Fluorene acceptors with intramolecular charge-transfer from 1,3-dithiole donor moieties: novel electron transport materials

摘要

NO2 O2N X Y S S R R SMe NO2 O2N X Y S S R R NO2 O2N X Y S S R R S S R R CHO 1andash;g + CF3SO3 ndash; n n 2a, cndash;g R = CO2Me 3a, cndash;g R = SMe 4bndash;g R = Me 5g R = S(CH2)17Me 6a, cndash;g n = 0, R = CO2Me 7cndash;g n = 2, R = CO2Me 8g n = 2, R = SMe 9g n = 2, R = Me a X = Y = H b X = H, Y = CO2Me c X = H, Y = CN d X = H, Y = NO2 e X = NO2, Y = CO2Me f X = NO2, Y = CN g X = Y = NO2 40 30 20 10 0 0.1 1 10 400 500 600 700 800 l / nm S l / m2 Jndash;1 e / 103 dm3 molndash;1 cmndash;1 ( c) ( b) ( d) ( a) Fluorene acceptors with intramolecular charge-transfer from 1,3-dithiole donor moieties: novel electron transport materials Igor F.Perepichka,*a Dmitrii F. Perepichka,a Martin R. Bryce,*bdagger; Leonid M. Goldenberg,b Lyudmila G. Kuzrsquo;mina,c Anatolii F. Popov,a Antony Chesney,b Adrian J. Moore,b Judith A. K. Howardb and Nikolai I. Sokolovd a L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, Donetsk 340114, Ukraine b Department of Chemistry, University of Durham, Durham, UK DH1 3LE c Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow 117907, GSP-1, Russian Federation d Laboratory of Holography, Natural Faculty, University lsquo;Kievo-Mogilyanskaya Academyrsquo;, Kiev 254145, Ukraine The synthesis, solution redox behaviour and intramolecular charge transfer properties of novel D(NCHndash;CH)nNA compounds (n = 0, 1, 3; D and A are 1,3-dithiole and nitrofluorene moieties, respectively) are reported.Organic compounds with asymmetric p-electron delocalization exhibit properties such as non-linear optical effects (NLO), photoconductivity and electron transport properties.1 Electron acceptors of the fluorene series are widely used for optical information recording.2 It has been shown that fluorene acceptors substituted with a donor moiety can efficiently sensitise the photoconductivity of carbazole-containing polymers in the spectral region of intramolecular charge transfer (ICT) of the acceptors.3 Although 1,3-dithiole electron donor are well-known building blocks in conductive charge transfer salts,4 there are few reports of 1,3-dithioles as components of p-conjugated push-pull compounds.5 Herein we report a new series of D(NCHndash;CH)nNA compounds containing 1,3-dithioles and nitrosubstituted fluorenes as D and A moieties, respectively.Compounds 2ndash;9 were synthesised (Scheme 1) by condensation of the substituted fluorenes 1 with the appropriate dithiolium salts (for 2ndash;5) or aldehydes (for 6ndash;9) in DMF, (20ndash;70 deg;C, 0.5ndash;50 h; 30ndash;90).The intramolecular charge transfer (ICT) in these compounds is manifested in the appearance of long-wavelength absorbance bands in their electronic spectra (Fig. 1, Table 1). Increasing the acceptor character of the fluorene fragment with electron withdrawing substituents results in a bathochromic shift of the ICT band that can be described quantitatively by eqn. (1), where hnICT is the hnICT = hn0 ICT + r2ICT Ss2p (1) ICT energy defined by the maxima of the ICT band (lICT), hn0 ICT is hnICT for the reference compound (unsubstituted benzene rings in fluorenes, Ss2p = 0), r2 is a parameter showing ICT energy sensitivity to substituents, and Ss2p is a sum of s2p (nucleophilic constants of the substituents in the fluorene nucleus).The sensitivity parameter r2ICT shows only minor changes with changing the substituents in the 1,3-dithiole ring (2?3? 4) or with lengthening the CNC chain between the D and A moieties (2 ? 6 ? 7) (Table 1).The values of r2ICT Aring; 0.14ndash;0.17 eV are higher than that reported for 9-(4-phenyl- 1,2-dithiol-3-ylidene)fluorenes (0.12 plusmn; 0.01 eV).6 The structure of 3g was determined by X-ray analysis (Fig. 2).sect; As a result of ICT, the exocyclic C(9)NC(14) double bond is lengthened 1.395(5) Aring; and is close to that observed in another ICT compound of the fluorene series, i.e. 9-(acyano- a-dimethylaminomethylene)-2,4,5,7-tetranitrofluorene 1.388(4) Aring;.3b The distortions of the substituents in the fluorene ring are a result of the close contact between the nitro groups in positions 4 and 5.The dihedral angle between the planes of the fluorene five-membered ring and the 1,3-dithiole ring is 21.3deg;. Fig. 2 shows that the acceptor moieties in the molecules related by symmetry centres form stacks (interplanar distance 3.58 Aring;). Interstack interactions occur through weak contacts of the donor fragments; S(2b)middot;middot;middot;S(3a) and S(2a)middot;middot;middot;S(3b) distances are slightly shortened (3.543 Aring;) compared to double Scheme 1 Fig. 1 Electron absorption spectra for (a) 3g and (b) 8g in acetone, (25 deg;C) and spectral distribution of SDV for PEPC films sensitized by 5 mass of electron acceptors (c) 5g and (d) TNF Chem. Commun., 1998 819the van der Waals radius of sulfur (3.6ndash;3.7 Aring;).7 There are also weak intermolecular Smiddot;middot;middot;O contacts (3.25ndash;3.42 Aring;). The electrochemical redox properties of the compounds 2ndash;4 and 6 have been studied by cyclic voltammetry (Table 1).para; Compounds 2ndash;4 display two reversible single-electron reduction waves (E1 21 red = 21.44 ? 20.81 V, E1 22 red = 21.60 ? 21.02 V in the sequence a ? g).Third quasi-reversible or irreversible single-electron reduction E1 23 red = 2(1.88ndash;2.15) V and oxidation (E1 2 ox = +0.63ndash;0.70 V) processes were observed in some, but not all, cases. Insertion of an additional double bond between the A and D moieties (6) leads to a shift of both E1 21 red and E1 22 red by ca . 0.3 V to more cathodic potentials. Correlation analyses of E1 21 red and E1 22 red for compounds 2ndash;4 by eqn. (2), where E1 2 is the half-wave potential of reduction or E1 2 = E1 20 + r2CV Ss2p (2) oxidation of a compound, E1 20 is E1 2 for the reference compound (unsubstituted benzene rings in fluorenes, Ss2p = 0), and r2 is a parameter showing electrochemical potential sensitivity to substituents, gave good linear relationships (r = 0.98ndash;0.999); sensitivity parameters r2CV for the first and second reduction steps of compounds 2ndash;4 were close and lay in the region of 0.20ndash;0.24 V, which is slightly higher compared to r2CV for nitrosubstituted 9-aminomethylenefluorenes.3b The electron affinities obtained for compounds 2ndash;4 from their E1 21 red potentials8 are ca. 0.2 eV lower than for the corresponding 4,5-X,Y- 2,7-dinitrofluoren-9-ones, and for tetranitro substituted derivatives 2gndash;4g are ca. 2 eV. This characterises compounds 2ndash;4 as moderate acceptors.Due to the low solubility of compound 3g we tested the more soluble long-chain homologue 5g as a sensitiser in photothermoplastic storage media (PTSM) based on polyN- (2,3-epoxypropyl)carbazole (PEPC).middot; Fig. 1 shows the spectral distribution of the electrophotographic sensitivity (SDV) of PTSM on the basis of PEPC films sensitized by 5g and by 2,4,7-trinitrofluoren-9-one (TNF) which is widely used for these purposes.2b In contrast to TNF, for which SDV decreases with increasing wavelength in the visible region, 5g displays increased sensitivity in its ICT region.Excellent rheological properties of PTSM sensitised with 5g (diffraction efficiency for plane lightwave holograms hmax = 25) allowed the attainment of extremely high values of holographic sensitivity, Sh = 250ndash;300 m2 J21 at the level of h = 1 (He-Ne laser, l = 632.9 nm),** suggesting that this type of acceptor is extremely promising as sensitisers for hologram recording. We thank the EPSRC the Royal Society for funding (I.F. P., L. M. G. and L. G. K.), and the Royal Society for a Leverhulme Senior Research Fellowship (to J. A. K. H.). Notes and References dagger; E-mail: m.r.bryce@durham.ac.uk Dagger; All new compounds gave satisfactory mass spectra, 1H NMR spectra and elemental analysis. sect; Crystal data for 3g: C18H10N4O8S4, M = 538.54, triclinic, P�1, a = 9.079(1), b = 10.014(1), c = 12.806(2) Aring;, a = 108.61(1), b = 102.30(1), g = 103.06(1)deg; , V = 1022.4(4) Aring;3, Z = 2, Dc = 1.749 g cm23, F(000) = 548, l = 0.71073 Aring T = 150.0(2) K, R = 0.0580, wR = 0.1345 and goodness-of-fit 1.096, Drmax = 0.665 e Aring;23, Drmin = 20.588 e Aring;23.CCDC 182/778. para; ca. 1024 mol dm23 compound in dry DMA (2ndash;4) or CH2Cl2 (6), Pt working electrode, 0.2 mol dm23 Bu4N+PF62; all potentials were measured vs. Fc0/Fc+ couple as internal reference. middot; Details are the same as described in refs. 2(c) and 3(b). ** PTSM with 5 mass TNF gave hmax = 15 and Sh = 20 m2 J21 under the same conditions ref. 2(b). 1 D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1996, 94, 195; M.Matsui, K. Fukuyasu, K. Shibata and H. Muramatsu, J. Chem. Soc., Perkin Trans. 2, 1993, 1107; M. Matsui, K. Shibata, H. Muramatsu and H. Nakazumi, J. Mater. Chem., 1996, 6, 1113. 2 (a) D. F. Eaton, Top. Curr. Chem., 1990, 156, 200; (b) I. F. Perepichka, D. D. Mysyk and N. I. Sokolov, in Current Trends in Polymer Photochemistry, ed. N. S. Allen, M.Edge, I. R. Bellobono and E. Selli, Ellis Horwood, London, 1995, ch. 18, p. 318; (c) D. D. Mysyk, I. F. Perepichka and N. I. Sokolov, J. Chem. Soc., Perkin Trans. 2, 1997, 537. 3 (a) N. G. Kuvshinskii, N. G. Nakhodkin, N. A. Davidenko, A. M. Belonozhko and D. D. Mysyk, Ukr. Phis. Zh., 1989, 34, 1100; (b) I. F. Perepichka, A. F. Popov, T.V. Orekhova, M. R. Bryce, A. N. Vdovichenko, A. S. Batsanov, L. M. Goldenberg, J. A. K. Howard, N. I. Sokolov and J. L. Megson, J. Chem.Soc., Perkin Trans. 2, 1996, 2453. 4 T. Joslash;rgensen, T. K. Hansen and J. Becher, Chem. Soc. Rev., 1994, 23, 41; M. R. Bryce, J. Mater. Chem., 1995, 5, 1481; V. Khodorkovsky and J. Y. Becker, in Organic Conductors. Fundamentals and Applications, ed. J.-P. Farges, Marcel Dekker, New York, 1994, ch. 3, p. 75. 5 H. E. Katz, K. D. Singer, J. E. Sohn, C. W. Dirk, L. A. King and H. M. Gordon, J. Am. Chem. Soc., 1987, 109, 6561; M. Blanchard-Desce, I. Ledoux, J.-M. Lehn, J. Malthete and J.Zyss, J. Chem. Soc., Chem. Commun., 1988, 737; S. Inoue, Y. Aso and T. Otsubo, Chem. Commun., 1997, 1105 and references cited therein. 6 D. D. Mysyk and I. F. Perepichka, Phosphorus, Sulfur, Silicon, Relat. Elem., 1994, 95ndash;96, 527. 7 Y. V. Zefirov and P. M. Zorkii, Russ. Chem. Rev., 1989, 58, 421; R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384. 8 D. D. Mysyk, I. F. Perepichka, A. S. Edzina and O. Ya. Neilands, Latvian J. Chem., 1991, 727 (in Russian). Received in Cambridge, UK, 6th November 1997; revised manuscript received, 2nd February 1998; 8/00912K Table 1 Correlationsa of ICT energies of acceptors 2ndash;4, 6 and 7 using eqn. (1), spectral data for 2gndash;4g and 6gndash;9g and CV data for 2gndash;4g and 6g Compound hn0 ICT/eVb r2ICT/eVb lICT/nm b,c lICT/nm c,d 2 3.00 plusmn; 0.05 20.138 plusmn; 0.012 544 535 3 2.88 plusmn; 0.02 20.153 plusmn; 0.008 592 578 4 2.81 plusmn; 0.02 20.150 plusmn; 0.011 611 595 6 2.98 plusmn; 0.02 20.169 plusmn; 0.006 587.5 572 7 2.79 plusmn; 0.02 20.164 plusmn; 0.011 636 590 8 707 650 9 753 700 eICT/dm3 mol21 cm21 E1 21 red/Ve E1 22 red/Ve 9800 20.80 21.02 9700 20.81 21.04 8600 20.83 21.05 21 000 21.11 21.32 39 000 40 000 a r ! 0.985. b In 1,2-dichloroethane. c Spectral data for compounds 2gndash;4g and 6gndash;9g. d In acetone. e CV data for 2gndash;4g and 6g (see footnote para;). Fig. 2 Crystal packing of compound 3g; short intermolecular Smiddot;middot;middot;S and Smiddot;middot;middot;O contacts are shown by dashed lines 820 Chem. Commun., 1998