads: Their Amphoteric Redox Behavior, Electron Transfer and Spectroscopic Properties

Novel R3TTF-sigma-A compounds 14, 16 and 19 (R3TTF = trial-kyletrathiafulvalene, sigma = saturated spacer, A = polynitrofluoren-9-dicyano-methylene acceptor) incorporating very strong donor and acceptor moieties have been synthesized by condensation of the corresponding R3TTF-sigma-fluoren-9-one diads with malononitrile. Reversible five-step amphoteric redox behavior has been observed with an extremely low HOMO-LUMO gap (approximately 0.3 eV). For compound 14 a strong EPR signal is observed in the solid state, ascribed to intermolecular complexation: a less intense signal is seen in solution, corresponding to ca. 2% of the molecules existing in a radical form at room temperature. Intramolecular charge transfer in diads 14 and 16 is manifested in strong absorption bands in the near-IR region of their electronic spectra. Spectroelectrochemical data reveal marked electrochromic behavior in the visible and near-IR region of both compounds. The first X-ray crystal structure of a fluorene radical-anion salt is reported, namely the copper salt of 2,4,5,7-tetranitro-9- dicyanomethylenefluorene (1:1 stoichiometry).

Synthesis of Conjugated Tetrathiafulvalene (TTF)-π-Acceptor Molecules − Intramolecular Charge Transfer and Nonlinear Optical Properties

We have synthesised new conjugated donor-π-acceptor (D-π-A) chromophores 7, 9, and 12−15 in which monosubstituted tetrathiafulvalene (TTF) and trimethyl-TTF units are the donor moieties, connected by ethylenic bridges to electron-deficient benzene derivatives as the acceptor moieties. These compounds display a broad intramolecular charge transfer (ICT) band in their solution UV/Vis spectra at λmax = ca. 500xa0nm. The second order nonlinear optical (NLO) properties of these derivatives have been studied using the EFISH technique and calculated by semiempirical and ab initio theoretical methods. The effect of methyl substituents in the TTF moiety and the nature of the conjugated bridge are discussed. Analysis of the bond lengths obtained by an X-ray diffraction study of compound 9 reveal ICT in the solid state.

Electron acceptors of the fluorene series: Part 12. 9-(Metalloceneylidene)nitrofluorene derivatives of Fc–NF, NF–Fc–NF, and NF–Rc–NF types, and the vinylogues Fc–π–NF: synthesis, characterisation, intramolecular charge transfer, redox properties and X-ray structures for three fluorene–ferrocene derivatives

Reaction of ferrocenecarboxaldehyde 13 and its vinylogue, (E,E)-1-ferrocenyl-4-formyl-1,3-butadiene (16), with nitrofluorenes as CH-acids, results in push–pull compounds of the type Fc– –fluorene (8a –g, 12a–e). Similar reaction with bifunctional ferrocene and ruthenocene dicarboxaldehydes results, depending on the fluorene structure, in the products of mono- or di-condensation, OHCFcCHfluorene (11d,e) or fluoreneCHFcCHfluorene and fluoreneCHRcCHfluorene (9a –c, 10a–c). Intramolecular charge transfer (ICT) in compounds 8 results in lowering the rotation barrier around the CHfluorene double bond and easy E – Z isomerisation in solution. Cyclic voltammetry (CV) experiments show a reversible single-electron oxidation of FcCHfluorenes (8) yielding the cation and two reversible single-electron reduction waves yielding the radical anion and dianion (for 8a –e) which merge into one two-electron reduction wave for 8f–h. ICT was also manifested in the electron absorption spectra of 8– 12 ,a nd energies of ICT (as well as reduction potentials in CV) were found to display excellent correlation (r 0.99) with Hammett-type substituents constants ( p − ) in the fluorene moiety. Compounds 8–12 show solvatochromism [8a: ICT= 604.5 nm (acetonitrile), 622.5 nm (1,2-dichloroethane)], with, however, no quantitative regularities for 10 solvents of different polarity. Bathochromic shifts of 40–83 nm and an increase in the intensity of ICT bands were observed with lengthening of the -bridge between ferrocene and fluorene moieties (812) whereas substitution of the ferrocene unit in 9 by the ruthenocene unit (10) resulted to a hypsochromic shift of ca. 100 nm due to decreasing donor ability of the latter metallocene fragment. Acceptor 8a was found to sensitise the photoconductivity of poly-N-(2,3-epoxypropyl)carbazole showing moderate holographic response of the materials. Molecular and crystal structures for ferrocene derivatives 8a, 8g ,a nd11d were determined by single-crystal X-ray diffraction. Tetranitro derivative 8a shows substantial distortion, caused by steric repulsion between the nitro groups in positions 4 and 5, which precludes the formation of stacks, and pairs of fluorene moieties contact face-to-face (interplanar distance 3.8 A ). In di- and trinitro derivatives 8g and 11d the fluorene moieties are more planar and their crystal packing motifs are similar: fluorene moieties form good stacks, parallel to the x-axis in 8g and the y-axis in 11d, with interplanar separations between fluorene moieties of 3.35–3.36 A for 8g and alternate separations of 3.52 and 3.55 A for 11d.

π-Extended nitrofluorene-1,3-dithiole chromophore: enhancing the photoresponse of holographic materials through the balance of intramolecular charge transfer and electron affinity

The synthesis, electrochemistry, and electron absorption spectra of the novel push–pull type acceptor, 9-{[4,5-bis(hexylthio)-1,3-dithiol-2-ylidene]ethylidene}-2,4,5,7-tetranitrofluorene 3 is reported. A bathochromic shift and increased intensities of intramolecular charge transfer bands (compared to 1) are well-balanced with the electron affinity of the acceptor, which results in a pronounced increase of the photoresponse of carbazole-containing photothermoplastic optical information storage materials in the long wavelength visible and near infrared regions.

Arene–perfluoroarene interactions in crystal engineering. 5.

In the title complex, C(10)F(8) x C(6)H(4)S(4), planar centrosymmetric molecules of tetrathiafulvalene and octafluoronaphthalene, inclined to each other by 9.6 (1) degrees, form a mixed stack which does not exhibit charge transfer. Adjacent stacks pack in a herring-bone motif.

Electron acceptors of the fluorene series. Part 13. 9-(5-Nitrofuran-2-ylidene)- and 9-(5-nitro-2-thienylidene)-2,4,5,7-tetranitrofluorenes: novel π-extended electron acceptors. Synthesis, cyclic voltammetry and X-ray crystal structures for the acceptor and its 4,5-dimethyltetrathiafulvalene complex, and a theoretical study

Two novel polynitrofluorene acceptors π-extended with 5-nitrofuran and 5-nitrothiophene moieties (2 and 3), have been synthesised. Cyclic voltammetry experiments show single electron reduction peaks at ca. n−0.66–0.67 V (vs. Fc/Fc+); however, this process (probably due to substantial changes in geometry of reduced species) is electrochemically irreversible and re-oxidation of the derived radical anions is observed at +0.05 and −0.04 V, for 2 and 3, respectively. Electronic absorption spectroscopy confirms charge transfer complexation of the studied acceptor with 4,5-dimethyltetrathiafulvalene (Me2TTF) in solution. The X-ray crystal structure of the 1xa0∶xa01 charge transfer complex (CTC) of acceptor 2 nwith Me2TTF shows mixed A⋯D⋯A⋯D stacking, and its comparison with the structure of the acceptor itself indicates a neutral ground state of this CTC. Theoretical HF/6-31G(d) calculations for the acceptor 2 and its radical anion and dianion states are in agreement with this conclusion. Intramolecular hydrogen bonding in 2 between the oxygen of the furan ring and C(8)-H hydrogen of the fluorene moiety is observed in both solution (1H NMR) and solid state (X-ray) and also supported by theoretical calculations

Methoxy­carbonyl­methyl 3-hydroxy-2-(methoxy­carbonyl)­benzo­[b]­furan-6-carboxyl­ate

The title compound, C14H12O8, exists in the crystal structure in the enol form, as hydrogen-bonded dimers.