A structural study of Troger's base scaffold-based dyes for DSSC applications

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A structural study of Troger’s base scaffold-based dyes for DSSC applications

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Simona Urnikaite , Titas Braukyla , Artiom Magomedov , Egidijus Kamarauskas , Tadas Malinauskas ,

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and Vytautas Getautis *

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Department of Organic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, LT-50254,

Kaunas, Lithuania

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Department of Solid State Electronics, Vilnius University, Sauletekio 9, Vilnius, 10222, Lithuania.

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Abstract

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Three Troger’s base scaffold-based metal-free sensitizers TD1, TD2 and TD3 with triphenylamine donor

and rhodanine-3-acetic acid as an acceptor/anchoring group were designed and synthesized for dye-

sensitized solar cells. The sensitizer series was designed to investigate the influence of the poly[n]enic

(from n = 0 to 2) backbones and their anchoring effect in DSSCs. Optical, electrochemical and

photovoltaic properties were compared with analogues dyes D1-D3 possessing one anchoring group. It

has been proven that the extended polymethine chains ensure flexibility of these units and inspire the

interaction between two chromophores promoting aggregate formation in these Troger’s base-based dyes.

Keywords

Dye-Sensitized Solar Cells; Polymethine Dyes; Troger’s Base; Anchoring Group; Titanium Dioxide.

1. Introduction

Among the emerging photovoltaic technologies, dye-sensitized solar cells (DSSCs) have attracted

significant attention as one of the promising energy harvesting devices since the report of Ru-based

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photosensitizers [1]. After two decades of research and development, DSSCs with iodide/triiodide (I /I )

liquid electrolyte have achieved record power conversion efficiency (PCE) over 13% based on Zn-

porphyrin complex dyes [2,3]. Compared with them, metal-free organic dyes have such advantages as

relatively lower production cost, facile synthetic methodologies and high molar extinction coefficient [4].

An impressive cell efficiency of 12.5% achieved by a novel metal-free alkoxysilyl carbazole dye

ADEKA-1 (Fig. 1) demonstrated that metal-free dyes could be promising sensitizers for realizing highly

efficient DSSCs [5]. Towards the realization of higher photovoltaic performance and durability in

DSSCs, the development of the sensitizing dyes is one of the most important approaches.

It is well known that most of the excellent sensitizers have the donor-π-acceptor (D-π-A) structures

which facilitate effective photoinduced intramolecular charge transfer across the molecule [6]. However,

the single 1D-π-1A sensitizer often has a rod-shaped structure, which may cause undesirable dye

aggregation and charge recombination [7]. To enhance the photovoltaic performance in DSSCs,

considerable efforts have been devoted to optimize the structure of the organic dyes, such as increasing

the amount of anchoring groups and/or extending π-conjugation to increase the molar extinction

coefficient of the absorption band, which can improve the light harvesting ability of the dyes [4a,8]. The

dye containing double/multiple anchor groups exhibited a unique advantage of stronger bonding with the

TiO surface. Strong binding not only improves adsorption but also leads to red shift in absorption,

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efficient charge injection [4a,9] and photocurrent generation [4a,10].

For an efficient dye, choosing an appropriate anchoring group moiety is particularly important. For

example, di-anchoring N719 dye gives higher cell efficiency than the protonated N3 dye with quadri-

anchoring groups (Fig. 1), which is attributed to the effect of the bound dye on the energy of the TiO₂

conducting band [11]. In recent years, the importance of anchoring groups for photovoltaic applications

was investigated by several research groups. Jia and Zheng reported that the PCE of the DSSC based on

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Y-shaped D-π-(A)

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type phenthiozine dye ZJA2 (4.55%) was 67% higher than the DSSC based on single

1D-π-1A sensitizer ZJA1 (2.72%, Fig. 1) [7]. Designed DSSCs of Abbotto et al. yielded power

conversion efficiency up to 5.7% (4.9% with ionic liquid electrolyte) with increased photocurrent and

enhanced stability under 1 sun conditions caused by the di-anchoring groups [12]. Sirohi and Lee

concluded that the di-anchoring moiety in dye KS-5 caused strong binding to TiO which forced the dye

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molecule to assume a non-planar conformation, thereby minimizing aggregation [13]. This factor together

with an extended conjugated framework led to about 1.5 times higher efficiency of KS-5 compared to

parent dye L1 (Fig. 1). Recently Cao et al., reported the novel metal-free organic dye bearing two

symmetric double donor-acceptor segments with an impressive power conversion efficiency, which is

22% higher than that of the mono-anchoring dye based counterpart [4a]. However, the same scientific

group obtained lower photovoltaic performance of di-anchoring phenothiazine based dye DP-2 compared

to its counterpart mono-anchoring dye SP (Fig. 1) [14]. This new dye featuring A-D-π-D-A configuration

with extended conjugation showed a higher molar extinction coefficient (ε), but exhibited π-stacked

aggregation on the TiO surface, resulting in low efficiency of electron injection.

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Insert Figure 1

In our previous work [15], we presented a novel A-π-D-π-A metal-free organic dye D7 (Fig. 1) with

two anchoring groups for solid state DSSC (ssDSSC) with spiro-OMeTAD as hole transporting material

(HTM). As one would expect, D7 demonstrated the highest extinction coefficient of all investigated D-π-

A hydrazone dyes in that study, mostly due to the presence of two electron accepting units and larger

change in the electronic charge distribution occurring during excitation. The device based on the

sensitizer D7 had the strongest and widest light absorbance from the whole series. However, the external

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quantum efficiency and ssDSSC performance decreased more than 50% compared with analogues

sensitizers possessing one anchoring group. We concluded that the D-(π-A) molecule has a rod-shaped

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structure, which might cause undesirable dye aggregation promoted by carboxylic acid moieties not

attached to the TiO surface. The unbound anchoring group could serve as a charge recombination in site

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between the HTM and dye layers, reducing the performance on the ssDSSC cell.

In the current work, we synthesized three Troger’s base (TB) scaffold-based metal-free sensitizers

TD1, TD2 and TD3 (Fig. 2) with a triphenylamine donor group and rhodanine-3-acetic acid unit as the

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acceptor/anchoring group to investigate their di-anchoring effect in DSSCs. TB being a V-shaped C -

symmetric chiral molecule possesses many interesting features. TB analogues have found applications as

building blocks in the fields of supramolecular chemistry [16], molecular recognition [17], catalysis,

enzyme inhibitors [18], also as a central linking unit in the synthesis of HTMs [19]. The TB structure

allows it to be used as a core and provide angle (~ 90º) orientation for the conjugated π systems conjoined

to it [20]. The non-planar structure of the TB and presence of two carboxyl groups should ensure two

separate channels for charge transfer to TiO and increase in overall device efficiency. Analogues dyes

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D1, D2 and D3 (Fig. 1) with one anchoring group were synthesized for comparison.

Insert Figure 2

2. Experimental details

2.1 General

The solvents (tetrahydrofuran (THF), 1,4-dioxane, dimethyl sulfoxide (DMSO) and toluene) were dried

by standard procedures. Other reagents were purchased from Aldrich and TCI Europe and used without

further purification. 2-(4-Bromophenyl)-5,5-dimethyl-1,3-dioxane (14) [21] and 2,8-dibromo-4,10-

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dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine [22] were synthesized according to the earlier

reported procedures. Reactions which required the use of anhydrous, inert-atmosphere techniques were

carried out under inert atmosphere (argon). Reactions were monitored by using TLC on ALUGRAM SIL

G/UV254 plates and chromatographic separations were performed with silica gel (grade 9385, 230−400

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mesh, 60 Å, Aldrich). H (400 MHz) and C (100 MHz) NMR spectra were recorded at room

temperature with a Bruker Avance III 400 spectrometer. The chemical shifts, expressed in ppm, were

relative to tetramethylsilane (TMS). Infrared spectra were recorded on a Perkin Elmer Spectrum One

spectrometer using KBr pellets. UV-Vis spectra were recorded on Perkin Elmer Lambda 35 UV/Vis

spectrometer. Fluorescence (FL) of the investigated compounds in dilute DMSO solutions was measured

using an Edinburgh Instruments Fluorescence Spectrometer FLS920. Melting points were determined

using an electrothermal MEL-TEMP capillary melting point apparatus. Elemental analysis (C, H, and N)

was done using Exeter Analytical CE-440 elemental analyser, Model 440 C/H/N/.

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2.2 Cyclic-Voltammetry Measurements

The electrochemical studies were carried out by a three-electrode assembly cell from Bio-Logic SAS

potentiostat-galvanostat. The measurements were carried out with a glassy carbon electrode in THF

solutions containing 0.1 M tetrabutylammonium hexafluorophosphate as electrolyte, Pt as the reference

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and counter electrodes at a scan rate of 50 mV s . Each measurement was calibrated with ferrocene (Fc).

2.3 Ionization Potential Measurements

The ionization potential I of the layers of the synthesized compounds was measured by the electron

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photoemission in air method [23,24]. The samples for the ionization potential measurement were

prepared by dissolving materials in CHCl and were coated on Al plates precoated with a ~0.5 µm thick

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methylmethacrylate and methacrylic acid copolymer adhesive layer. The thickness of the transporting

material layer was 0.5‒1 µm. Usually the photoemission experiments are carried out in vacuum and high

vacuum is one of the main requirements for these measurements. If the vacuum is not high enough, the

sample surface oxidation and gas adsorption influence the measurement results. In our case, however, the

organic materials investigated are stable enough to oxygen and the measurements may be carried out in

air. The samples were illuminated with monochromatic light from a quartz monochromator with

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deuterium lamp. The power of the incident light beam was (2‒5)⋅10 W. A negative voltage of –300 V

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was supplied to the sample substrate. The counter-electrode with a 4.5×15 mm slit for illumination was

placed at 8 mm distance from the sample surface. The counter-electrode was connected to the input of the

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BK2‒16 type electrometer, working in the open input regime, for the photocurrent measurement. A 10

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– 10 A strong photocurrent was flowing in the circuit under illumination. The photocurrent I is strongly

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dependent on the incident light photon energy hν. The I =f(hν) dependence was plotted. Usually the

dependence of the photocurrent on incident light quanta energy is well described by a linear relationship

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between I and hν near the threshold. The linear part of this dependence was extrapolated to the hν axis

and the I value was determined as the photon energy at the interception point.

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2.4 Computational Details

The theoretical calculations were performed using TURBOMOLE version 7.0 software [25a]. The

molecular structure of the investigated compounds was optimized using Becke’s three parameter

functional, B3LYP [25b,c] and the def2-SVP [25d,e] basis set in vacuum. Optimized structures and the

molecular orbitals were visualized with TmoleX version 4.1 software [25f].

2.5 Solar cell assembly

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photo-electrodes were prepared on fluorine-doped tin oxide (FTO) glass, which initially was

cleaned in ultrasonic bath with detergent, water, acetone and ethanol for 30 min respectively. Then a

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screen printing technique was used to prepare mesoporous TiO films with an area of 5 × 5 mm . The

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film consists of one transparent layer (8 µm) which was printed with colloidal TiO paste (Dyenamo

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GPS-30TS) and one 4 µm light-scattering layer (Dyenamo paste DN-GPS-22OS). Before printing the

second layer the film was dried at 125 ˚C for 6 min. Afterwards the electrodes were sintered in an oven

(Nabertherm Controller P320) in an air atmosphere using a temperature gradient program with four levels

at 180 ˚C (15 min), 320 ˚C (15 min), 390 ˚C (15 min) and 500 ˚C (30 min). Prior to the dye-sensitization

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the electrodes were post treated with 40 mM TiCl solution for 30 min, followed by heating at 500 ˚C for

30 min. At a temperature of 90 ˚C the electrodes were immersed in a dye bath for 18 h containing either

D1 (0.5 mM), D2 (0.5 mM), D3 (0.5 mM) in DCM and TD1 (0.5 mM), TD2 (0.5 mM), TD3 (0.5 mM) in

DCM:MeOH (4:1 v/v), or N719 (0.3 mM) and D35 (0.2 mM) in tert-butanol: acetonitrile (1:1 v/v). Any

non-attached dye was removed with solvent used for the dye bath. Counter electrodes were prepared by

depositing 10 ꢀL of a H PtCl solution in ethanol (5 mM) to FTO glass substrates followed by heating in

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air at 400 ˚C for 30 min. Solar cells were assembled by sandwiching the photoelectrode and the counter

electrode using a 25 ꢀm thick thermoplastic Surlyn frame. An electrolyte solution was then injected

through a hole predrilled in the counter electrode by vacuum back filling and the cell was sealed with

thermoplastic Surlyn cover and a microscope glass coverslip. The electrolyte consists of LiI (0.1 M), I₂

(0.05 M), 1-butyl-3-methylimidazolium iodide (BMII, 0.6 M) and 4-tert butylpyridine (TBP, 0.5 M) in

acetonitrile. Three solar cells were made with every dye.

2.6 Solar cells characterization

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Current-voltage (IV) characteristics were determined by using a combination of a source measurement

unit (Keithley 2400) and a solar simulator (Newport, model 91160). The solar simulator provided light

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with AM 1.5 G spectral distribution and was calibrated to an intensity of 100 mW cm using a certified

reference solar cell (Fraunhofer ISE). On top of the DSC a black metal mask with an aperture of 5 × 5

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mm was applied.

Incident photon-to-current conversion efficiency (IPCE) spectra were measured with a computer-

controlled setup comprising a xenon light source (Spectral Products ASB-XE-175), a monochromator

(Spectral Products CM110) and a Keithley multimeter (model 2700). The IPCE spectra were calibrated

using a certified reference solar cell (Fraunhofer ISE).

2.7 Synthesis of dyes

General procedure A: To a solution of the mixture of respective aldehyde (1 mmol) and tributyl(1,3-

dioxalan-2-ylmethyl)phosphonium bromide (1.1 mmol) in anhydrous tetrahydrofuran (3 mL) was added

sodium hydride (60% dispersed in mineral oil, 3.0 equiv.) under argon gas atmosphere, and the resulting

turbid solution was stirred at room temperature for 12 hours. The reaction was monitored by TLC (3:1:21

v/v ethyl acetate/toluene/n-hexane). After completion of the reaction, the excess NaH was quenched

using 10% aq. HCl solution under cooling and the reaction mixture was brought to acidic pH. The

reaction mixture was then stirred further more at room temperature for 1 hour. The mixture was poured

into distilled water (10 mL) and extracted with ethyl acetate. The organic layer was dried over anhydrous

Na SO , filtered off, and the solvent evaporated. The crude product was purified by column

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chromatography [26].

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General procedure B: To a solution of respective aryl aldehyde (1 mmol) in benzene (2 mL) were added

2,2-dimethyl-1,3-propanediol (1.2 mmol) and p-toluenesulfonic acid monohydrate (0.11 mmol). The

resulting mixture was stirred at 80 ⁰C for 3 hours. After cooling to room temperature, the reaction was

quenched by adding distilled water, and then was extracted with ethyl acetate. The organic layer was

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dried over anhydrous Na SO , filtered, and the solvent evaporated. The crude product was purified by

column chromatography [21].

General procedure C: Mixture of dioxane (2 mL) and water (4%) was purged with argon for 20 minutes.

Palladium(II) acetate (0.5%) and 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPhos) (1.5%) were

added and mixture was heated to 80 ⁰C for 2 min. Respective aryl halide (1 mmol), 3,4-dimethylaniline

(1.2 mmol) and sodium tert-butoxide (1.4 mmol) were added and the solution was refluxed for the

indicated time (30 min – 2 h) under Ar atmosphere. After termination of the reaction (TLC control), the

mixture was filtered through celite, distilled water were added and extraction was done with ethyl acetate.

The organic layer was dried over anhydrous Na SO , filtered, and the solvent evaporated. The crude

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product was purified by column chromatography.

General procedure D: A solution of 2,8-dibromo-4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]-

diazocine (1 mmol), respective amine (2.5 mmol) and anhydrous toluene (10 mL) was purged with argon

for 30 minutes. Afterwards, palladium(II) acetate (2%), tri-tert-butylphosphonium tetrafluoroborate

(2.7% mmol) and sodium tert-butoxide (3 mmol) were added and the solution was heated to reflux under

Ar atmosphere. After termination of the reaction (TLC control), the mixture was filtered through celite,

distilled water was added and extraction was done with ethyl acetate. The organic layer was dried over

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anhydrous Na

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, filtered, and the solvent evaporated. The crude product was purified by column

chromatography.

General procedure E: A solution of respective protected aldehyde (1 mmol) in THF (3 mL) and 10% aq.

HCl solution (to acidic pH) was stirred at 40 ⁰C for 1 hour. The solution was poured into saturated

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NaHCO solution and extracted with ethyl acetate. The combined organic phases were washed with brine,

dried with Na SO , and concentrated in vacuo. The crude residue was purified by column

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chromatography.

General procedure F: The mixture of respective aldehyde (1 mmol), rhodanine-3-acetic acid (1.2–2.4

mmol) and ammonium acetate (0.3 mmol) was refluxed in either anhydrous toluene (26 mL) or glacial

acetic acid (3 mL). At the end of the reaction (TLC control), the mixture was cooled to room temperature.

The obtained crystals which formed upon standing were filtered off and washed or the crude product was

purified by column chromatography.

E-3-(4-Bromophenyl)-2-propenal (1)

Following general procedure A, a mixture of 4-bromobenzaldehyde (2 g, 10.8 mmol), tributyl(1,3-

dioxalan-2-ylmethyl)phosphonium bromide (4.39 g, 11.89 mmol) and NaH in anhydrous THF (30 mL)

was stirred at room temperature for 12 h. Product was purified by column chromatography using 3:1:21

v/v ethyl acetate/toluene/n-hexane as an eluent. Aldehyde 1 was obtained as light yellow crystals. Yield:

2.1 g (92%).

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H NMR (400 MHz, CDCl , ppm) δ 9.71 (d, J = 7.6 Hz, 1H), 7.60–7.54 (m, 2H), 7.49–7.37 (m, 3H),

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6.71 (dd, J = 16.0, 7.6 Hz, 1H).

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C NMR (101 MHz, CDCl , ppm) δ 193.46, 151.19, 132.86, 132.39, 129.79, 128.98, 125.70.

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Anal. calcd. for C H BrO: C, 51.22; H, 3.34. Found: C, 51.23; H, 3.22.

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(2E,4E)-5-(4-bromophenyl)penta-2,4-dienal (2)

Prepared from the aldehyde 1 (0.31 g, 1.48 mmol) in anhydrous THF (3.5 mL) following general

procedure A (tributyl(1,3-dioxalan-2-ylmethyl)phosphonium bromide: 0.60 g, 1.63 mmol). Reaction

mixture was refluxed for 5 h. The crude product was purified by column chromatography using 3:1:21

v/v ethyl acetate/toluene/n-hexane as an eluent to collect aldehyde 2 as light yellow crystals. Yield: 0.26 g

(73 %). The obtained data of product are in good agreement with reported data [27].

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H NMR (400 MHz, CDCl , ppm) δ 9.64 (d, J = 7.9 Hz, 1H), 7.53 (d, J = 8.5 Hz, 2H), 7.38 (d, J = 8.5

Hz, 2H), 7.32–7.20 (m, 1H), 7.07–6.91 (m, 2H), 6.30 (dd, J = 15.2, 7.9 Hz, 1H).

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C NMR (101 MHz, CDCl , ppm) δ 193.57, 151.54, 140.91, 134.50, 132.17, 132.07, 128.91, 126.81,

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123.79.

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Anal. calcd. for C11H BrO: C, 55.72; H, 3.83. Found: C, 55.69; H, 3.80.

(E)-2-(4-bromostyryl)-5,5-dimethyl-1,3-dioxane (3)

Following general procedure B, a mixture of aldehyde 1 (1.79 g, 8.49 mmol), 2-dimethyl-1,3-propanediol

(1.06 g, 10.19 mmol) and p-toluenesulfonic acid monohydrate (0.17 g, 0.93 mmol) in benzene (17 mL)

was stirred at 80 ⁰C for 3.5 h. Product was purified by column chromatography using 3:1:21 v/v ethyl

acetate/toluene/n-hexane as an eluent to collect protected aldehyde 3 as whitish crystals. Yield: 2.0 g

(80%).

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H NMR (400 MHz, CDCl , ppm) δ 7.43 (d, J = 8.5 Hz, 2H), 7.26 (d, J = 8.5 Hz, 2H), 6.72 (d, J = 16.2

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Hz, 1H), 6.21 (dd, J = 16.2, 4.7 Hz, 1H), 5.02 (d, J = 4.2 Hz, 1H), 3.69 (d, J = 11.2 Hz, 2H), 3.55 (d, J =

10.8 Hz, 2H), 1.24 (s, 3H), 0.76 (s, 3H).

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C NMR (101 MHz, CDCl

23.01, 21.93.

Anal. calcd. for C H BrO : C, 56.58; H, 5.77. Found: C, 56.60; H, 5.74.

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, ppm) δ 135.08, 132.19, 131.70, 128.36, 126.39, 122.03, 100.57, 30.24,

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2-((1E,3E)-4-(4-bromophenyl)buta-1,3-dien-1-yl)-5,5-dimethyl-1,3-dioxane (4)

Following general procedure B, a mixture of aldehyde 2 (1.84 g, 7.76 mmol), 2-dimethyl-1,3-propanediol

(0.97 g, 9.31 mmol) and p-toluenesulfonic acid monohydrate (0.16 g, 0.85 mmol) in benzene (16 mL)

was stirred at 80 ⁰C for 3 h. Product was purified by column chromatography using 3:1:21 v/v ethyl

acetate/toluene/n-hexane as an eluent to collect protected aldehyde 4 as light yellow crystals. Yield: 1.6 g

(64%).

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H NMR (400 MHz, CDCl , ppm) δ 7.43 (d, J = 8.4 Hz, 2H), 7.25 (d, J = 7.6 Hz, 2H), 6.81‒6.68 (m,

1H), 6.62‒6.48 (m, 2H), 5.83 (dd, J = 15.3, 4.6 Hz, 1H), 4.96 (d, J = 4.6 Hz, 1H), 3.68 (d, J = 11.1 Hz,

2H), 3.53 (d, J = 10.8 Hz, 2H), 1.23 (s, 3H), 0.76 (s, 3H).

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C NMR (101 MHz, CDCl , ppm) δ 135.91, 133.23, 133.15, 131.74, 129.86, 128.47, 128.02, 121.59,

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100.37, 30.22, 22.99, 21.93.

Anal. calcd. for C16 : C, 59.45; H, 5.93. Found: C, 59.41; H, 5.89.

H19BrO

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N-(4-(5,5-dimethyl-1,3-dioxan-2-yl)phenyl)-3,4-dimethylaniline (5)

Compound 5 was synthesized following general method C: a mixture of Pd(OAc) (0.02 g, 0.09 mmol),

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SPhos (0.11g, 0.27 mmol), 2-(4-bromophenyl)-5,5-dimethyl-1,3-dioxane 14 (5 g, 18.44 mmol), 3,4-

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dimethylaniline (2.68 g, 22.13 mmol) and NaOt-Bu (2.48 g, 25.81 mmol) in anhydrous dioxane (35 mL)

was refluxed for 30 min. The crude product was purified by column chromatography using 0.5:14.5:10

v/v ethyl acetate/toluene/n-hexane and further purified by crystallization from 2-propanol to produce

diphenylamine 5 as white crystals. Yield: 4.62 g (80%).

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H NMR (400 MHz, CDCl₃_,_p_p_m) δ 7.36 (d, J = 8.5 Hz, 2H), 7.03–6.95 (m, 3H), 6.87 (d, J = 2.2 Hz, 1H),

6.82 (dd, J = 8.0, 2.4 Hz, 1H), 5.60 (s, 1H), 5.32 (s, 1H), 3.75 (d, J = 11.2 Hz, 2H), 3.63 (d, J = 10.6 Hz,

2H), 2.20 (s, 6H), 1.29 (s, 3H), 0.78 (s, 3H).

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C NMR (101 MHz, CDCl , ppm) δ 144.52, 140.53, 137.54, 130.47, 130.36, 129.76, 127.25, 120.33,

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116.65, 116.33, 101.92, 30.22, 23.11, 21.94, 19.96, 19.02.

Anal. calcd. for C20 : C, 77.14; H, 8.09; N, 4.50. Found: C, 77.03; H, 8.00; N, 4.52.

H25NO

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(E)-N-(4-(2-(5,5-dimethyl-1,3-dioxan-2-yl)vinyl)phenyl)-3,4-dimethylaniline (6)

Prepared from compound 3 (2.02 g, 6.81 mmol), 3,4-dimethylaniline (1.00 g, 8.17 mmol) in the mixture

2

of dioxane (15 mL) and water (4 %) applying the same procedure as for general procedure C ( Pd(OAc) :

0.007 g, 0.03 mmol; SPhos: 0.04 g, 0.10 mmol; NaOt-Bu: 0.92 g, 9.53 mmol). The resulting mixture was

stirred at reflux for 30 min. Product was separated by column chromatography using 3:1:21 v/v ethyl

acetate/toluene/n-hexane as an eluent and further purified by crystallization from 2-propanol to produce

diphenylamine 6 as pale yellow crystals. Yield: 1.60 g (70%).

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H NMR (400 MHz, CDCl , ppm) δ 7.27 (d, J = 8.6 Hz, 2H), 7.04 (d, J = 8.0 Hz, 1H), 6.94–6.84 (m,

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4H), 6.70 (d, J = 16.1 Hz, 1H), 6.08 (dd, J = 16.1, 5.1 Hz, 1H), 5.65 (s, 1H), 5.02 (d, J = 4.9 Hz, 1H),

3.69 (d, J = 11.2 Hz, 2H), 3.56 (d, J = 10.9 Hz, 2H), 2.22 (s, 3H), 2.21 (s, 3H), 1.25 (s, 3H), 0.76 (s, 3H).

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C NMR (101 MHz, CDCl , ppm) δ 144.20, 139.90, 137.63, 133.37, 130.37, 130.21, 128.05, 127.90,

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122.34, 120.95, 116.89, 116.06, 101.47, 30.23, 23.05, 21.99, 20.00, 19.08.

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27NO

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: C, 78.30; H, 8.06; N, 4.15. Found: C, 78.28; H, 8.06; N, 4.05.

N-(4-((1E,3E)-4-(5,5-dimethyl-1,3-dioxan-2-yl)buta-1,3-dien-1-yl)phenyl)-3,4-dimethylaniline (7)

Following general procedure C, a mixture of Pd(OAc) (0.005 g, 0.02 mmol), SPhos (0.03 g, 0.07 mmol),

2

protected aldehyde 4 (1.58 g, 4.90 mmol), 3,4-dimethylaniline (0.71 g, 5.89 mmol) and NaOt-Bu (0.66 g,

6.87 mmol) in dioxane (10 mL) and water (4%) was refluxed for 1 h under Ar atmosphere. Product was

purified by column chromatography using 3:1:21 v/v ethyl acetate/toluene/n-hexane as an eluent and

further purified by crystallization from 2-propanol to produce diphenylamine 7 as pale yellow crystals.

Yield: 1.23 g (69%).

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H NMR (400 MHz, CDCl , ppm) δ 7.28 (d, J = 8.6 Hz, 2H), 7.04 (d, J = 8.0 Hz, 1H), 6.93 (d, J = 8.6

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Hz, 2H), 6.91‒6.82 (m, 2H), 6.68‒6.49 (m, 3H), 5.77 (dd, J = 15.2, 4.9 Hz, 1H), 5.67(s, 1H), 4.95 (d, J =

5.1 Hz, 1H), 3.67 (d, J = 11.1 Hz, 2H), 3.53 (d, J = 10.9 Hz, 2H), 2.22 (s, 3H), 2.21 (s, 3H), 1.23 (s, 3H),

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0.75 (s, 3H). C NMR (101 MHz, CDCl , ppm) δ 143.84, 139.87, 137.60, 134.42, 134.19, 130.34,

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130.13, 128.84, 127.73, 127.35, 124.80, 120.71, 116.67, 116.30, 100.85, 30.17, 22.98, 21.93, 19.95,

19.03.

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Anal. calcd. for C24H29NO : C, 79.30; H, 8.04; N, 3.85. Found: C, 79.20; H, 8.08; N, 3.86.

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8

2

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(5S)-N ,N -bis(4-(5,5-dimethyl-1,3-dioxan-2-yl)phenyl)-N ,N -bis(3,4-dimethylphenyl)-4,10-dimethyl-

6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diamine (8)

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Following general procedure D, a mixture of diphenylamine 5 (2.18 g, 7.00 mmol), 2,8-dibromo-4,10-

dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (1.14 g, 2.80 mmol), Pd(OAc) (0.012 g, 0.05

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mmol), [P(t-Bu) H]BF (0.023 g, 0.07 mmol) and NaOt-Bu (0.81 g, 8.39 mmol) in anhydrous toluene (20

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mL) was heated at reflux for 2.5 h under Ar atmosphere. The crude product was purified by column

chromatography using 3:1:21 v/v ethyl acetate/toluene/n-hexane as an eluent to collect compound 8 as a

yellow solid. Yield: 1.8 g (76%).

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H NMR (400 MHz, CDCl , ppm) δ 7.32 (d, J = 8.5 Hz, 4H), 6.98 (d, J = 8.5 Hz, 6H), 6.86‒6.74 (m,

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6H), 6.48‒6.44 (m, 2H), 5.33 (s, 2H), 4.40 (d, J = 17.0 Hz, 2H), 4.27 (s, 2H), 3.82 (d, J = 17.0 Hz, 2H),

3.76 (d, J = 11.1 Hz, 4H), 3.63 (d, J = 10.9 Hz, 4H), 2.24 (s, 6H), 2.21 (s, 6H), 2.15 (s, 6H), 1.30 (s, 6H),

0.79 (s, 6H).

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C NMR (101 MHz, CDCl , ppm) δ 148.98, 145.48, 143.42, 141.19, 137.49, 133.78, 131.61, 131.33,

130.34, 129.07, 128.83, 128.27, 126.94, 126.11, 124.74, 122.93, 122.43, 119.66, 101.93, 77.77, 67.70,

54.99, 30.25, 23.13, 21.94, 19.87, 19.18, 17.03.

Anal. calcd. for C H N O : C, 78.77; H, 7.42; N, 6.45. Found: C, 78.78; H, 7.39; N, 6.45.

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(5S)-N ,N -bis(4-((E)-2-(5,5-dimethyl-1,3-dioxan-2-yl)vinyl)phenyl)-N ,N -bis(3,4-dimethylphenyl)-4,10-

dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diamine (9)

Prepared from the diphenylamine 6 (1.57 g, 4.67 mmol), 2,8-dibromo-4,10-dimethyl-6H,12H-5,11-

methanodibenzo[b,f][1,5]diazocine (0.76 g, 1.87 mmol) in the mixture of toluene (34 mL), Pd(OAc)

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(0.008 g, 0.04 mmol), [P(t-Bu) H]BF (0.015 g, 0.05 mmol) and NaOt-Bu (0.54 g, 5.60 mmol) applying

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the same procedure as for general procedure D. The resulting mixture was stirred at reflux for 1 h.

Product was purified by column chromatography using 3:1:21 v/v ethyl acetate/toluene/n-hexane as an

eluent to collect compound 9 as light yellow crystals. Yield: 1.37 g (80%).

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H NMR (400 MHz, CDCl , ppm) δ 7.28–7.12 (m, 9H), 7.02 (d, J = 8.1 Hz, 2H), 6.90–6.78 (m, 5H), 6.69

(d, J = 16.1 Hz, 2H), 6.49 (d, J = 2.3 Hz, 2H), 6.07 (dd, J = 16.1, 4.9 Hz, 2H), 5.01 (d, J = 4.7 Hz, 2H),

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4.44 (d, J = 17.0 Hz, 2H), 4.28 (s, 2H), 3.85 (d, J = 17.0 Hz, 2H), 3.69 (d, J = 11.1 Hz, 4H), 3.55 (d, J =

10.9 Hz, 4H), 2.25 (s, 6H), 2.22 (s, 6H), 2.17 (s, 6H), 1.24 (s, 6H), 0.76 (s, 6H).

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C NMR (101 MHz, CDCl , ppm) δ 148.32, 145.08, 143.01, 141.50, 137.63, 133.90, 133.06, 131.86,

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130.41, 128.88, 128.81, 127.54, 126.60, 125.23, 123.11, 122.92, 121.62, 120.16, 101.24, 67.57, 54.87,

30.18, 22.99, 21.94, 19.88, 19.20, 17.03.

Anal. calcd. for C61

H

68

N

4

O

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: C, 79.53; H, 7.44; N, 6.08. Found: C, 79.53; H, 7.40; N, 6.05.

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8

2

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(5S)-N ,N -bis(4-((1E,3E)-4-(5,5-dimethyl-1,3-dioxan-2-yl)buta-1,3-dien-1-yl)phenyl)-N ,N -bis(3,4-

dimethylphenyl)-4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diamine (10)

Following general procedure D, a mixture of diphenylamine 7 (1.20 g, 3.30 mmol), 2,8-dibromo-4,10-

dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (0.54 g, 1.32 mmol), Pd(OAc) (0.006 g, 0.03

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mmol), [P(t-Bu) H]BF (0.011 g, 0.03 mmol) and NaOt-Bu (0.38 g, 3.96 mmol) in anhydrous toluene (30

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mL) was heated at reflux for 3.5 h under Ar atmosphere. The crude product was purified by column

chromatography using 3:22 v/v acetone/n-hexane as an eluent to collect compound 10 as a yellow solid.

Yield: 1.4 g (45%).

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H NMR (400 MHz, CDCl ): δ = 7.25 (d, J = 8.6 Hz, 4H), 7.05 (d, J = 8.1 Hz, 2H), 6.96–6.30 (m, 11H),

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6.71–6.49 (m, 7H), 5.79 (dd, J = 15.0, 4.9 Hz, 2H), 4.98 (d, J = 4.9 Hz, 2H), 4.52 (d, J = 16.8 Hz, 2H),

4.38 (s, 2H), 3.90 (d, J = 17.0 Hz, 2H), 3.70 (d, J = 10.7 Hz, 4H), 3.56 (d, J = 11.0 Hz, 4H), 2.30 (s, 6H),

2.26 (s, 6H), 2.20 (s, 6H), 1.26 (s, 6H), 0.78 (s, 6H).

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C NMR (101 MHz, CDCl ): δ = 147.92, 144.96, 137.75, 134.23, 134.11, 133.98, 130.50, 127.81,

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127.35, 126.62, 125.70, 125.05, 122.95, 122.25, 100.82, 54.84, 30.22, 23.02, 21.97, 19.93, 19.25, 17.14.

Anal. calcd. for C65 : C, 80.21; H, 7.46; N, 5.76. Found: C, 80.15; H, 7.43; N, 5.71.

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4,4'-(((5S)-4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)bis((3,4-

dimethylphenyl)azanediyl))dibenzaldehyde (11)

Following general procedure E, product was purified by column chromatography using 1:4 v/v acetone/n-

hexane as an eluent to collect dialdehyde 11 as yellow crystals. Yield: 0.66 g (46%).

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H NMR (400 MHz, CDCl , ppm) δ 9.76 (s, 2H), 7.61 (d, J = 8.8 Hz, 4H), 7.11 (d, J = 8.0 Hz, 2H), 6.98–

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6.78 (m, 10H), 6.61 (d, J = 2.1 Hz, 2H), 4.50 (d, J = 17.0 Hz, 2H), 4.29 (s, 2H), 3.90 (d, J = 17.1 Hz, 2H),

2.32 (s, 6H), 2.26 (s, 6H), 2.22 (s, 6H).

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C NMR (101 MHz, CDCl , ppm) δ 190.32, 153.90, 143.49, 143.46, 141.46, 138.30, 134.71, 134.24,

131.32, 130.94, 129.39, 128.08, 128.02, 126.98, 124.40, 122.16, 117.78, 67.44, 54.78, 26.93, 19.91,

19.36, 17.11.

Anal. calcd. for C H N O : C, 81.00; H, 6.36; N, 8.04. Found: C, 81.02; H, 6.36; N, 8.00.

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(2E,2'E)-3,3'-((((5S)-4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)bis((3,4-

dimethylphenyl)azanediyl))bis(4,1-phenylene))diacrylaldehyde (12)

Following general procedure E, product was purified by column chromatography using 1:4 v/v acetone/n-

hexane as an eluent to collect dialdehyde 12 as yellow crystals. Yield: 0.86 g (78%).

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H NMR (400 MHz, CDCl , ppm) δ 9.61 (d, J = 7.8 Hz, 2H), 7.40–7.32 (m, 6H), 7.09 (d, J = 8.1 Hz,

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2H), 6.96‒6.92 (m, 2H), 6.90–6.84 (m, 8H), 6.60–6.50 (m, 4H), 4.49 (d, J = 17.0 Hz, 2H), 4.29 (s, 2H),

3.89 (d, J = 17.1 Hz, 2H), 2.30 (s, 6H), 2.26 (s, 6H), 2.21 (s, 6H).

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C NMR (101 MHz, CDCl , ppm) δ 193.78, 153.01, 151.36, 143.88, 142.83, 141.86, 138.11, 134.45,

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133.59, 130.76, 129.82, 129.21, 127.57, 126.42, 125.34, 125.30, 123.94, 121.53, 119.31, 67.45, 54.77,

19.91, 19.32, 17.09.

Anal. calcd. for C H N O : C, 81.79; H, 6.46; N, 7.48. Found: C, 87.78; H, 6.45; N, 7.50.

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(2E,2'E,4E,4'E)-5,5'-((((5S)-4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-

diyl)bis((3,4-dimethylphenyl)azanediyl))bis(4,1-phenylene))bis(penta-2,4-dienal) (13)

Following general procedure E, product was purified by column chromatography using 1:4 v/v THF/n-

hexane as an eluent to collect dialdehyde 13 as orange crystals. Yield: 0.8 g (70%).

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H NMR (400 MHz, CDCl , ppm) δ 9.57 (d, J = 8.0 Hz, 2H), 7.34‒7.18 (m, 5H), 7.06 (d, J = 8.1 Hz,

2H), 6.95–6.79 (m, 15H), 6.55 (d, J = 2.1 Hz, 2H), 6.20 (dd, J = 15.1, 8.0 Hz, 2H), 4.47 (d, J = 17.0 Hz,

2H), 4.29 (s, 2H), 3.87 (d, J = 16.7 Hz, 2H), 2.28 (s, 6H), 2.25 (s, 6H), 2.20 (s, 6H).

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C NMR (101 MHz, CDCl , ppm) δ 193.57, 153.00, 149.94, 144.38, 142.56, 142.38, 137.94, 134.27,

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132.96, 130.66, 130.04, 129.11, 128.61, 127.62, 127.21, 125.94, 123.57, 123.37, 120.96, 120.47, 114.15,

67.55, 54.88, 19.90, 19.28, 17.08.

Anal. calcd. for C H N O : C, 82.47; H, 6.54; N, 6.99. Found: C, 82.45; H, 6.56; N, 7.01.

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Dye TD1

Following general procedure F, a mixture of dialdehyde 11 (0.73 g, 1.05 mmol), rhodanine-3-acetic acid

(0.48 g, 2.52 mmol) and AcONH (0.05 g, 0.63 mmol) was refluxed in anhydrous toluene (3 mL) for 12

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h. The crude product was purified by column chromatography using 7:18 v/v acetone/n-hexane, 2:3 v/v

acetone/n-hexane and finally 3:22 v/v methanol/toluene to collect dye TD1 as a red solid. Yield: 0.37 g

-1

(34%), m.p. > 400°C. UV‒vis (DMSO): λmax (nm) 307 (ɛ = 36 382 M cm ), 475 (ɛ = 71 369 M cm ).

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H NMR (400 MHz, DMSO-d , ppm) δ 7.63 (s, 2H), 7.42 (d, J = 8.9 Hz, 4H), 7.15 (d, J = 8.2 Hz, 2H),

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7.00–6.83 (m, 6H), 6.75 (d, J = 8.9 Hz, 4H), 6.70–6.62 (m, 2H), 4.48–4.37 (m, 6H), 4.21 (s, 2H), 3.97 (d,

J = 17.6 Hz, 2H), 2.28 (s, 6H), 2.21 (s, 6H), 2.17 (s, 6H).

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C NMR (101 MHz, DMSO-d , ppm) 207.04, 193.22, 167.40, 167.33, 150.97, 143.68, 143.50, 141.12,

138.54, 134.81, 134.42, 133.40, 133.08, 131.45, 130.09, 128.14, 126.79, 124.77, 124.10, 122.39, 118.51,

117.73, 67.49, 54.50, 47.63, 31.16, 19.92, 19.38, 17.26.

-1

IR (KBr, cm ): ν = 3394 (OH); 3016 (aromatic CH); 2950, 2916, 2883 (aliphatic CH); 1698 (2×C=O);

1575 (C=C); 1505 (C-C); 1324 (C=S); 1200, 1181 (C-N).

Anal. calcd. for C H N O S : C, 65.62; H, 4.83; N, 8.06. Found: C, 65.60; H, 4.85; N, 8.06.

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Dye TD2

Following general procedure F, a mixture of dialdehyde 12 (0.29 g, 0.38 mmol), rhodanine-3-acetic acid

(0.18 g, 0.93 mmol) and AcONH (0.01 g, 0.11 mmol) was refluxed in anhydrous toluene (8 mL) for 12

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h. At the end of the reaction, the mixture was cooled to room temperature. Dark red crystals, formed

upon standing, were filtered off and washed with water (50 mL), toluene (50 mL) and finally with diethyl

ether (25 mL) to give dye TD2. Yield: 0.41 g (96%), m.p. 232-234 ⁰C. UV‒vis (DMSO): λ_m_a_x(nm) 298

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(ɛ = 56 510 M cm ), 510 (ɛ = 44 680 M cm ).

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H NMR (400 MHz, DMSO-d , ppm) δ 7.62–7.39 (m, 3H), 7.36–6.97 (m, 10H), 6.95–6.55 (m, 11H),

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4.65 (s, 2H), 4.54 (s, 4H), 4.40 (s, 4H), 2.25 (s, 6H), 2.20 (s, 6H), 2.16 (s, 6H).

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C NMR (101 MHz, DMSO-d , ppm) δ 203.31, 192.94, 174.26, 167.86, 167.80, 166.11, 152.26, 151.52,

150.49, 146.89, 144.09, 143.13, 143.02, 138.31, 137.82, 135.66, 131.32, 129.92, 129.37, 128.68, 127.65,

125.79, 119.60, 45.49, 36.41, 21.52, 19.92, 19.35, 17.26.

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IR (KBr, cm ): ν = 3430 (OH); 3033 (aromatic CH); 2966, 2922, 2850 (aliphatic CH); 1735 (2×C=O);

1600, 1563 (C=C); 1505 (C-C); 1327 (C=S); 1192, 1162 (C-N).

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Anal. calcd. for C61H N O S : C, 66.89; H, 4.97; N, 7.67. Found: C, 66.89, H, 4.95; N, 7.67.

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Following general procedure F, a mixture of dialdehyde 13 (0.25 g, 0.31 mmol), rhodanine-3-acetic acid

(0.14 g, 0.74 mmol) and AcONH (0.01 g, 0.10 mmol) was refluxed in anhydrous toluene (8 mL) for 12

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h. At the end of the reaction, the mixture was cooled to room temperature. Dark violet crystals, formed

upon standing, were filtered off and washed with water (50 mL), methanol (50 mL) and finally with

diethyl ether (25 mL) to give target dye TD3. Yield: 0.27 g (76%), m.p. > 400°C. UV‒vis (DMSO): λ_m_a_x

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(nm) 302 (ɛ = 43 360 M cm ), 389 (ɛ = 23 040 M cm ), 526 (ɛ = 68 550 M cm ).

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H NMR (400 MHz, DMSO-d , ppm) δ 7.51 (d, J = 11.9 Hz, 2H), 7.35 (d, J = 8.5 Hz, 4H), 7.28–7.12 (m,

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8H), 7.09 (d, J = 8.2 Hz, 2H), 6.93–6.64 (m, 8H), 6.56 (s, 2H), 6.51–6.39 (m, 2H), 4.61 (s, 4H), 4.38 (d, J

= 17.0 Hz, 2H), 4.18 (s, 2H), 3.90 (d, J = 17.4 Hz, 2H), 2.23 (s, 6H), 2.18 (s, 6H), 2.13 (s, 6H).

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C NMR (101 MHz, DMSO-d , ppm) δ 192.51, 174.28, 167.77, 166.05, 149.46, 147.93, 144.46, 142.66,

142.07, 140.42, 138.14, 137.75, 134.68, 134.43, 133.17, 131.23, 129.81, 129.37, 129.08, 128.67, 127.37,

126.19, 125.81, 121.45, 120.33, 54.53, 45.89, 21.52, 19.92, 19.31, 17.25.

-1

IR (KBr, cm ): ν = 3433 (OH); 3033 (aromatic CH); 2946, 2916 (aliphatic CH); 1698 (2×C=O); 1600,

1545 (C=C); 1502 (C-C); 1309 (C=S); 1197, 1154 (C-N).

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Anal. calcd. for C65H N O S : C, 68.04; H, 5.10; N, 7.32. Found: C, 68.00; H, 5.12; N, 7.34.

4-((3,4-dimethylphenyl)(m-tolyl)amino)benzaldehyde (15)

Aldehyde 15 was synthesized following general method C: a mixture of Pd(OAc) (0.009 g, 0.03 mmol),

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SPhos (0.04g, 0.09 mmol), diphenylamine 5 (2 g, 6.42 mmol), 3-iodotoluene (1 mL, 7.71 mmol) and

NaOt-Bu (0.86 g, 8.99 mmol) in anhydrous dioxane (12 mL) was refluxed for 2 h. The crude product

was purified by column chromatography using 0.5:24.5 v/v THF/n-hexane as an eluent to collect

intermediate as light brown oil. Subsequently, it was applied for general procedure E. A light yellow

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precipitate formed and was separated by extraction and concentration of the organic layer. Yield: 1.04 g

(55%).

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H NMR (400 MHz, CDCl , ppm) δ 9.77 (s, 1H), 7.64 (d, J = 8.8 Hz, 2H), 7.26‒7.18 (m, 1H), 7.10 (d, J

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= 8.1 Hz, 1H), 7.01‒6.85 (m, 7H), 2.30 (s, 3H), 2.26 (s, 3H), 2.21 (s, 3H).

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C NMR (101 MHz, CDCl , ppm) δ 190.41, 153.77, 146.08, 143.70, 139.65, 138.21, 133.99, 131.31,

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130.86, 129.46, 128.43, 127.86, 126.87, 125.91, 124.20, 123.40, 118.52, 21.40, 19.89, 19.33.

Anal. calcd. for C H NO: C, 83.78; H, 6.71; N, 4.44. Found: C, 83.73; H, 6.76; N, 4.45.

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(E)-3-(4-((3,4-dimethylphenyl)(m-tolyl)amino)phenyl)acrylaldehyde (16)

Aldehyde 16 was prepared from the arylaldehyde 15 (0.60 g, 1.91 mmol), in anhydrous THF (7 mL)

applying general procedure A (tributyl(1,3-dioxalan-2-ylmethyl)phosphonium bromide: 0.78 g, 2.10

mmol). Reaction mixture was stirred for 3 h. The crude product was purified by column chromatography

using 3:1:21 v/v ethyl acetate/toluene/n-hexane as an eluent to collect compound 16 as a yellow solid.

Yield: 0.51 g (78%).

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H NMR (400 MHz, CDCl , ppm) δ 9.64 (d, J = 7.8 Hz, 1H), 7.43‒7.36 (m, 3H), 7.31‒7.25 (m, 1H),

7.25‒7.16 (m, 2H), 7.12 (d, J = 8.0 Hz, 1H), 7.02‒6.88 (m, 5H), 6.60 (dd, J = 15.8, 7.8 Hz, 1H), 2.32 (s,

3H), 2.28 (s, 3H), 2.23 (s, 3H).

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C NMR (101 MHz, CDCl , ppm) δ 193.82, 153.03, 151.24, 146.51, 144.12, 139.48, 138.07, 133.39,

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130.74, 129.85, 129.32, 127.45, 126.25, 125.80, 125.53, 125.22, 123.79, 122.79, 120.13, 21.44, 19.93,

19.33.

Anal. calcd. for C H NO: C, 84.42; H, 6.79; N, 4.10. Found: C, 84.38; H, 6.76; N, 4.10.

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(2E,4E)-5-(4-((3,4-dimethylphenyl)(m-tolyl)amino)phenyl)penta-2,4-dienal (17)

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Compound 17 was prepared from the intermediate 16 (0.62 g, 1.81 mmol), in anhydrous THF (6 mL)

applying general method A (tributyl(1,3-dioxalan-2-ylmethyl)phosphonium bromide: 0.74 g, 1.99 mmol).

Reaction mixture was stirred for 1 h. The crude product was purified by column chromatography using

3:1:21 v/v ethyl acetate/toluene/n-hexane as an eluent to collect aldehyde 17 as a yellow solid. Yield:

0.56 g (84%).

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H NMR (400 MHz, CDCl , ppm) δ 9.57 (d, J = 8.0 Hz, 1H), 7.32 (d, J = 8.6 Hz, 2H), 7.28‒7.12 (m,

4H), 7.06 (d, J = 8.0 Hz, 1H), 6.98‒6.80 (m, 7H), 6.20 (dd, J = 15.1, 8.0 Hz, 1H), 2.27 (s, 3H), 2.24 (s,

3H), 2.19 (s, 3H).

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C NMR (101 MHz, CDCl , ppm) δ 193.70, 153.15, 149.80, 146.93, 144.53, 142.62, 139.32, 137.92,

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132.84, 130.64, 130.10, 129.21, 128.64, 127.98, 127.12, 125.76, 124.65, 123.53, 123.44, 122.32, 121.13,

21.45, 19.93, 19.30.

Anal. calcd. for C H NO: C, 84.98; H, 6.86; N, 3.81. Found: C, 84.94; H, 6.88; N, 3.84.

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Dye D1

Following general procedure F, a mixture of aldehyde 15 (0.47 g, 1.50 mmol), rhodanine-3-acetic acid

(0.34 g, 1.80 mmol) and AcONH (0.03 g, 0.45 mmol) was refluxed in anhydrous toluene (2 mL) for 12

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h. The crude product was purified by column chromatography using 7:18 v/v acetone/n-hexane, 2:3 v/v

acetone/n-hexane and finally 3:22 v/v methanol/toluene to collect dye D1 as a red solid. Yield: 0.31 g

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(43%), m.p. 193-195 ⁰C. UV‒vis (DMSO): λ_m_a_x(nm) 307 (ɛ = 14 679 M cm ), 469 (ɛ = 37 956 M cm

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).

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H NMR (400 MHz, DMSO-d , ppm) δ 7.65 (s, 1H), 7.47 (d, J = 9.0 Hz, 2H), 7.32–7.22 (m, 1H), 7.18

(d, J = 8.1 Hz, 1H), 7.06–6.88 (m, 5H), 6.85 (d, J = 8.9 Hz, 2H), 4.47 (s, 2H), 2.26 (s, 3H), 2.22 (s, 3H),

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2.18 (s, 3H). C NMR (101 MHz, DMSO-d , ppm) δ 193.31, 167.36, 150.71, 146.04, 143.64, 139.83,

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138.54, 134.31, 133.31, 133.06, 131.40, 130.15, 128.01, 126.81, 126.35, 124.58, 124.54, 123.53, 119.19,

118.10, 67.49, 47.74, 21.40, 19.91, 19.37.

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IR (KBr, cm ): ν = 3423 (OH); 3033 (aromatic CH); 2919, 2850 (aliphatic CH); 1711 (2×C=O); 1574

(C=C); 1506 (C-C); 1320, 1308 (C=S); 1200, 1180 (C-N).

Anal. calcd. for C H N O S : C, 66.37; H, 4.95; N, 5.73. Found: C, 66.35; H, 4.94; N, 5.74.

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Dye D2

Following general procedure F, a mixture of aldehyde 16 (0.22 g, 0.66 mmol), rhodanine-3-acetic acid

(0.15 g, 0.79 mmol) and AcONH (0.02 g, 0.19 mmol) was refluxed in glacial acetic acid (2 mL) for 2.5

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h. The crude product was purified by column chromatography using 2:23 v/v methanol/toluene as an

eluent to collect dye D2 as a red solid. Yield: 0.27 g (71%), m.p. 239-240 ⁰C. UV‒vis (DMSO): λmax (nm)

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304 (ɛ = 13 270 M cm ), 493 (ɛ = 37 190 M cm ).

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H NMR (400 MHz, DMSO-d , ppm) δ 7.57‒7.42 (m, 3H), 7.31‒7.08 (m, 3H), 6.97‒6.76 (m, 8H), 4.39

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(s, 2H), 2.23 (s, 3H), 2.20 (s, 3H), 2.16 (s, 3H).

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C NMR (101 MHz, DMSO-d , ppm) δ 192.94, 166.60, 149.96, 146.72, 145.61, 144.29, 138.27, 134.08,

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133.42, 131.23, 130.02, 129.94, 129.37, 128.67, 128.35, 127.41, 125.96, 125.78, 123.90, 122.70, 122.26,

121.29, 120.43, 48.22, 21.42, 19.91, 19.32.

IR (KBr): ν = 3412 (OH); 3033 (aromatic CH); 2918, 2850 (aliphatic CH); 1704 (2×C=O); 1600, 1565

(C=C); 1498 (C-C); 1316, 1300 (C=S); 1197, 1160 (C-N).

26 2 3 2

Anal. calcd. for C29H N O S : C, 67.68; H, 5.09; N, 5.44. Found: C, 67.65; H, 5.10; N, 5.47.

Dye D3

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Following general procedure F, a mixture of aldehyde 17 (0.25 g, 0.69 mmol), rhodanine-3-acetic acid

(0.16 g, 0.83 mmol) and AcONH (0.02 g, 0.20 mmol) was refluxed in glacial acetic acid (2.5 mL) for 45

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min. The crude product was purified by column chromatography using 2:23 v/v methanol/toluene as an

eluent to collect dye D3 as a red solid. Yield: 0.20 g (54%), m.p. 199-200 ⁰C. UV‒vis (DMSO): λ_m_a_x(nm)

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308 (ɛ = 14 740 M cm ), 503 (ɛ = 26 190 M cm ).

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H NMR (700 MHz, DMSO-d , ppm) δ 7.48–7.39 (m, 3H), 7.23–7.10 (m, 4H), 7.08–7.00 (m, 1H), 6.94–

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6.78 (m, 7H), 6.50‒6.43 (m, 1H), 4.38 (s, 2H), 2.23 (s, 3H), 2.20 (s, 3H), 2.16 (s, 3H).

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C NMR (176 MHz, DMSO-d , ppm) δ 192.55, 166.50, 149.05, 147.03, 146.92, 144.58, 139.69, 139.44,

138.19, 131.20, 129.89, 129.37, 128.98, 128.68, 127.26, 126.59, 125.79, 125.59, 125.38, 125.01, 123.74,

122.74, 122.33, 121.14, 48.20, 21.52, 21.45, 19.93, 19.30.

IR (KBr): ν = 3423 (OH); 3033 (aromatic CH); 2916, 2866 (aliphatic CH); 1703 (2×C=O); 1600, 1566,

1545 (C=C); 1503 (C-C); 1314 (C=S); 1197, 1154 (C-N).

Anal. calcd. for C H N O S : C, 68.86; H, 5.22; N, 5.18. Found: C, 68.85; H, 5.23; N, 5.15.

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3. Results and discussion

3.1 Synthesis

The new metal-free di-anchoring organic dyes based on TB scaffold TD1, TD2 and TD3 were

synthesized according to a six-step reaction as described in Scheme 1. Initially, Horner-Wittig

condensation was made to increase the polyenic chain (from n = 0 to 2). The yield of 70‒80% were

achieved by palladium-catalyzed cross-coupling reaction between protected aldehydes 3, 4 and 3,4-

dimethylaniline. The obtained corresponding diphenylamines 5, 6 and 7 were then reacted with 2,8-

dibromo-4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine [22] in the presence of

palladium(II) acetate, tri-tert-butylphosphonium tetrafluoroborate and sodium tert-butoxide to provide

intermediates based on TB scaffold 8, 9 and 10. After deprotection, the obtained penultimate dialdehydes

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11‒13 were a common synthon, which were condensed with rhodanine-3-acetic acid to give sensitizers

TD1, TD2 and TD3. These new dyes were prepared in moderate to high yields and their chemical

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structures were confirmed by H and C NMR spectroscopy. Pattern of the signals in the interval of

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3.75‒4.50 ppm in the H NMR spectrum is essential for the methylene bridge identification, proving the

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presence of the TB core. Each H NMR spectrum of TD1‒TD3 shows two doublets near each margin of

the mentioned interval and these two doublets signify that the protons in bridging methylene part (Ar-

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CH -N) are magnetically nonequivalent due to the rigid structure of the TB. As a contrasting example to

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this, signals of two protons of the other bridging methylene carbon (N-CH -N) can be observed as a

singlet at ca. 4.20 ppm in these spectrums.

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Scheme 1. Synthesis of di-anchoring dyes based on TB scaffold TD1, TD2 and TD3. Reagents and

conditions: (A) i) THF, NaH 60%, r.t.; ii) 10% aq. HCl, r.t. (B) Benzene, cat., 80 ⁰C. (C) Pd(OAc)

SPhos, H O, NaOt-Bu, dioxane, reflux. (D) Pd(OAc) , [P(t-Bu) H]BF , NaOt-Bu, toluene, reflux. (E)

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10% aq. HCl, 40 ⁰C. (F) AcONH , toluene, reflux.

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Dyes D1, D2 and D3 (Fig. 2) possessing one anchoring group were synthesized for comparison.

Firstly, compound 14 was prepared according to reported procedure [21]. Then, the diphenylamine

bearing the protected aldehyde group has been synthesized and equipped with 3-iodotoluene using the

palladium-catalyzed Buchwald-Hartwig C‒N cross-coupling reactions, to form the intermediate aldehyde

15. The Knoevenagel condensation of the obtained aldehyde with rhodanine-3-acetic acid in glacial acetic

acid gave dye D1. In parallel, Horner-Wittig condensation of aldehyde 15 with 1.1 equivalents of

tributyl(1,3-dioxalan-2-ylmethyl)phosphonium bromide gave aldehyde 16 in 78% yield. Another

vinylogation and subsequent Knoevenagel condensation produced dyes D2 and D3 (Scheme 2).

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Scheme 2. Synthesis of mono-anchoring dyes D1, D2 and D3. Reagents and conditions: (A) i) THF,

NaH 60%, r.t.; ii) 10% aq. HCl, r.t. (C) Pd(OAc) , SPhos, H O, NaOt-Bu, dioxane, reflux. (E) 10% aq.

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HCl, 40 ⁰C. (F) AcONH , toluene (or AcOH), reflux.

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3.2 Optical, electrochemical and photophysical properties

To gain an insight into the impact the number of polymethine chains and chainlength on the optical and

electrochemical properties of investigated dyes, we have performed UV-vis, FL and cyclic voltammetry

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studies of di-anchoring dyes TD1‒TD3 and their mono-anchoring analogues D1‒D3 in DMSO. As

shown in Figure 3, the absorption spectra of both, di-anchoring organic dyes based on TB scaffold TD1,

TD2, TD3 and mono-anchoring dyes D1‒D3 display two distinct absorption bands at around 270‒350 nm

and 400‒670 nm, respectively. The absorption bands in the UV region show shoulders at longer

wavelengths correspond to the π‒π* electron transitions of the conjugate system. Interestingly, the

sensitizers TD3 and its mono analogue D3 exhibit weak but clear additional absorption band at around

380 nm. This is a consequence of most extended conjugation made possible by two additional methine

units in the present series of dyes. The strong absorption bands in the visible region can be assigned to an

intramolecular charge transfer (ICT) between the triphenylamine-based donor and the electron accepting

rhodanine-3-acetic acid moiety, providing efficient charge separation at the excited state. Comparison of

the absorption spectra of π-extended dyes TD2, TD3 and D2, D3 with those of their lower homologues

TD1 and D1, clearly demonstrates that the extension of the polymethine chain results in 10‒35 nm

bathochromic shift of the absorption band compared to that of the lower homologues. Next, comparison

of the optical properties of di-anchoring dyes TD1‒TD3 with those of their mono-anchoring analogues

D1‒D3 clearly demonstrates two effects. First, the organic dyes based on TB scaffold, with the exception

of TD2, exhibit approximately twice higher extinction coefficients (Table 1) compared to those of the

references mono-anchoring dyes. The molar extinction coefficient of the charge transfer transition in

these dyes indicates a good ability for light harvesting. Second, only a negligible batochromic shift (6 nm)

was observed for the di-anchoring dye TD1 in comparison with mono-anchoring sensitizer D1. This

indicates that there is no interaction at the ground state between the two chromophores in this di-

anchoring dye. However, the comparison of the ICT absorption bands of TD2 and TD3 with references

D2 and D3 clearly indicates this interaction. Probably, this is a consequence of the extended polymethine

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chains that should ensure flexibility of these units and inspire the interaction between two chromophores

in TB-based dyes.

Figures S1-S6 show the emission and absorption spectra in the visible region of the dyes in

DMSO solution. The excitation wavelength for emission was the maximum absorption in the visible

region. It can be seen that the maximum emission wavelengths in DMSO solution follow the order D1 <

D2 < D3 and TD1 < TD2 < TD3. In addition, relatively large Stokes shifts of designing molecules were

observed between the absorption and emission spectral maxima. Moreover, the Stokes shifts were

calculated to lie within range from 193‒276 nm, meaning an enhanced geometrical difference between

the ground and excited state geometry and thus a good molecular flexibility of the excited state (Table 1).

The Stokes shifts follow the trend TD3 > TD2 > TD1 and D3 > D2 > D1. In this respect, it is easy to

postulate that the largest Stokes shifts found in TD3 and its mono-analogue D3 are due to their hexadiene

moieties between donor and acceptor that confirms a great flexibility of these dyes.

Insert Figure 3

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The absorption maxima of the investigated dyes on the TiO layer are broader and slightly blue

shifted compared to the results obtained in DMSO solutions, indicating that energy levels of the sensitizer

molecules have somewhat changed due to the interaction with TiO (Figure 4, Table 1). Upon increasing

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the number of double bonds from n = 0 to 2, progressive blue shifts are observed for each additional

methine unit, leading to the biggest shift of 30 nm for the V-shaped dye TD3 (from 526 to 496 nm) and

14 nm for its reference rod-shaped dye D3 (from 503 to 489 nm). It shows that H-aggregates form on the

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TiO surface. The absorption spectrum of mono-anchoring dye D1 (n = 0) on TiO film shows no

difference in comparison with that in DMSO solution implying that there are no evident aggregations. It

28

Article Doi

A structural study of Troger's base scaffold-based dyes for DSSC applications

DOI: 10.1016/j.dyepig.2017.04.012

Source and publish data:

Authors:

Article abstract of DOI:10.1016/j.dyepig.2017.04.012

Full text of DOI:10.1016/j.dyepig.2017.04.012

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