Synthesis and photophysical properties of novel fluorescent materials containing 2,4,6-triphenylpyridine and 1,8-naphthalimide units using Suzuki reaction

Abstract

A series of novel 2,4,6-triphenylpyridine derivatives containing 1,8-naphthalimide groups have been prepared in good yields using Suzuki couplings reactions. The relationship of the photoluminescence property of the compounds was systematically investigated via a thermogravimetric analyzer, UV-vis, fluorescence and electrochemical analyzer.

---

Introduction

Organic fluorescent compounds have been extensively investigated due to their potential applications in analytical, biological chemistry and optical sensors.^1,2 Among various strategies to improve photophysical properties, the combination of two distinctive fluorophore units which has a great contribution to increasing the fluorescence quantum yields and the shift of fluorescence emission has been an efficient way to get new high-efficiency organic fluorescent materials.³

1,8-Naphthalimide derivatives have been generally used as brilliant dyes in synthetic fibers, fluorescent optical brighteners, fluorescence switchers and liquid crystal displays.⁴ The effects of substituents on the photophysical properties of these compounds and their molecular structure are actively investigated for the qualitative and quantitative structure spectra relationships. Meanwhile, their fluorescence emission can be easily tuned (from blue to yellow, green, and even red) by the different groups at the 4-position substituted (e.g. amino or alkoxyl) or at the nitrogen atom substituted.⁵

Moreover, 2,4,6-triphenylpyridine, as a well-known electron-deficient heterocyclic unit, has been widely used as electron transporting/hole blocking materials in optoelectronic materials because these units have many excellent properties of being a better chromophore, with high electron affinity, high thermal and oxidative stability for good charge injection and transporting building blocks.⁶ In addition, introduction of the pyridinyl moiety into the polymer backbone not only increases the electron affinity of the polymer but also avoids fluorescence quenching due to the intersystem crossing (ISC) effect of the heavy atom. So far, however, there have been few reports on 2,4,6-triphenylpyridine-based conjugated optoelectronic materials with tunable band gaps.

As a consequence of our interest in exploring new high-efficiency organic fluorescent materials,⁷ in order to exploit blue emitters with reduced propensity of concentration quenching, 2,4,6-triphenylpyridine units were introduced into the 4-position of naphthalimides and the different groups were introduced at the nitrogen atom to achieve more bulky molecules (Scheme 1). As expected, these novel compounds exhibited excellent blue light emitting properties, high fluorescence quantum yields as well as high thermal stability. It is very important that these compounds be used as electron-transporting emitting material in functional materials.

Scheme 1 Synthetic routines for compound 3, 4, 7 and 8. Reagents and conditions: (a) NH₄OAc, EtOH, 80 °C; (b) cat. Pd(PPh₃)₄, Cs₂CO₃, dioxane, 80 °C; (c) acetic acid, 95 °C.

Results and discussion

Compounds 3 and 7 were synthesized according to the literature methods (Scheme 1).^4h,7 Products 4 and 8 were obtained via Pd(0) catalyzed Suzuki C–C coupling reaction (Scheme 1). The intermediate compounds 3 and 7 were characterized by MS spectrometry, ¹H NMR. The products 4 and 8 were characterized by MS spectrometry, ¹H NMR and ¹³C NMR spectroscopy.

The UV-vis absorption and fluorescence properties of the products 8a–g in CH₂Cl₂ were shown in Fig. 1 and 2. The optical properties of all compounds are summarized in Table S1.† The maximum UV-vis absorptions of compounds 8a–g are located in the range of 357–358 nm which can be ascribed to the π–π* transition of the conjugated molecular backbone of triarylpyridine. The π–π* energy gaps (E_g) of these compounds were calculated from the UV-visible absorption threshold.⁸

Fig. 1 Absorption spectra of 8a–g in CH₂Cl₂ (1.0 × 10⁻⁵ mol L⁻¹).

Fig. 2 Emission spectra of 8a–g (excited at 340 nm) in CH₂Cl₂ (5.0 × 10⁻⁶ mol L⁻¹).

Fig. 2 shows the fluorescence emission spectra of compounds 8a–g when excited at 340 nm. By altering the H, methyl and methoxycarbonyl at 4-position of the nitrogen atom substituents phenyl, 8c–e exhibited the maximum emission wavelength at 437, 435, and 441 nm in CH₂Cl₂, respectively. This is due to the introduction of electron-accepting group methoxycarbonyl to frameworks, which decrease the electron delocalization between the donor and the acceptor.^5g With the introduction of the methyl, n-butyl substituents at the nitrogen atom, compounds 8a–b show pure blue fluorescence emission with the maximum emission peaks varying from 433 to 434 nm.

The fluorescence quantum yields (Ф) were measured in the CH₂Cl₂ solution using quinine sulfate (Ф = 0.55) as control (Table S1†).⁹ In comparison with compound 8a, the fluorescence quantum yields (Ф) of compounds 8b drop greatly to 0.64, which can be ascribed to the free rotation of n-butyl groups that quenches the singlet excited states of the fluorescent molecules.^5e This difference of the quantum yields may result from the change of the molecular size.¹⁰ Compounds 8f and 8g also give blue fluorescence emission in solution. But both have much dropped fluorescence quantum yields (Ф) (<0.001) in solution which may be ascribed to the N atom linked to the naphthalene ring destructed smooth flow of the electrons in the molecule. This result might be further validated in the theoretical calculations.

The solvent effect on the fluorescence characteristics of these compounds was studied (Fig. 3 and Table 1). As shown in Fig. 3, the emission wavelength of the compound was red-shifted with the increase of solvent polarity, which indicated that they have more polar in the excited state than in the ground state¹¹ and increased polarity of the solvent will lower the energy level of the charge transfer excited state.¹² Evidences of charge transfer in the excited state observed from the solvatochromic effect in the fluorescence emission curves were investigated applying the simplified Lippert–Mataga correlation involving the absorption or the emission curves or the Stokes' shift eqn (1).¹³ The difference of absorption, [small upsilon, Greek, macron]_a, and fluorescence, [small upsilon, Greek, macron]_f, maxima is given by eqn (1).

[small upsilon, Greek, macron]_a − [small upsilon, Greek, macron]_f = mf(ε,η) + constant (1)

here, m is the slope of the graph obtained by plotting f(ε,η) versus Stokes shift ([small upsilon, Greek, macron]_a−[small upsilon, Greek, macron]_f) (Fig. 4). f(ε,η) is the orientation polarization function, defined as eqn (2). ε and η is the dielectric constant and refractive index of the solvents.

Fig. 3 Emission spectra of compound 8a in different solvents as sample.

Table 1 Solvatochromism data of compounds 8a–e

Compounds	Solvents	[small upsilon, Greek, macron]a (cm^−1)	[small upsilon, Greek, macron]f (cm^−1)	[small upsilon, Greek, macron]a−[small upsilon, Greek, macron]f (cm^−1)
8a	n-Hexane	28 329	24 752	3577
	Toluene	28 169	23 310	4859
	CH2Cl2	27 933	23 095	4838
	DMF	27 933	22 472	5461
8b	n-Hexane	28 011	24 691	3320
	Toluene	28 011	23 148	4863
	CH2Cl2	27 933	23 041	4892
	DMF	27 933	22 472	5461
8c	n-Hexane	28 409	24 691	3718
	Toluene	28 169	22 989	5180
	CH2Cl2	28 090	22 883	5207
	DMF	28 090	22 321	5769
8d	n-Hexane	27 933	24 876	3057
	Toluene	27 855	23 095	4760
	CH2Cl2	28 011	22 989	5022
	DMF	28 011	22 422	5589
8e	n-Hexane	27 933	25 641	2292
	Toluene	27 778	23 696	4082
	CH2Cl2	28 011	22 676	5335
	DMF	28 011	22 472	5539

---

Fig. 4 Plot of Stokes shift (Δν) with Lippert's polarity parameter f(ε,η) for compound 8a.

The glass transition temperatures (T_g) and decomposition temperatures (T_d) were determined by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), respectively, using a heating rate of 10 °C min⁻¹. After the first DSC analytical scan, the sample was cooled to room temperature,the isotropic liquid changed into a glassy state. Subsequently the glassy sample was reheated for the second run and the glass transition temperatures of these compounds were observed at 50–97 °C (Table 2).¹⁴ The experiment results revealed that the thermal stability of these compounds seemed to be encouraging. Thermal decomposition temperatures for 8 were observed over 360 °C.

Table 2 Thermal and electrochemical properties of the compounds 8

Compounds	Band gap^a	EHOMO/ELUMO^a (eV)	Eg^b (eV)	E^oxonset^c (V)	EHOMO/ELUMO^d (eV)	Td/Tg^e (°C)
a DFT/B3LYP calculated values.b Optical energy gaps calculated from the edge of the electronic absorption band.c Oxidation potential in CH2Cl2 (10^−3 mol L^−1) containing 0.1 mol L^−1 (n-C4H9)4NPF6 with a scan rate of 100 mV s^−1.d EHOMO was calculated by Eox + 4.4 V, and ELUMO = EHOMO−Eg.e Measured by TG-DTA analysis under N2 at a heating rate of 10 °C min^−1.
8a	3.54	−6.18/−2.64	3.54	0.75	−5.15/−1.61	360/72
8b	3.56	−6.18/−2.62	3.63	0.82	−5.22/−1.59	—
8c	3.57	−6.18/−2.61	3.66	0.84	−5.24/−1.58	410/73
8d	3.59	−6.17/−2.58	3.65	0.83	−5.23/−1.58	420/73
8e	3.47	−6.20/−2.73	3.55	0.77	−5.17/−1.62	429/52
8f	3.26	−5.87/−2.61	3.57	0.73	−5.13/−1.56	440/50
8g	3.22	−5.84/−2.62	3.79	0.96	−5.36/−1.57	410/97

---

The electrochemical properties of compounds 8a–g are explored by the cyclic voltammetry (CV) in CH₂Cl₂ in the presence of tetrabutylammonium hexafluorophosphate (0.10 mol L⁻¹) as the supporting electrolyte (Table 2). All of compounds have one reversible oxidation peak which indicated the presence of a stable cation radical (Fig. 5). The energy of the HOMO of them was calculated with reference to ferrocene (4.8 eV) and ranges from −5.13 to −5.36 eV.^15,16 The HOMO energy level is close to the most widely used hole-transport material 1,4-bis(1-naphthylphenylamino)biphenyl (NBP) (−5.20 eV, −2.4 eV), which might be beneficial for the hole-transport capacity.¹⁵ Similarly, the optical edge was utilized to deduce the band gap and the lowest unoccupied molecular orbital (LUMO) energies. These compounds have high LUMO levels (−1.56 to −1.62 eV), which represent a small barrier for the electron injection from a commonly used cathode such as barium.¹⁷

Fig. 5 Cyclic voltammogram of compounds 8b, 8c (1 × 10⁻³ mol L⁻¹) as sample, in 0.1 mol L⁻¹ Bu₄NPF₆–CHCl₃, scan rate 100 mV s⁻¹.

The electronic configurations were further examined using the theoretical models implanted in the Gaussian 09 program.¹⁸ The calculations based upon density functional theory (DFT) (B3LYP; 6-31G*) were carried out to obtain information about the HOMO and LUMO distributions of the compounds 8a–g in the ground state. All of these compounds in Table 2 possess a high HOMO energy level (−5.84 to −6.20 eV), which could lead to their better hole-transport properties (Fig. 6).¹⁶ It can be found in Fig. 6 that the HOMO orbital of 8a was distributed in the triarylpyridine core, and the LUMO was distributed in the 1,8-naphthalimide backbone. However, in compounds 8f and 8g, the HOMO orbital was distributed in the naphthalene ring. This may be the explanation of why compounds 8f and 8g have lower fluorescence quantum yields and HOMO energy. The low LUMO energy of these compounds (−2.58 to −2.73 eV) is supposed to facilitate the acceptance of electrons from the cathode. It is generally indicative of a HOMO/LUMO absorption transition to bear a significant charge-transfer character. The higher HOMO/LUMO energy levels than those corresponding estimations from the experimental data may be related to various effects from conformation and solvents, which have not been taken into account here. The vertical excitation energies and oscillator strengths were obtained for the lowest singlet transitions at the optimized ground state equilibrium geometries by using TDDFT at the same hybrid functional and the basis set.¹³ The UV-vis absorption spectra and fluorescence spectra of the compounds 8a–e by theoretical studies using the TDDFT method ((B3LYP; 6-31G*)) were shown in Fig. S2 and 3.†

Fig. 6 Calculated molecular orbitals and energy levels of fluorophores 8a–g.

Conclusions

In summary, a series of novel fluorescence compounds containing 2,4,6-triphenylpyridine and 1,8-naphthalimide units have been prepared by a stepwise route in good yields. The optical properties clearly indicate that the fluorescent emission properties of these compounds rely largely on the position of substituents and the solvent effect. All compounds exhibit high fluorescence quantum yields (except 8f and 8g), high thermal stability, excellent fluorescence emission of blue. The CV and calculated data further demonstrate that although the calculated energy levels are lower than those determined by experiments, the trends of compounds 8a–e in the band gaps are in good agreement with the ones obtained by UV-vis and CV measurements of these compounds. The photophysical and electrochemical properties indicate that the compounds might have potential applications as functional materials.

Experimental section

General

All solvents were carefully dried and freshly distilled according to common laboratory techniques. All reactants were commercially available and used without further purification. All reactions were monitored using thin layer chromatography (TLC) on pre-coated silica gel 60 F₂₅₄ (mesh); spots were observed under UV light. Melting points were recorded on electrothermal digital melting point apparatus and were uncorrected. Nuclear Magnetic Resonance (NMR) spectra was recorded at 295 K on a Bruker Avance DPX-400 MHz spectrometer using CDCl₃ as solvent and TMS as internal standard. UV-vis spectra were recorded on a Shimadzu UV-2501PC spectrometer. Fluorescence spectra were obtained on a Hitachi FL-4500 spectrofluorometer. High resolution mass spectroscopy (HRMS) data were measured using micro TOF-Q(APCI) instrument. Cyclic voltammetry measurements were carried out under an inert nitrogen atmosphere with an Autolab potentiostat PGSTAT 10 using a three-electrode cell (platinum was used as the working electrode and as a counter electrode, and scanning calomel electrode as a reference electrode). The rate scan was 100 mV s⁻¹ and the supporting electrolyte was a Bu₄NPF₆ (0.1 mol L⁻¹) solution in CH₂Cl₂. TGA and DSC measurements were carried out on SDT 2960 and DSC 2010 instruments. The thermal analyses were carried out under a nitrogen flow and with a heating rate of 10 °C min⁻¹.

The procedure for the synthesis of compounds 3

Compound 3 were synthesized according to literature method.⁷ A solution of 4-bromobenzaldehyde (10.0 mmol), phenyl methyl ketone (20.0 mmol), ammonium acetate (100 mmol) in ethanol (150 mL) was refluxed at 80 °C for 24 h. After the finish, filtered the mixture and recrystallized the precipitate with ethanol to give the pure compound 3.

4-(4-Bromophenyl)-2,6-diphenylpyridine (3). Yield 30%, white powder, ¹H NMR (400 MHz, CDCl₃) δ 8.19 (d, J = 7.1 Hz, 4H), 7.84 (s, 2H), 7.64 (q, J = 8.6 Hz, 4H), 7.52 (t, J = 7.4 Hz, 4H), 7.46 (t, J = 6.7 Hz, 2H).

The procedure for the preparation of compound 4

Compound 3 (5 mmol), bis(pinacolato)diboron (5 mmol), cesiumcarbonate (7.5 mmol), Pd(PPh₃)₄ (0.2 mmol) and dioxane (25 mL) were added into a 50 mL branch-pipe round bottom flask. The mixture was degassed by gently bubbling nitrogen for 30 min and then heated in an oil bath at 85 °C until completion (72 h). After cooling, the product was extracted with CH₂Cl₂, washed with water, dried over Na₂SO₄, filtered, concentrated and further purified by column chromatography (silica gel, hexane/ethyl acetate, 50/1, v/v) to afford compound 4.

2,6-Diphenyl-4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (4). Yield 75%, white powder, Mp: 165–168 °C, ¹H NMR (400 MHz, CDCl₃) δ 8.20 (d, J = 7.6 Hz, 4H), 7.98 (d, J = 7.6 Hz, 2H), 7.92 (s, 2H), 7.77 (d, J = 7.6 Hz, 2H), 7.53 (t, J = 7.4 Hz, 4H), 7.46 (t, J = 7.1 Hz, 2H), 1.39 (s, 12H). ¹³C NMR (100 MHz, CDCl₃) δ 157.4, 135.6, 129.3, 128.7, 127.4, 126.5, 117.6, 84.0, 24.9. HRMS (APCI) m/z:calcd for C₂₉H₂₉BNO₂, (M + H)⁺: 434.2291, found: 434.2351.

General procedure for the synthesis of compounds 7

Compounds 7 were synthesized according to literature method.^4h A solution of 4-bromo-1,8-naphthalic anhydride 5 (5 mmol), alkyl amine 6 (or aromatic amine) (6 mmol) in acetic acid (30 mL) was refluxed at 95 °C for 24 h. After the finish, filtered the mixture and recrystallized the precipitate with ethanol (or acetic acid) to give the pure compounds 7.

6-Bromo-2-methyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (7a). Yield 70%, yellow powder, ¹H NMR (400 MHz, CDCl₃): δ 8.67 (d, J = 7.2 Hz, 1H), 8.57 (d, J = 8.5 Hz, 1H), 8.42 (d, J = 7.8 Hz, 1H), 8.05 (d, J = 7.7 Hz, 1H), 7.85 (t, J = 7.9 Hz, 1H), 3.56 (s, 3H).

6-Bromo-2-butyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (7b). Yield 72%, yellow powder, ¹H NMR (400 MHz, CDCl₃): δ 8.66 (d, J = 7.2 Hz, 1H), 8.57 (d, J = 8.4 Hz, 1H), 8.42 (d, J = 7.7 Hz, 1H), 8.04 (d, J = 7.9 Hz, 1H), 7.85 (t, J = 7.8 Hz, 1H), 4.18 (t, J = 7.4 Hz, 2H), 1.74–1.65 (m, 2H), 1.45 (dd, J = 14.8, 7.4 Hz, 2H), 0.98 (t, J = 7.3 Hz, 3H).

6-Bromo-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (7c). Yield 69%, yellow powder, ¹H NMR (400 MHz, CDCl₃): δ 8.71 (d, J = 7.3 Hz, 1H), 8.64 (d, J = 8.5 Hz, 1H), 8.47 (d, J = 7.9 Hz, 1H), 8.09 (d, J = 7.8 Hz, 1H), 7.90 (t, J = 7.9 Hz, 1H), 7.57 (t, J = 7.5 Hz, 2H), 7.50 (t, J = 7.4 Hz, 1H), 7.32 (d, J = 7.8 Hz, 2H).

6-Bromo-2-p-tolyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (7d). Yield 70%, yellow powder, ¹H NMR (400 MHz, CDCl₃): δ 8.71 (d, J = 7.3 Hz, 1H), 8.63 (d, J = 8.5 Hz, 1H), 8.46 (d, J = 7.7 Hz, 1H), 8.08 (d, J = 7.7 Hz, 1H), 7.89 (t, J = 7.8 Hz, 1H), 7.36 (t, J = 7.6 Hz, 2H), 7.20 (d, J = 7.4 Hz, 2H), 2.45 (s, 3H).

6-Bromo-2-(naphthalen-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (7e). Yield 65%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.74 (d, J = 7.3 Hz, 1H), 8.69 (d, J = 8.5 Hz, 1H), 8.49 (d, J = 7.8 Hz, 1H), 8.12 (d, J = 7.8 Hz, 1H), 8.01 (d, J = 8.3 Hz, 1H), 7.98–7.89 (m, 2H), 7.63 (m, 2H), 7.51 (t, J = 8.6 Hz, 2H), 7.47–7.40 (m, 1H).

6-Bromo-2-(naphthalen-2-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (7f). Yield 65%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.73 (d, J = 8.2 Hz, 1H), 8.66 (d, J = 8.5 Hz, 1H), 8.49 (d, J = 7.9 Hz, 1H), 8.10 (d, J = 7.9 Hz, 1H), 8.02 (d, J = 8.6 Hz, 1H), 7.95–7.84 (m, 4H), 7.54 (m, 2H), 7.39 (m, 1H).

Methyl 4-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzoate (7g). Yield 65%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.71 (d, J = 7.3 Hz, 1H), 8.66 (d, J = 8.5 Hz, 1H), 8.46 (d, J = 7.9 Hz, 1H), 8.23 (d, J = 8.4 Hz, 2H), 8.10 (d, J = 7.9 Hz, 1H), 7.91 (t, J = 7.9 Hz, 1H), 7.41 (d, J = 8.4 Hz, 2H), 3.97 (s, 3H).

General procedure for the synthesis of compounds 8

Compounds 7a–g (1 mmol), 4 (1.2 mmol), cesiumcarbonate (1.5 mmol), Pd(PPh₃)₄ catalyst (0.04 mmol) and dioxane (5 mL) were added into a 50 mL branch-pipe round bottom flask. The mixture was degassed by gently bubbling nitrogen for 30 min and then heated in an oil bath at 85 °C until completion (72 h). After cooling, the product was extracted with CH₂Cl₂, washed with water, dried over Na₂SO₄, filtered, concentrated and further purified by recrystallizing from dichloromethane and ethanol to obtain compounds 8a–g. The seven starburst compounds synthesized are easily soluble in common organic solvents such as chloroform, toluene, ethyl acetate and DMF.

6-(4-(2,6-Diphenylpyridin-4-yl)phenyl)-2-methyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (8a). Yield 65%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.69 (t, J = 8.3 Hz, 2H), 8.34 (d, J = 8.5 Hz, 1H), 8.25 (d, J = 7.7 Hz, 4H), 8.00 (s, 2H), 7.96 (d, J = 7.8 Hz, 2H), 7.76 (m, 2H), 7.70 (d, J = 7.8 Hz, 2H), 7.56 (t, J = 7.5 Hz, 4H), 7.49 (t, J = 7.1 Hz, 2H), 3.62 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 164.5, 164.3, 157.7, 149.4, 146.0, 139.5, 139.2, 132.5, 131.3, 130.8, 130.0, 129.3, 128.7, 127.9, 127.5, 127.1, 122.8, 121.9, 117.1, 27.1. HRMS (APCI) m/z: calcd for C₃₆H₂₅N₂O₂ [M + H]⁺: 517.1916, found: 517.1916.

2-Butyl-6-(4-(2,6-diphenylpyridin-4-yl)phenyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (8b). Yield 63%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.69 (t, J = 8.1 Hz, 2H), 8.33 (d, J = 8.3 Hz, 1H), 8.24 (d, J = 7.4 Hz, 4H), 8.04–7.94 (m, 4H), 7.80–7.70 (m, 4H), 7.60–7.50 (m, 6H), 4.26–4.20 (m, 2H), 1.76 (t, J = 6.5 Hz, 2H), 1.51–1.46 (m, 2H), 1.00 (t, J = 7.3 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 164.1, 157.4, 139.9, 132.3, 131.3, 130.8, 129.9, 129.6, 128.8, 127.9, 127.5, 127.1, 123.0, 117.70, 40.3, 30.2, 20.4, 13.8. HRMS (APCI) m/z: calcd for C₃₉H₃₁N₂O₂ [M + H]⁺: 559.2386, found: 559.2350.

6-(4-(2,6-Diphenylpyridin-4-yl)phenyl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (8c). Yield 60%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.74 (t, J = 8.0 Hz, 2H), 8.39 (d, J = 7.8 Hz, 1H), 8.24 (d, J = 7.5 Hz, 4H), 8.05–7.97 (m, 4H), 7.84–7.73 (m, 4H), 7.57 (m, 9H), 7.37 (d, J = 7.6 Hz, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 164.4, 164.2, 157.6, 146.3, 139.5, 139.1, 135.3, 132.7, 131.7, 131.2, 130.7, 130.1, 129.4, 129.1, 128.7, 128.0, 127.6, 127.2, 123.1, 122.2, 117.2. HRMS (APCI) m/z: calcd for C₄₁H₂₇N₂O₂ [M + H]⁺: 579.2073, found: 579.2071.

6-(4-(2,6-Diphenylpyridin-4-yl)phenyl)-2-ptolyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (8d). Yield 60%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.72 (t, J = 8.2 Hz, 2H), 8.38 (d, J = 9.1 Hz, 1H), 8.25 (d, J = 6.8 Hz, 4H), 8.07–7.94 (m, 4H), 7.83–7.71 (m, 4H), 7.53 (m, 6H), 7.38 (d, J = 7.2 Hz, 2H), 7.23 (s, 2H), 2.46 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 164.5, 164.3, 157.4, 146.1, 138.7, 132.6, 131.7, 131.2, 130.8, 130.1, 129.7, 129.4, 128.8, 128.2, 128.2, 127.5, 127.1, 123.2, 117.7, 21.3. HRMS (APCI) m/z: calcd for C₄₂H₂₉N₂O₂ [M + H]⁺: 593.2229, found: 593.2214.

6-(4-(2,6-Diphenylpyridin-4-yl)phenyl)-2-(naphthalen-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (8e). Yield 60%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.76 (t, J = 8.3 Hz, 2H), 8.43 (d, J = 7.7 Hz, 1H), 8.24 (d, J = 6.7 Hz, 4H), 8.09–7.96 (m, 6H), 7.82 (m, 4H), 7.68 (d, J = 7.5 Hz, 2H), 7.56 (m, 8H), 7.46 (t, J = 7.0 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃) δ 164.4, 157.5, 146.4, 139.7, 138.8, 134.5, 132.9, 132.2, 131.9, 131.4, 130.8, 130.2, 129.4, 128.8, 128.0, 127.7, 127.6, 127.1, 126.7, 125.6, 122.2, 121.8, 117.5. HRMS (APCI) m/z: calcd for C₄₅H₂₉N₂O₂ [M + H]⁺: 629.2229, found: 629.2220.

6-(4-(2,6-Diphenylpyridin-4-yl)phenyl)-2-(naphthalen-2-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (8f). Yield 65%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.78 (t, J = 8.1 Hz, 2H), 8.44 (d, J = 8.3 Hz, 1H), 8.28 (d, J = 7.3 Hz, 4H), 8.08–7.90 (m, 8H), 7.84 (m, 2H), 7.76 (d, J = 7.9 Hz, 2H), 7.61–7.45 (m, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 164.5, 164.3, 157.7, 149.3, 146.4, 139.4, 133.6, 133.2, 132.8, 131.7, 131.2, 130.7, 130.2, 129.2, 128.7, 128.2, 127.8, 127.2, 126.7, 126.4, 126.1, 123.2, 122.1, 117.0. HRMS (APCI) m/z: calcd for C₄₅H₂₉N₂O₂ [M + H]⁺: 629.2229, found: 629.2220.

Methyl-4-(6-(4-(2,6-diphenylpyridin-4-yl)phenyl)-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzoate (8g). Yield 65%, yellow powder, ¹H NMR (400 MHz, CDCl₃) δ 8.73 (t, J = 8.1 Hz, 2H), 8.42 (d, J = 8.5 Hz, 1H), 8.26 (d, J = 7.9 Hz, 5H), 8.02–7.94 (m, 4H), 7.81 (m, 2H), 7.69 (m, 3H), 7.55 (t, J = 7.3 Hz, 4H), 7.47 (m, 4H), 3.97 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 164.1, 157.7, 139.5, 139.2, 133.0, 131.8, 131.3, 130.7, 129.5, 128.7, 128.0, 127.6, 127.2, 117.1, 52.3. HRMS (APCI) m/z: calcd for C₄₃H₂₉N₂O₄ [M + H]⁺: 637.2127 found: 637.2290.

Acknowledgements

We are grateful to Dr Guo-Lan Dou in China University of Mining and Technology for great computational assistances and we are grateful for financial support from the Key Basic Research Project of the Natural Science Foundation of the Jiangsu Higher Education Institutions, China (No. 13KJA430002, 14KJA430003).

Notes and references

1. (a) S. Miyata and H. S. Nalwa, Organic Electroluminescent Materials and Derivatives, Gordon and Breach, Tokyo, 1997, p. 1; (b) T. J. J. Muller, Functional Organic Materials, Wiley-VCH, Weinheim, Germany, 2007, p. 1; (c) C. W. Tang and S. A. Van Slyke, Appl. Phys. Lett., 1987, 51, 913; (d) A. J. Berresheim, M. Muller and K. Mullen, Chem. Rev., 1999, 98, 1747.
2. (a) L. Pu, Chem. Rev., 1998, 98, 2405; (b) B. S. Gaylord, S. Wang, A. J. Heeger and G. C. Bazan, J. Am. Chem. Soc., 2001, 123, 6417; (c) H. Shimizu, K. Fujimoto, M. Furusyo, H. Maeda, Y. Nanai, K. Mizuno and M. Inouye, J. Org. Chem., 2007, 72, 1530; (d) P. Panda, D. Veldman, J. Sweelssen, J. J. A. M. Bastiaansen, B. M. W. Langeveld-Voss and S. C. J. Meskers, J. Phys. Chem. B, 2007, 111, 5076; (e) S. A. Jenekhe, Adv. Mater., 1995, 7, 309; (f) A. Kraft, A. C. Grimsdale and A. B. Holmes, Angew. Chem., Int. Ed., 1998, 37, 402.
3. (a) F. Hide, M. A. Diaz-Garcia, B. J. Schartz and A. J. Heeger, Acc. Chem. Res., 1997, 30, 430; (b) M. K. Ng, D. C. Lee and L. Yu, J. Am. Chem. Soc., 2002, 124, 11862; (c) T. L. Benanti, P. Saejueng and D. Venkataraman, Chem. Commun., 2007, 692.
4. (a) H. Tian, T. Xu, Y. B. Zhao and K. C. Chen, J. Chem. Soc., Perkin Trans. 2, 1999, 545; (b) K. Hasharoni, H. Levanon, S. R. Greenfield, D. J. Gosztola, W. A. Svec and M. R. Wasielewski, J. Am. Chem. Soc., 1996, 118, 10228; (c) X. Poteau, A. I. Brown, R. G. Brown, C. Holmes and D. Matthew, Dyes Pigm., 2000, 47, 91; (d) I. Grabchev, I. Moneva, V. Bojinov and S. Guittonneau, J. Mater. Chem., 2000, 10, 1291; (e) A. T. Peters and M. J. Bide, Dyes Pigm., 1985, 6, 349; (f) J. X. Yang, X. L. Wang, S. Tu and L. H. Xu, Dyes Pigm., 2005, 67, 27; (g) J. Li, F. Meng, H. Tian, J. Mi and W. Ji, Chem. Lett., 2005, 34, 922; (h) B. Bian, S. J. Ji and H. B. Shi, Dyes Pigm., 2008, 76, 348; (i) H. Tian, J. Gan, K. Chen, J. He, Q. L. Song and X. Y. Hou, J. Mater. Chem., 2002, 12, 1262.
5. (a) D. Kolosov, V. Adamovich, P. Djurovich, M. E. Thompson and C. Adachi, J. Am. Chem. Soc., 2002, 124, 9945; (b) S. Saha and A. Samanta, J. Phys. Chem. A, 2002, 106, 4763; (c) S. Takahashi, K. Nozaki, M. Kozaki, S. Suzuki, K. Keyaki, A. Ichimura, T. Matsushita and K. Okada, J. Phys. Chem. A, 2008, 112, 2533; (d) M. S. Alexiou, V. Tychopoulos, S. Ghorbanian and J. H. P. Tyman, J. Chem. Soc., Perkin Trans. 2, 1990, 837; (e) D. Yuan, R. G. Brown, J. D. Hepworth, M. S. Alexiou and J. H. P. Tyman, J. Heterocycl. Chem., 2008, 45, 397; (f) O. V. Prezhdo, B. V. Uspenskii, V. V. Prezhdo, W. Boszczyk and V. B. Distanov, Dyes Pigm., 2007, 72, 42; (g) H. Ulla, B. Garudachari, M. N. Satyanarayan, G. Umesh and A. M. Isloor, Opt. Mater., 2014, 36, 704.
6. (a) N. Li, P. Wang, S. L. Lai, W. Liu, C. S. Lee, S. T. Lee and Z. Liu, Adv. Mater., 2010, 22, 527; (b) J. X. Yang, X. T. Tao, C. X. Yuan, Y. X. Yan, L. Wang, Z. Liu, Y. Ran and M. H. Jiang, J. Am. Chem. Soc., 2005, 127, 3278; (c) N. Li, S. L. Lai, W. Liu, P. Wang, J. You, C. S. Lee and Z. Liu, J. Mater. Chem., 2011, 21, 12977; (d) H. Akdas-Kilig, J. P. Malval, F. Morlet-Savary, A. Singh, L. Toupet, I. Ledoux-Rak, J. Zyss and H. L. Bozec, Dyes Pigm., 2011, 92, 681; (e) D. Jana and B. K. Ghorai, Tetrahedron Lett., 2012, 53, 1798; (f) Q. Ran, J. Ma, T. Wang, S. Fan, Y. Yong, S. Qi, Y. Cheng and F. Song, New J. Chem., 2016, 40, 6281.
7. H. Y. Wang, L. F. Chen, X. L. Zhu, C. Wang, Y. Wan and H. Wu, Spectrochim. Acta, Part A, 2014, 121, 355.
8. N. X. Hu, S. Xie, Z. D. Popovic, B. A. Wong and M. Hor, Synth. Met., 2000, 111, 421.
9. P. Wei, X. Bi, Z. Wu and Z. Xu, Org. Lett., 2005, 15, 3199.
10. Z. Zhao, X. Xu, Z. Jiang, P. Lu, G. Yu and Y. Liu, J. Org. Chem., 2007, 72, 8345.
11. (a) N. Sarkar, K. Das, D. N. Nath and K. Bhattacharyya, Langmuir, 1994, 10, 326; (b) C. Reichardt, Angew. Chem., Int. Ed., 1979, 18, 98.
12. X. M. Wang, D. Wang, G. Y. Zhou, W. T. Yu, Y. F. Zhou, Q. Fang and M. H. Jiang, J. Mater. Chem., 2001, 11, 1600.
13. O. Treutler and R. Ahlrichs, J. Chem. Phys., 1995, 102, 346.
14. S. L. Tao, L. Li, J. S. Yu, Y. D. Jiang, Y. C. Zhou, C. S. Lee, S. T. Lee, X. H. Zhang and O. Kwon, Chem. Mater., 2009, 21, 1284.
15. S. Janietz, D. D. C. Bradley, M. Grell, C. Giebeler, M. Inbaselatan and E. P. Woo, Appl. Phys. Lett., 1998, 73, 2453.
16. J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bässler, M. Porsch and J. Daub, Adv. Mater., 1995, 7, 551.
17. M. Thelakkat and H. W. Schmidt, Adv. Mater., 1998, 10, 219.
18. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria and M. A. Robb, Gaussian 09, Gaussian Inc., Wallingford CT, USA, 2009.

---

Footnote

† Electronic supplementary information (ESI) available: Experimental procedures, spectral data for all new compounds. See DOI: 10.1039/c6ra16408k

---