Push–Pull Triphenylamine Chromophore Syntheses and Optoelectronic Characterizations
Victorien Jeux, Olivier Segut,* Dora Demeter, Olivier AlvÞque, Philippe Leriche,* and Jean Roncali*
[a]Introduction
Push–pull systems based on triarylamine donor (D) blocks con- nected to electron-acceptor (A) units through p-conjugating spacers of variable structure and composition have been the focus of sustained interest for a long time.[1–8] Widely investi- gated for second-order nonlinear optics,[1]such D–p–A systems have attracted much attention as sensitizers for dye-sensitized solar cells (DSSCs),[2]and more recently as donor materials in organic solar cells (OSC).[3]
In this context, we have developed several series of triaryla- mine[4] derivatives of various structures involving star-shaped systems with peripheral acceptor groups,[5] linear push–pull compounds,[6, 7] and some hybrid combinations of these two architectures.[8]Recently, several groups have reported the syn- thesis and evaluation of photovoltaic performances of push–
pull systems combining low molecular weight, structural sim- plicity, and high overall yield of synthesis.[9]
In our continuing interest in the design of small and simple molecular D–A systems based on triarylamine donor blocks, we report here on the synthesis and properties of a set of nine push–pull molecules terminated by a dianisylamino donor group. They differ from their two-ring p-conjugating spacers, namely, phenylthienyl (PT) and dithienyl (TT), and by the strength and structure of their terminal electron-deficient group (Scheme 1). Thus, five different electron-deficient termi- nations have been studied (Scheme 1).
After the description of the synthesis of target compounds, the UV-visible absorption spectroscopy and cyclic voltammetry
[a]V. Jeux, O. Segut, D. Demeter, O. AlvÞque, P. Leriche, J. Roncali Universit d’Angers
MOLTECH-Anjou, UMR CNRS 6200 2 Boulevard Lavoisier, 49045 Angers (France) E-mail: [email protected]
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cplu.201402386&please give academic titles for authors&.
A series of push–pull molecules combining a diarylamine donor block with various electron-acceptor units through phe- nylthienyl (PT) and bithienyl (TT) p-conjugating spacers have been synthesized. Optical and electrochemical results, support- ed by theoretical calculations, show that the electronic proper- ties of the molecules can be modulated by varying the strength of the acceptor group and/or the structure of the
conjugating spacer. As a first try to estimate&first evaluation
of&the potential of these compounds as donors in organic
solar cells (OSC), simple planar heterojunction (PHJ) prototypes using fullerene C60as electron acceptor have been fabricated.
Most OSCs exhibit analogous photoconversion efficiencies in the 1.5–2 % range. Their characteristics are discussed in terms of structure–properties relationships.
Scheme 1.Chemical structures and syntheses of the target molecules.
&Conditions a,b,c made more explicit; ok? Scheme reorganized to fit in
one column&
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analyses associated with theoretical calculations allow under- standing of the relationships between their structures and op- toelectronic properties. As a first approach to evaluate their potential as material for OSC, the compounds have been incor- porated as donors in planar heterojunction solar cells (PHJ) using fullerene C60as the electron acceptor. Despite very analo- gous structures, subtle differences in performances are ob- served and can sometimes be explained in terms of structure–
properties relationships.
Results and Discussion
Synthesis
The aldehydes PT-CHO[10] and TT-CHO[7] were synthesized by using known procedures. The target compounds were ob- tained by a Knoevenagel condensation of the aldehydes with malononitrile, thiobarbituric acid, indanedione, dicyanovinylin- danone, and bis(dicyanovinylindane). All compounds were soluble enough for a classical purification by chromatography and were isolated in 51–80 % yields (see the Supporting Infor- mation). The overall yields after four to five synthetic steps from commercially available products were between 22 and 36 %.
Optical and electrochemical properties
The electronic properties of the nine compounds have been analyzed by UV-visible absorption spectroscopy (10 5m in di- chloromethane) and cyclic voltammetry in dichloromethane in the presence of 0.10m tetrabutylammonium hexafluorophos- phate as supporting electrolyte. The corresponding results are listed in Table 1.
The UV-visible absorption spectra of the compounds exhibit two bands in the 270–450 nm region followed by a broader and more intense band (bold values in Table 1) in the 500–
700 nm region assigned to an internal charge transfer. All com- pounds present molar extinction coefficients (e) in the range of 40 000–50 000 L mol 1cm 1. For a given spacer, the maximum of the intramolecular charge transfer (ICT)&&ok?&& band (lmax) presents considerable variations with the strength of the
acceptor end group. Thus, replacing the dicyanovinyl group of PT-DCV with the bis(dicyanovinylindane) in PT-I2CN leads to a bathochromic shift of lmax from 519 to 701 nm (Table 1, Figure 1). Similarly, in the TT series, lmaxshifts from 576 nm for TT-DCV to 707 nm for TT-ICN.
In contrast, the structure of the p-conjugating spacer also strongly affects the absorption spectrum. Thus, for a given ac- ceptor group, the replacement of the PT by the TT spacer pro- duces a bathochromic shift oflmaxowing to the combined ef- fects of 1) the lower aromatic resonance energy of the thio- phene ring versus the phenyl one, 2) the suppression of the approximately 208dihedral angle associated with the steric in- teractions in the thiophene–benzene linkage with adoption of planar spacer geometry, and 3) the stronger donor effect of the thienyl group. Consequently, the optical gap of com- pounds in solution (DEopt, Table 1) oscillates between 1.76 eV for TT-ICN and 2.39 eV for PT-DCV, respectively.
Films of the various push–pull compounds were spin-cast on glass from solutions in dichloromethane. As molecular com- pounds are generally known for their high crystallinity, triphe- nylamine-based derivatives also present good film-forming properties[4] leading to homogeneous thin films. In each case, the passage from the solution to the solid-state is accompanied with a redshift of lmax
and a broadening of the absorption bands due to intermolecular interactions in the solid state. The various compounds present moderate (1.80–1.90 eV) or even low (1.30–1.40 eV) optical bandgaps (Eg) esti- mated from the long-wavelength absorption edge (Table 2 and the Supporting Information).
The cyclic voltammograms of the compounds present a first reversible oxidation wave followed by a second reversible or quasi-reversible oxidation pro- cess (Figure 2). In the negative potential region, the CV of all compounds presents a non-reversible re- duction process. The anodic peak potential (Epa) as- sociated with the first oxidation process is almost in- Table 1.UV-visible, absorption, and cyclic voltammetry data of the target com-
pounds.
Compd lmax
[a] DEopt[a] Log (e)[a] Epa
[b] Epc
[b]
[nm] [eV] [m1cm 1] [V] [V]
PT-DCV 276; 355;519 2.39 4.44 0.73 1.17
TT-DCV 299; 365;576 2.15 4.53 0.69 1.18
PT-TBB 279; 405;573 2.17 4.68 0.71 0.96
TT-TBB 269; 410;639 1.94 4.76 0.65 0.95
PT-I 268; 387;547 2.27 4.61 0.70 1.06
TT-I 272; 384;607 2.04 4.59 0.63 1.04
PT-ICN 284; 440;632 1.96 4.74 0.72 0.82
TT-ICN 280; 443;707 1.76 4.78 0.65 0.86
PT-I2CN 276; 348;701 1.77 4.63 0.73 0.49
[a] 1 10 5min CH2Cl2. [b] In 0.10mBu4NPF6/CH2Cl2, scan rate 100 mV s 1; reference SCE.
Figure 1.UV-visible absorption spectra recorded in CH2Cl2(1 105mof sub- strate). Solid line: PT-DCV; long dashed: PT-I; points: PT-TBB; short dashed:
PT-ICN; dash-dot-dot-dash: PT-I2CN.
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dependent of the strength of the acceptor group. However, the replacement of the PT by the TT spacer produces an ap- proximately 50–70 mV negative shift ofEpa, and the second ox- idation process becomes reversible (Figure 2 and the Support- ing Information).
In contrast, the nature of the electron-acceptor group exerts a marked effect on the potential of the cathodic peak potential Epc, which shifts from approximately 1.20 V to about 0.80 V when the dicyanovinyl group of PT-DCV is replaced by the di- cyanovinylindanone (PT-ICN). However, comparison of the data for compounds of the PT and TT series shows that the structure of the p-conjugating spacer has practically no effect on Epc, which suggests that the LUMO is essentially localized on the acceptor group.
Geometric optimization
Ab initio quantum calculations of compounds were performed with the Gaussian 03 package of programs at a hybrid density functional theory (DFT) level and carried out using the B3LYP/
6-31G(d,p) level. The optimized geometries of all compounds are similar to that of PT-TBB (Figure 3). As generally observed for TPA derivatives, the three central N C bonds are coplanar, which is characteristic of enamines. Steric hindrance between the aromatic rings grafted on the central nitrogen atom gener- ates the typical propeller shape of the molecules. A shortening of single bonds and lengthening of double bonds, typical from internal charge transfer, is observed in the p-conjugating
spacer. Compounds of the TT series present a nearly planar conjugated spacer whereas, owing to higher steric hindrance, compounds of the PT series present a twist angle of 13–208between the thiophenic and phenyl rings.
Figure 3 also presents the distribution of the HOMO and LUMO of PT-TBB. As the HOMO is delo- calized on the whole molecule with smaller coeffi- cients on the acceptor group, the LUMO is essential- ly localized on the electron-withdrawing part of the molecule. The calculated energy levels of the high- est-occupied (HOMO) and lowest-unoccupied orbi- tals (LUMO) as well as the corresponding energy gap (DEc) are collected in Table 2. The latter also presents the values of the experimental HOMO and LUMO
levels calculated from CV and UV-visible data as well as the bandgap of the films (Eg).[11]
The larger values ofDEcversus DEoptandEgreflect the fact that calculations refer to gas-phase molecules. There is never- theless a good agreement between calculated and experimen- tal results. The replacement of the PT spacer by TT produces a moderate destabilization of the calculated HOMO level (0.03–
0.07 eV) associated with a smaller increase of the LUMO (0.00–
0.04 eV) leading to a slight decrease ofDEc. This result is con- sistent with the stronger electron-donor effect of the thio- phene ring versus the phenyl one. The increase of the strength of the acceptor end group produces a marked reduction of DEc. In this case, a stabilization of both the calculated HOMO and LUMO is observed with a larger effect for the latter in agreement with a preferential localization of the LUMO on the acceptor part.
Experimental HOMO and LUMO present analogous evolu- tions with subtle differences. Thus, as the nature of thep-con- jugating spacer has only a moderate influence on the calculat- ed LUMO levels, the latter appears more important for mea- sured ones. On the contrary, theoretical HOMO levels are less perturbed by the acceptor strength than calculated ones.
Either way, theory and experiments confirm that the lowest gap is observed for PT-I2CN. However, the expected stabiliza- tion of the HOMO is not observed in that case owing to the Table 2.Calculated and experimental values of the energy levels of the frontier orbi-
tals and energy gaps.
HOMO LUMO DEc HOMO[a] LUMO[b] Eg
Compd [eV] [eV] [eV] [eV] [eV] [eV]
PT-DCV 5.06 2.64 2.42 5.72 3.33 1.89
TT-DCV 5.01 2.64 2.37 5.68 3.53 1.74
PT-TBB 4.98 2.62 2.36 5.70 3.53 1.79
TT-TBB 4.93 2.61 2.32 5.64 3.70 1.63
PT-I 4.83 2.38 2.45 5.69 3.42 1.85
TT-I 4.76 2.38 2.38 5.62 3.58 1.66
PT-ICN 5.00 2.91 2.09 5.71 3.75 1.58
TT-ICN 4.95 2.95 2.00 5.64 3.88 1.42
PT-I2CN 5.17 3.22 1.95 5.72 4.00 1.27
[a] Calculated form CV dataEHOMO= [Eox(V/SCE)+4.99]. [b] Calculated from CV and optical data,ELUMO=DEopt+EHOMO.
Figure 2.Cyclic voltammograms recorded in 0.10mBu4NPF6/CH2Cl2, scan rate 100 mVs1(V vs. SCE): left: PT-TBB, right: TT-TBB.
Figure 3.Top: Geometric optimization of PT-TBB (twist angle, 148). Bottom : DFT-calculated orbitals of PT-TBB. Left: HOMO ; right: LUMO.
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distortion associated with steric interactions between the bis(- dicyanovinylindane) block and the adjacent thiophene. It is also worth noting that this latter compound presents a mea- sured LUMO level of 4.0 eV, which is close to that of fullerene ( 4.1 eV) and hence not propitious to electron transfer in devi- ces. This last observation also explains why TT-I2CN was not synthesized nor studied.
Fabrication and characterization of photovoltaic devices
In a first approach to estimate the electronic properties of these molecules, they have been incorporated as the donor material in simple organic planar heterojunction (PHJ) solar cells of structure: ITO/PEDOT:PSS/donor/acceptor/aluminum (ITO=indium–tin oxide; PEDOT=poly(3,4-ethylenedioxythio- phene; PSS=polystyrene sulfonate), using fullerene C60as elec- tron acceptor. Although solution-processed bulk heterojunc- tion solar cells (BHJ) lead in general to higher power conver- sion efficiency (PCE) than that in PHJ solar cells, BHJ require lengthy optimization and large amounts of donor material and therefore are not the most convenient tool for a first screening of structure–properties relationships in a large series of com- pounds.
Table 3 lists the main photovoltaic characteristics of the devi- ces under AM 1.50 simulated solar illumination and Figure 4 shows representative examples of the current versus voltage
curves and external quantum efficiency (EQE) of the bilayer cells. The photoresponse of the cell shows a first band around 400 nm containing some contribution of fullerene followed by a second band centered on 640 nm in the 550–750 nm region that corresponds to the ICT band of the donor.
For each donor, the cells have been subjected to thermal an- nealing in optimized conditions (see the Experimental Section), which produced a net improvement of PCE owing to a simulta- neous increase of the open-circuit voltage (Voc) and short-cir- cuit current density (Jsc) (Figure 4).
In this series, owing to the strong isostructurality of com- pounds that lead to close HOMO and LUMO levels, the influ- ence of the structure on OSC performances remains subtle and subject to caution. Nevertheless, as shown in Table 1,Vocclearly increases with the strength of the acceptor group. It is general-
ly accepted that Voc depends on the difference between the HOMO of the donor and the LUMO of the acceptor.[12]Conse- quently it could be anticipated thatVoc would increase as the HOMO level of the donor decreases and hence with the in- crease of the oxidation potential of the donor. Thus, for exam- ple,Vocincreases from 0.75 to 0.78 V for the cells based on PT-I and PT-ICN, respectively. In contrast, for a given acceptor group, compounds of the TT series present higher HOMO levels and lead to cells exhibiting lowerVocthan derivatives of the PT series. The impact of structural modifications on FF and Jscis less evident. Although all cells have moderate fill factors (FF), it can be seen that the donors with a TT spacer lead to slightly higher FF values. On the contrary, except for the cells based on TT-DCV (see below), the Jscare in the range of 4.0–
6.0 mA cm 2 and donors of the TT series lead to lower values than the PT-based ones. Thus, even if the influence of the structure of the compound onVocappears clear, the opposite effect of the conjugating spacer on other characteristics leads to close PCE values, all in the 1.1–2.1 % range.
Two series of OSC lead to PCE values higher than 2 %. For PT-TBB, a Voc value of 0.79 V corresponded to a Jsc value of 5.64 mA cm 2and a FF of 41 %, which leads to a PCE of 2.04 %.
Table 3.Photovoltaic characteristics of the cells ITO/PEDOT:PSS/donor/
C60/Al under AM 1.5 simulated solar light.
Compd Annealing Voc Jsc FF PCE
T[8C] [V] [mA cm 2] [%] [%]
PT-DCV[7] 115 0.71 5.88 32 1.47
TT-DCV[7] 115 0.59 8.25 39 2.07
PT-TBB 155 0.79 5.64 41 2.04
TT-TBB 130 0.64 3.86 43 1.16
PT-I 120 0.75 4.69 47 1.82
TT-I 95 0.62 3.31 50 1.13
PT-ICN 135 0.78 4.76 45 1.82
TT-ICN 120 0.62 4.23 47 1.38
PT-I2CN 140 0.57 1.13 33 0.24
Figure 4.Top: Current density versus voltage curves for a bilayer cell PT-ICN/
C60in the dark (filled black circles) and under AM 1.5 simulated solar light with a power light intensity of 90 mW cm 2. Before (open gray circles) and after annealing (open black circles) at a power of 90 mW cm 2. Bottom : Ex- ternal quantum efficiency of the annealed cell under monochromatic irradia- tion.
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For both series, the highestJsc values are obtained with com- pounds containing the dicyanovinyl end group. Thus, the best PCE (2.07 %) is obtained with TT-DCV, which allows the highest Jscof 8.25 mA cm 2associated with aVocand a FF of 0.59 V and 0.39, respectively. This compound, which is expected to pres- ent the most planar geometry among the series, appears as the most propitious for efficient intermolecular interactions and hence charge transport. However, this hypothesis needs to be confirmed by further studies.
Contrary to other compounds that allow reasonable PCE, PT- I2CN only allows 0.24 % to a lowJscof 1.13 mA cm 2and a Voc of 0.57 V not related to its HOMO level. As previously outlined, this behavior can be ascribed to the strong electron affinity of this compound, which appears too close to that of fullerene.
Consequently, the ICN acceptor group appears as the limit of acceptor strength still compatible with such a photoinduced charge transfer with C60as acceptor. However, comparison of the results obtained with the two types of spacers shows that although the TT spacer leads to materials with lower bandgap, these better light-harvesting properties do not produce the ex- pected improved photovoltaic efficiency owing, in particular, to a decrease of the cell voltage associated with a higher HOMO level.
Conclusion
To summarize, a series of conjugated systems based on a diani- sylamino donor group and various electron acceptors connect- ed by means of two types ofp-conjugating spacers has been synthesized and characterized. These compounds are obtained in high overall yields and combine easy purification, adjustable energy levels, and processability. Spectroscopic and electro- chemical studies supported by theoretical calculations confirm the potential interest of these compounds, which present HOMO and LUMO levels (except PT-I2CN) suitable for integra- tion as donors in OSC. A first analysis of results obtained with OSC based on the nine compounds leads to PCE in the 1.1–
2.1 % range, which does not allow the best conjugating spacer or electron-demanding termination to be indicated unambigu- ously&&ok?&&. Although the correlation between the HOMO energy levels of the molecules, related to the nature of the conjugating spacer or termination, and the cell voltage ap- pears clear, the structural influence on Jsc and FF remain un- clear. Nevertheless, this study clearly shows that indanone (I and ICN) and thiobarbituric (TBB) electron-withdrawing groups, currently underexploited for OSC fabrication, are good candi- dates for new chromophoric systems.
Experimental Section
General
Solvents were purified and dried using standard protocols.1H and
13C NMR spectra were recorded on a Bruker Avance DRX 300 spec- trometer; d are given relative to tetramethylsilane, and coupling constants (J) in Hertz. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded by using a Bruker Biflex-III, equipped with a N2 laser (337 nm). For the
matrix, dithranol in CH2Cl2was used. High-resolution mass spectra were recorded in FAB mode on a Jeol JMS 700 spectrometer.
UV-visible optical data were recorded with a PerkinElmer lambda 950 spectrophotometer. Thermal analyses were performed using a DSC 2010 CE (TA Instruments). Cyclic voltammetry was per- formed with a biologic SP-150 potentiostat using a standard three- electrode cell with platinum working and counter electrodes and a saturated calomel electrode (SCE) as a reference.
Device fabrication and characterization
Fullerene C60(99+%) was purchased from Merck and used as re- ceived. The Baytron suspension used to apply smoothing and hole conducting/injecting layers was purchased as “Baytron P PE FL”
(HC Stark). All thin-film devices were prepared under laboratory conditions. As electrodes, ITO-coated glasses (20W/&, Solem) and evaporated Al films (ca. 150 nm thick) were used. The ITO electro- des were cleaned in ultrasonic baths, subjected to a UV–ozone treatment (15 min), and then modified by a spin-cast layer of Bay- tron (40 nm thick), which was dried at 1158C for 30 min. The Bay- tron suspension was filtered through a 0.45mm membrane (Minis- art RC 15, Sartorius) just prior to casting. The donor layer was spin- cast from solutions of the compound in chloroform (5 mgL 1) onto ITO slides initially precoated with a 40 nm PEDOT-PSS layer. Then, a layer of C60(30 nm) was deposited by thermal evaporation under high vacuum. A 150 nm-thick layer of Al was finally thermally evaporated through a shadow mask, at a pressure of approximate- ly 1 10 6mbar. The mask geometry defined a device area of 0.28 cm2. Each ITO-coated glass supports two individual devices.
For each compound, a minimum of 16 cells (8 substrates contain- ing 2 cells) were characterized. All devices were thermally treated.
A sacrificed cell was first heated for 5 min at 808C and the temper- ature was then increased by increments of 108C until the PCE begins to decrease. Then, the other cells were directly heated at the optimized temperature for 5 min.
After preparation, the devices were stored and characterized in an argon glovebox (200B, MBraun). TheJ–Vcurves were recorded in the dark and under illumination using a Keithley 236 Source Mea- sure unit and a home-made acquisition program. The light source was an AM 1.5 Solar Constant 575 PV simulator (Steuernagel Licht- tecknik, equipped with a metal halogenide lamp). The light intensi- ty was measured by a broad-band power meter (13PEM001, Melles Griot). The efficiency values reported here are not corrected for possible solar simulator spectral mismatch nor for the reflection/
absorbance of the glass/ITO/Baytron-coated electrodes.
Synthetic procedures and characterization of target com- pounds
The aldehydes PT-CHO and TTCHO as well as PT-DCV and TT-DCV were prepared as already reported.[7]
5-[(5-{4-[Bis(4-methoxyphenyl)amino]phenyl}thiophen-2-yl)- methylene]-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)- dione (PT-TBB): PT-CHO (0.326 g, 0.79 mmol) was dissolved in a so- lution of diethylthiobarbituric acid (0.18 g, 0.9 mmol) in dry CHCl3
(50 mL). Three drops of triethylamine were added and the solution was stirred at room temperature. After 24 h, the reaction mixture was diluted with CH2Cl2, and washed with a solution of sodium hy- droxide (1m), water, and brine. After removal of the solvent the residue was subjected to chromatography on silica gel treated with triethylamine (1 %) using dichloromethane as eluent to afford
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a dark solid (256 mg, 56 %). M.p. 195–1998C; 1H NMR (300 MHz, CDCl3):d=8.61 (s, 1 H), 7.83 (d,J=4.2 Hz, 1 H), 7.61 (d, J=8.7 Hz, 2 H), 7.40 (d, 4.2 Hz, 1 H), 7.11 (d, J=9 Hz, 4 H), 6.88 (m, 6 H), 4.59 (m, 4 H), 3.82 (s, 6 H), 1.33 ppm (m, 6 H);13C NMR (75 MHz, CDCl3):
d=178.7, 163.1, 161.3, 159.9, 156.8, 150.8, 149.3, 148.1, 139.5, 135.5, 127.8, 127.4, 124.1, 123.4, 118.8, 114.9, 108.7, 55.5, 43.9, 43.1, 12.5, 12.4 ppm; IR (neat): n˜=1655 (C=O), 1236 cm 1 (C=S); MS (MALDI-TOF): m/z: 597.2 [M+]; HRMS (MALDI-TOF): m/z: calcd:
597.1750(5) [M+·]; found: 597.1743 (1.25 ppm); HRMS (FAB): m/z:
calcd: 597.1750(5) [M+·]; found: 597.1768 (2.93 ppm).
5-({5’-[Bis(4-methoxyphenyl)amino]-[2,2’-bithiophen]-5-yl}methy- lene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione (TT-TBB): TT-CHO (140 mg, 0.33 mmol) was dissolved in a solution of diethylthiobarbituric acid (76 mg, 0.38 mmol) in dry CHCl3
(25 mL). Then three drops of triethylamine were added and the re- sulting solution was stirred at room temperature. After 24 h, the re- action mixture was diluted with CH2Cl2, and washed with a solution of sodium hydroxide (1m), water, and brine. After removal of the solvent the residue was subjected to chromatography on silica gel using dichloromethane as eluent to afford a dark blue solid (121 mg, 61 %). M.p. 176–1808C;1H NMR (300 MHz, C6D6):d=8.53 (s, 1 H), 7.04 (d, J=9 Hz, 4 H), 6.97 (d,J=4.2 Hz, 1 H), 6.87 (d, J=
4.5 Hz, 1 H), 6.66 (d,J=9 Hz, 4 H), 6.60 (d,J=4.2 Hz, 1 H), 6.12 (d, J=4.2 Hz, 1 H), 4.55 (m, 4 H), 3.25 (s, 6 H), 1.32 ppm (m, 6 H);
13C NMR (75 MHz, CDCl3): d=178.6, 161.4, 160.2, 160.1, 157.6, 157.5, 148.3, 148.2, 139.6, 134.3, 129.1, 126.5, 122.8, 122.7, 114.9, 112.3, 107.1, 55.5, 43.8, 42.9, 12.5, 12.4 ppm; IR (neat):n˜=1644 (C=
O), 1242 cm 1(C=S); HRMS (MALDI-TOF):m/z: calcd: 603.1314 [M+
·]; found: 603.1299 (2.5 ppm).
2-[(5-{4-[Bis(4-methoxyphenyl)amino]phenyl}thiophen-2-yl)- methylene]-1H-indene-1,3(2H)-dione (PT-I): PT-CHO (0.208 g, 0.5 mmol) was dissolved in a solution of indanedione (72 mg, 0.5 mmol) in dry CHCl3(50 mL). Then three drops of triethylamine were added and the resulting solution was stirred at room temper- ature. After 24 h, the reaction mixture was diluted with CH2Cl2, and washed with a solution of sodium hydroxide (1m), water, and brine. After removal of solvent the residue was subjected to chro- matography on silica gel using dichloromethane/pentane (4:1) as eluent and then reprecipitated in pentane to afford a green solid (139 mg, 51 %). Monocrystals were obtained by slow evaporation of a solution of chloroform/pentane (1:1). M.p. 194–1988C;1H NMR (300 MHz, C6D6): d=7.99 (s, 1 H), 7.73 (m, 2 H), 7.48 (d, J=3.9 Hz, 1 H), 7.03 (d,J=9 Hz, 4 H), 6.97 (m, 2 H) 6.91 (d,J=9 Hz, 2 H), 6.84 (d,J=3.9 Hz, 1 H), 6.74 (d,J=9 Hz, 4 H), 3.29 ppm (s, 6 H);13C NMR (125 MHz, CDCl3): d=190.7, 189.8, 156.5, 144.2 (2 C), 141.9, 140.4, 136.3, 135.3, 134.8, 134.6, 127.4, 127.7, 127.3, 123.3 (2 C), 122.8, 122.6, 119.1 (2 C), 114.8 (2 C), 55.5 ppm; IR (neat):n˜=1673 cm 1(C=
O); MS (MALDI-TOF): m/z: 543.1 [M+]; HRMS (MALDI-TOF): m/z:
calcd: 543.1498 [M+·]; found: 543.1490 (1.5 ppm); MS (FAB):m/z:
calcd: 543.1498 [M+·]; found: 543.1498 (0 ppm); X-ray structure: tri- clinic,P 1.
2-({5’-[Bis(4-methoxyphenyl)amino]-[2,2’-bithiophen]-5-yl}methy- lene)-1H-indene-1,3(2H)-dione (TT-I): TT-CHO (0.118 g, 0.28 mmol) was dissolved in a solution of indanedione (41 mg, 0.28 mmol) in dry CHCl3(50 mL). Then three drops of triethylamine were added and the resulting solution was stirred at room temperature. After 24 h, the reaction mixture was diluted with CH2Cl2, and washed with a solution of sodium hydroxide (1m), water, and brine. After removal of solvent the residue was subjected to chromatography on silica gel using dichloromethane/pentane (4:1) as eluent and then precipitated in pentane to afford a dark blue solid (85 mg,
55 %). M.p. 151–1558C; 1H NMR (300 MHz, C6D6): d=7.91 (s, 1 H), 7.72 (m, 2 H) 7.07 (d,J=9 Hz, 4 H), 6.97 (m, 2 H), 6.92 (d,J=3.9 Hz, 1 H), 6.69 (d, J=9 Hz, 4 H), 6.60 (d, J=4.2 Hz, 1 H), 6.18 (d, J=
3.9 Hz, 1 H), 3.26 ppm (s, 6 H). The missing thiophenic proton was under the solvent signal; 13C NMR (125 MHz, CDCl3): d=190.7, 189.9, 157.1, 152.9, 144.6, 141.9, 140.4, 139.9, 135.9, 134.6, 134.4, 134.1, 130.9, 128.8, 127.3, 126.2, 123.5, 122.6, 122.5, 122.4, 114.8, 112.7, 55.5 ppm; IR (neat):n˜=1667 cm 1(C=O); MS (MALDI-TOF):
m/z: 549.1 [M+]; HRMS (MALDI-TOF): m/z: calcd: 549.1063 [M+·];
found: 549.1061 (0.36 ppm); MS (FAB):m/z: calcd: 549.1063 [M+·];
found: 549.1055 (1.46 ppm).
(Z)-2-{2-[(5-{4-[Bis(4-methoxyphenyl)amino]phenyl}thiophen-2- yl)methylene]-3-oxo-2,3-dihydro-1H-inden-1-ylidene}malononi- trile (PT-ICN): PT-CHO (80 mg, 0.19 mmol) was dissolved at 608C in ethanol (10 mL). Then, 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)ma- lononitrile (45 mg, 0.23 mmol) was added in portions and the re- sulting mixture was stirred at 608C for 1 h. After cooling, a new precipitate appeared in the solution. The solid was removed by fil- tration and then purified by column chromatography on silica gel (eluent: dichloromethane) to afford a dark blue solid (79 mg, 71 %).
M.p. 155–1608C; 1H NMR (300 MHz, CDCl3+Et3N):d=8.82 (s, 1 H), 8.66 (m, 1 H), 7.88 (m, 1 H), 7.80 (d, J=4.2 Hz, 1 H), 7.72 (m, 2 H), 7.59 (d,J=9 Hz, 2 H), 7.35 (d,J=4.2 Hz, 1 H), 7.12 (d,J=9 Hz, 4 H), 6.88 (m, 6 H), 3.82 ppm (s, 6 H); 13C NMR (125 MHz, CDCl3): d= 188.3, 160.7 (2 C), 147.0 (2 C), 139.9, 138.8, 137.9 (2 C), 136.8, 134.8, 134.2, 128.2, 127.6 (2C), 127.5, 125.1 (2 C), 123.5, 121.1, 114.9, 114.8, 114.7, 114.6, 68.5, 55.5 ppm; IR (neat):n˜=2220 (CN), 1589 cm 1 (C=O); MS (MALDI-TOF):m/z: 591.3 [M+]; HRMS (FAB):m/z: calcd:
591.1616 [M+]; found: 591.1602 (2.37 ppm).
(Z)-2-[2-({5’-[Bis(4-methoxyphenyl)amino]-[2,2’-bithiophen]-5-yl}- methylene)-3-oxo-2,3-dihydro-1H-inden-1-ylidene]malononitrile (TT-ICN): TT-CHO (120 mg, 0.28 mmol) was dissolved at 608C in ethanol (10 mL). Then, 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)ma- lononitrile (66 mg, 0.34 mmol) was added in portions and the re- sulting mixture was stirred at 608C for 1 h. After cooling, a new precipitate appears in the solution. The solid was removed from
&by&filtration and then purified by column chromatography on
silica gel (eluent: dichloromethane) to afford a dark green solid (106 mg, 62 %). M.p. 231–2358C;1H NMR (300 MHz, CDCl3):d=8.78 (s, 1 H), 8.61 (m, 1 H), 7.83 (m, 1 H), 7.68 (m, 2 H), 7.63 (d,J=3.9 Hz, 1 H), 7.32 (d, J=4.2 Hz, 1 H), 7.22 (d, J=9 Hz, 4 H), 7.02 (m, 1 H), 6.90 (d, 4 H, J=9 Hz), 6.26 (m, 1 H), 3.84 ppm (s, 6 H); 13C NMR (125 MHz, CDCl3):d=188.5, 160.6, 160.5, 157.6, 147.4, 139.9, 139.3, 136.9, 136.7, 134.5, 133.9, 129.3, 129.2(5), 129.2, 126.6, 124.9, 124.3, 123.2, 122.7, 115.2, 115.1, 114.8, 114.6, 112.0, 66.9, 55.5 ppm; IR (neat): n˜=2212 (CN), 1587 cm 1 (C=O); MS (MALDI-TOF): m/z:
597.1 [M+]; HRMS (MALDI-TOF):m/z: calcd: 597.1175 [M+·]; found:
597.1168 (1.2 ppm).
2,2’-{2-[(5-{4-[Bis(4-methoxyphenyl)amino]phenyl}thiophen-2-yl)- methylene]-1H-indene-1,3(2H)-diylidene}dimalononitrile (PT- I2CN): PT-CHO (80 mg, 0.24 mmol) was dissolved at 908C in acetic anhydride (10 mL). Then, 2,2’-(1H-indene-1,3(2H)-diylidene)dimalo- nonitrile (60 mg, 0.25 mmol) was added in portions and the result- ing mixture was stirred at 908C for 1 h. After cooling, a precipitate appeared in the solution. The solid was removed by filtration and then purified by column chromatography on silica gel (eluent: di- chloromethane) to afford a dark green solid (98 mg, 64 %). M.p.
159–1648C;1H NMR (300 MHz, C6D6):d=8.37 (s, 1 H), 8.23 (m, 2 H), 7.19 (d, J=9 Hz, 2 H), 7.04 (d, J=8.7 Hz, 4 H), 6.91 (d, J=4.2 Hz, 1 H), 6.89 (d, J=9 Hz, 2 H), 6.74 (m, 6 H), 6.65 (d, J=4.5 Hz, 1 H), 3.29 ppm (s, 6 H);13C NMR (125 MHz, CDCl3):d=160.9, 159.0, 157.0, 151.2, 139.1, 137.3, 136.2, 134.8, 134.4, 127.9, 127.5, 125.5, 125.4,
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123.7, 123.1, 118.7, 114.9, 113.7, 113.6, 72.6, 55.6 ppm; IR (neat):n˜= 2217 cm 1(CN); HRMS (MALDI-TOF):m/z: calcd: 639.1723(5) [M+
·]; found: 639.1718 (0.9 ppm).
Acknowledgements
V.J. thanks the French minister of research for a grant, and An- toine Lelige and Thodulf Rousseau for their help with OSC fab- rication. The authors thank the Johnson–Matthey Company for their generous gift of palladium catalysts.
Keywords: chromophores · donor–acceptor systems · heterocycles · semiconductors · structure–property relationships
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Received: November 9, 2014 Published online on&& &&, 0000
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V. Jeux, O. Segut,* D. Demeter, O. AlvÞque, P. Leriche,* J. Roncali*
&&–&&
Push–Pull Triphenylamine Chromophore Syntheses and Optoelectronic Characterizations
Give and take: Nine chromophores based on a dianisylamino donor group and various electron acceptors connect- ed by means of two types ofp-conju- gating spacers have been synthesized and characterized (see figure). The elec- tronic properties of these molecules can be modulated by varying the strength of the acceptor group and/or the struc- ture of the conjugating spacer.
