Coumarin–tetraphenylethylene regioisomers: synthesis, photophysical and aggregation-induced emission properties

T. Sheshashena Reddy , Hyungkyu Moon and Myung-Seok Choi *
Division of Chemical Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul, South Korea. E-mail: mchoi@konkuk.ac.kr

Received 3rd January 2020 , Accepted 8th February 2020

First published on 10th February 2020


Coumarin–tetraphenylethylene (CTPE) regioisomers with different linkage types (single-bond, vinyl, and acetylene) and substitution positions (coumarin C5, C6, C7) were synthesized and characterized using 1H NMR, 13C NMR, and high-resolution mass spectroscopy. The effects of substitution position and conjugation in CTPEs 1–9 on absorption, fluorescence, and aggregation-induced emission enhancement were explored. Electronic absorption and emission spectra indicate that CTPEs with C7 substitution are red-shifted compared to those substituted at C5 or C6. CTPEs 1–9 form aggregates in tetrahydrofuran/water (1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v) and exhibit aggregation-induced emission. Nanoaggregates were characterized using scanning electron microscopy and dynamic light scattering. The structure of CTPE 1 was confirmed by single crystal X-ray diffraction analysis.


Introduction

Over the last two decades, extensive efforts have been made to develop new solid-state emissive organic materials for potential applications in biology and material science.1 In 2001, Tang et al. discovered aggregation-induced emission (AIE); since then, the study of AIE has garnered great interest for applications in a variety of fields, including biosensors, biological imaging, environmental monitoring, optoelectronics, green energy devices, chemosensors, and theranostics.2–9 The AIE phenomenon arises due to restriction of molecular motions.

Coumarins are dyes that can be found in a variety of plant sources.10 Coumarin was first isolated from Tonka beans by August Vogel in 1820;11 William H. Perkin was the first to chemically synthesize coumarin.12 Coumarin is desirable for application in various fields such as laser dyes,13 dye-sensitized solar cells,14 organic light-emitting diodes,15 nonlinear optical materials,16 anticancer treatment,17 anti-inflammatory activities,18 antidepressant activities,19 biosensors,20 and fluorescent sensors.21,22 Simple coumarin (2-oxo-2H-chromene) is not fluorescent; the optical properties of substituted coumarins depend significantly on the type and position of the substituent on the coumarin ring.23 Coumarin derivatives substituted with an electron-donating group at the 7-position are highly fluorescent compared to those substituted at the 6- and 5-positions.24

Recently, coumarin-based AIE fluorophores have been reported. Shreykar et al. reported the synthesis and AIE properties of a coumarin–thiazole hybrid dye (Cou-thiazole; Chart 1).25 They observed a twofold increase in emission enhancement upon aggregation of the thiazole hybrid dye in 60% DMF/H2O. Yan et al. synthesized triphenylamine–coumarin dyads and investigated their AIE properties. Triphenylamine–coumarin dyads display AIE at 95% H2O (Cou-tpa; Chart 1).26 Chen et al. developed a Hg2+ ion sensor based on the AIE of pyrazolo[3,4-b]pyridine-based coumarin (Cou-pyrazole; Chart 1).27 Qi et al. synthesized a coumarin Schiff-base and used it as an AIE-based cysteine sensor.28 We recently reported thioether-linked naphthalimide–coumarins and aromatic thioethers–naphthalimides AIE molecules.29,30 Further, we also reported the position and conjugation-dependent aggregation-induced emission enhancement (AIEE) properties of naphthalimide–TPEs.31


image file: d0nj00037j-c1.tif
Chart 1 Structures of previously reported coumarin-based AIEE molecules.

We attached a TPE group via different linkages (single-bond, vinyl, and acetylene) to various positions on coumarin. Subsequently, we investigated the effect of position and conjugation on absorption and AIE. Herein, we describe the synthesis of these CTPE regioisomers and investigate the effect of conjugation and position on their properties of absorption, fluorescence, and AIE.

Results and discussion

Synthesis of CTPEs

The synthesis of CTPEs 1–9 and their structures are shown in Scheme 1 and Chart 2, respectively. Bromocoumarins (10–12),32,33 4,4,5,5-tetramethyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1,3,2-dioxaborolane,34 (2-(4-vinylphenyl)ethane-1,1,2-triyl)tribenzene,35 and (2-(4-ethynylphenyl)ethane-1,1,2-triyl)tribenzene36 were synthesized according to the previously reported procedures.
image file: d0nj00037j-s1.tif
Scheme 1 Synthesis of CTPEs 1–9.

image file: d0nj00037j-c2.tif
Chart 2 Structures of CTPEs 1–9.

CTPEs 1–3 were synthesized using the Suzuki–Miyaura cross-coupling reaction of 4,4,5,5-tetramethyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1,3,2-dioxaborolane with 10 or 11 or 12. Pd(PPh3)4 and sodium carbonate were respectively employed as the catalyst and the base in THF at 70 °C overnight. The yields of CTPEs 1, 2, and 3 were 64, 60, and 57%, respectively.31 CTPEs 4–6 were synthesized using the Heck coupling reaction of (2-(4-vinylphenyl)ethane-1,1,2-triyl)tribenzene with 10 or 11 or 12via a Pd(OAc)2/P(o-tolyl)3 catalyst system in a mixture of DMF and triethylamine at 90 °C for 24 h. The yields of CTPEs 4, 5, and 6 were 66, 68, and 69%, respectively.37 CTPEs 7–9 were synthesized using the Sonogashira cross-coupling reaction of (2-(4-ethynylphenyl)ethane-1,1,2-triyl)tribenzene with 10 or 11 or 12via a Pd(PPh3)2Cl2/CuI catalyst system and triethylamine as the base in THF at 60 °C for 12 h. The yields of CPTEs 7, 8, and 9 were 71, 68, and 74%, respectively.31 CTPEs 1–9 were characterized using 1H NMR, 13C NMR, and HRMS techniques (ESI, Fig. S1–S18).

X-ray analysis

A colorless single crystal of 1 was obtained by slow diffusion of ethanol into dichloromethane solution at room temperature. The CTPE 1 crystallized in the monoclinic P21/c space group. The crystal structure of CTPE 1 is shown in Fig. 1. The single crystal structure of CTPE 1 shows coumarin unit in one plane and TPE phenyl rings in twisted geometry. The twisted phenyl rings in TPE unit, reduces the π–π staking interaction in solid state and enhances emission intensity in aggregated state. The crystal structure data refinement parameters are given in Table S1 (ESI). Various types of intermolecular interactions observed in CTPE 1. TPE unit carbons C18, C18 and C22 forms C–H⋯π interaction with H20, H10 and H11 hydrogen atoms with 2.849 Å, 2.879 Å and 2.864 Å bond lengths respectively. Coumarin unit carbons C27, C28 and C31 forms C–H⋯π interactions with H16, H16 and H23 hydrogen atoms with 2.735 Å, 2.891 Å and 2.883 Å bond lengths respectively. Coumarin unit carbons C27 and C28 forms C–H⋯π interactions with H16 hydrogen atoms forms 1-D ladder. Coumarin unit O2 oxygen atom forms intermolecular interactions with H23, H12 and H30 hydrogen atoms with 2.67 Å, 2.609 Å and 2.636 Å bond lengths respectively. These supramolecular intermolecular interactions in CTPE 1, leads to the formation of 2-D network (Fig. 1).
image file: d0nj00037j-f1.tif
Fig. 1 (a) Crystal structure of CTPE 1. (b) Intermolecular interactions (C–H⋯π interactions between C27–H16 and C28–H16) in crystal packing diagram of CTPE 1 forming 1-D ladder. (c) Various intermolecular interactions in crystal packing diagram of CTPE 1 forming 2-D framework.

Photophysical properties

Electronic absorption and emission spectra of CTPEs and their precursors were recorded in THF and THF/H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v) at room temperature. Normalized absorption and emission spectra of the CTPEs are shown in Fig. 2 and Fig. S19 (ESI); the corresponding data are listed in Table 1. Bromocoumarins 10, 11, and 12 exhibit longer absorption maxima at 322, 315, and 284 nm, respectively; this is attributed to a π–π* electronic transition. CTPEs 1–9 have longer absorption maxima at 312, 325, 348, 350, 346, 376, 338, 333, and 354 nm, respectively. The absorption of the 7-substituted CTPEs was shifted bathochromically by 36, 23, 26, 30, 16 and 11 nm in comparison with the corresponding 5 and 6-substituted CTPEs analogues with single-bond, vinyl and acetylene linkages respectively. CTPEs connected at position C7 of coumarin display red-shifted absorption (bathochromic shift) compared to those modified at the C6 and C5 positions; this may result from intramolecular charge transfer.38 Among the CTPEs, the greatest bathochromic shift was observed for C7-substituted CTPE 6. Absorption maxima for the CTPEs follow the order 6 > 9 > 4 > 3 > 5 > 7 > 8 > 2 > 1. However, bromocoumarins are not fluorescent in THF; thus, CTPEs 1–9 exhibited weak emission in THF with emission occurring at 456, 471, 464, 487, 475, 489, 447, 471, and 471 nm, respectively.
image file: d0nj00037j-f2.tif
Fig. 2 Normalized absorption (top; left to right) in THF solvent and fluorescence (bottom; left to right) spectra in THF/H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v) of CTPEs 1–9 at 25 °C.
Table 1 Photophysical properties of CTPEs 1–9
Compound number λ max (nm) λ em (nm) Stokes shiftaδν (cm−1) Φ F (%) λ em (nm) Φ F (%) λ em (nm) Optical band gapa (eV) Theoretical band gapd (eV)
HOMO LUMO E g
a THF. b THF/H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v). c Solid film. d Calculated at the B3LYP level.
1 312 456 10[thin space (1/6-em)]121 0.06 469 24 468 3.19 5.52 1.86 3.66
2 325 471 9538 0.05 478 21.6 474 3.16 5.43 1.87 3.56
3 348 464 7183 0.12 484 27 476 3 5.44 1.99 3.45
4 350 487 8037 0.01 490 23 490 2.9 5.38 2.11 3.27
5 346 475 7849 0.09 489 16 482 2.95 5.28 1.88 3.40
6 376 489 6146 0.33 495 22 495 2.81 5.31 2.22 3.09
7 338 447 7214 0.01 479 22 474 2.99 5.45 2.15 3.30
8 333 471 8798 0.05 480 22 475 3.1 5.36 1.94 3.42
9 354 471 7017 0.14 483 19 479 2.96 5.40 2.21 3.19


AIEE properties

The AIE properties of CTPEs 1–9 were investigated using fluorescence spectroscopy in a binary solvent system of THF and H2O (Fig. 3–5 and Fig. S20–S28, ESI). CTPEs 1–9 displayed AIE in THF/H2O mixtures. Once the water fraction of the THF/H2O mixture increased from 0 to 80%, CTPEs 1–9 exhibited weak blue-to-green emission in THF; a gradual red shift was observed with no change in fluorescence. However, as the water content increased further to 90% and 99%, CTPEs 1–9 formed insoluble aggregates, thereby enhancing the fluorescence intensity. Notably, emission peaks at 469, 478, 484, 490, 489, 495, 479, 480, and 483 nm are observed for the aggregates of CTPEs 1–9, respectively, in THF/H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v). As similar to the absorption results, CTPEs connected at position C7 of coumarin display red-shifted emission compared to those modified at the C6 and C5 positions; this may be due to from intramolecular charge transfer.38 These data are in good agreement with fluorescence spectra of the corresponding solid films (Fig. S29–S32, ESI). Upon aggregation (THF/H2O, 1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v), CTPEs 1–9 exhibited 645-, 495-, 257-, 160-, 183-, 30-, 179-, 298-, and 105-fold enhancement in fluorescence intensity, respectively, compared to that in THF (Fig. 6). Effect of temperature on the AIE behaviors of CTPEs studied in aggregated state. AIE of CTPEs decreased as the temperature was increased from 4 °C to 65 °C. Upon cooling the CTPEs aggregated solution THF–H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]99 v/v) to 4 °C, aggregation of CTPEs increases and the fluorescence intensity also increased and upon heating the solution to 65 °C, aggregation of CTPEs decreases the fluorescence intensity decreased (Fig. S33–S35, ESI). The effect temperature on AIE can be explained as follows. At low temperature restriction of molecular motions increase and AIE increase and at high temperature restriction of molecular motions decreases and AIE decreases.39
image file: d0nj00037j-f3.tif
Fig. 3 Emission spectra of 1 (λex = 312 nm), 2 (λex = 325 nm) and 3 (λex = 348 nm) (15.75 μM) left to right in THF–H2O mixtures with different volume fractions of water at 25 °C.

image file: d0nj00037j-f4.tif
Fig. 4 Emission spectra of 4 (λex = 350 nm), 5 (λex = 346 nm) and 6 (λex = 376 nm) (14.92 μM) left to right in THF–H2O mixtures with different volume fractions of water at 25 °C.

image file: d0nj00037j-f5.tif
Fig. 5 Emission spectra of 7 (λex = 338 nm), 8 (λex = 333 nm) and 9 (λex = 354 nm) (15 μM) left to right in THF–H2O mixtures with different volume fractions of water at 25 °C.

image file: d0nj00037j-f6.tif
Fig. 6 Plot of fluorescence intensity (I/I0) vs. % of water fraction in THF.

In order to confirm that the enhanced emission observed for CTPEs in THF/H2O with a high water fraction originated from nanoaggregation and to evaluate possible energy sources for the fluorescence, changes in the binary THF/H2O solvent system were investigated using absorption and fluorescence excitation spectroscopy (Fig. S36–S44, ESI). At higher fractions of water (H2O > 80), absorption spectra changed significantly. Broadening and broad/leveled-off tails were observed in the visible region for all CTPEs and were attributed to Mie scattering caused by nanoaggregates.40 CTPE fluorescence excitation spectra in THF and in the THF/H2O mixture correlated with emission spectra in those solvents. Fluorescence excitation bands for CTPEs in the binary THF/H2O solvent system were located at wavelengths correlating to those observed in the corresponding UV-vis absorption spectra.41

The formation of nanoaggregates was further confirmed by scanning electron microscopy (SEM) and DLS (Fig. 7 and Fig. S45–S47, ESI). SEM results clearly indicate the formation of well-defined nanoparticles. In addition, using DLS measurements, average particle sizes (Zave) of 98, 157, 108, 106, 93, 104, 103, 107, and 101 nm were acquired for CTPEs 1–9, respectively. These values confirm that CTPEs 1–9 formed nano-sized particles; this is in good agreement with the SEM and DLS data. The CTPEs 1, 4 and 7 are showing quite different SEM images comparatively with its isomers. This may be due to effect of position and intramolecular interaction between TPE unit and coumarin unit.


image file: d0nj00037j-f7.tif
Fig. 7 FE-SEM images of the fluorescent nanoaggregates of 1–9 in THF/H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]99, v/v; scale bars: 1 μm, respectively).

Time-resolved fluorescence decay profiles of CTPEs were investigated in THF and H2O/THF (99[thin space (1/6-em)]:[thin space (1/6-em)]1 v/v). Time-resolved fluorescence decay curves and fitted decay lifetimes are shown in Fig. S48–S50 (ESI), and Table 2. Time-resolved fluorescence decay curves for CTPEs 1–9 in THF and H2O/THF (99[thin space (1/6-em)]:[thin space (1/6-em)]1 v/v) fit a biexponential decay curve. CTPE lifetimes in THF differ significantly from those observed for aggregated states. The lifetimes of CTPEs 1–9 in THF are 0.3, 0.42, 0.25, 0.43, 0.33, 0.44, 0.64, 0.35, and 0.58 ns, respectively; however, CTPE 1–9 aggregates exhibit average lifetimes of 4.27, 4.58, 2.73, 2.84, 2.89, 3.2, 2.84, 3.46, and 2.29 ns, respectively. The fluorescence lifetimes of CTPE 1–9 aggregates respectively are 14, 10.9, 10.9, 6.6, 8.8, 7.3, 4.4, 9.9, and 3.9, times longer than those of CTPEs in THF. These fluorescence decay results clearly indicate that CTPE aggregates exhibit increased fluorescence compared to those dissolved in THF.

Table 2 Fluorescence lifetimes of CTPEs 1–9 in THF and H2O/THF (99[thin space (1/6-em)]:[thin space (1/6-em)]1 v/v)
THF H2O[thin space (1/6-em)]:[thin space (1/6-em)]THF (99[thin space (1/6-em)]:[thin space (1/6-em)]1 v/v)
Compound number τ 1 (ns) (A1%) τ 2 (ns) (A2%) Average τ (ns) τ 1 (ns) (A1%) τ 2 (ns) (A2%) Average τ (ns)
1 0.305 (94.8) 0.135 (5.2) 0.3 2.18 (53.7) 5.28 (46.3) 4.27
2 0.277 (91.26) 0.9 (8.74) 0.42 2.117 (46.45) 5.418 (53.54) 4.58
3 0.254 (88.9) 0.126 (11.1) 0.25 1.406 (44.2) 3.18 (55.8) 2.73
4 0.23 (88.9) 0.64 (11.1) 0.43 2.33 (78.6) 3.94 (21.4) 2.84
5 0.262 (94.8) 0.786 (5.2) 0.33 1.7 (29.8) 3.17 (70.2) 2.89
6 0.24 (91.9) 0.98 (8.1) 0.44 2.2 (53.3) 3.83 (46.7) 3.2
7 0.277 (94) 1.64 (6) 0.64 1.84 (56) 3.5 (44) 2.84
8 0.279 (94) 0.78 (6) 0.35 1.78 (45.7) 4.05 (54.3) 3.46
9 0.248 (91.2) 1.26 (8.8) 0.58 1.36 (51.5) 2.78 (48.5) 2.29


Theoretical study

In order to understand their structures and electronic properties, density functional theory (DFT) calculations were performed for CTPEs 1–9 and 1-dimer using Gaussian 09 with the 6-31G** basis set for C, N, O, and H at the B3LYP level of theory.42–46 The frontier molecular orbitals of CTPEs 1–9 and 1-dimer are shown in Fig. S51–S53 (ESI). In CTPEs 1–9, the HOMO and LUMO are located on the TPE and coumarin units, respectively. In 1-dimer, the HOMO is majorly located on one molecule TPE unit and LUMO is located on the coumarin unit of other molecule. This observation indicates that charge transfer can occur from the TPE unit to the coumarin unit, which supports the experimental UV-vis and fluorescence data. The theoretical band gaps for CTPEs 1–9 and 1-dimer (calculated at the B3LYP level) are 3.66, 3.56, 3.45, 3.27, 3.40, 3.09, 3.30, 3.42, 3.19 and 3.20 eV respectively (Table 1). The optical band gap values for CTPEs 1–9 are 3.19, 3.16, 3, 2.9, 2.95, 2.81, 2.99, 3.1, and 2.96 eV, respectively.

Conclusions

In summary, a series of CTPE regioisomers with varying position and linkage type were synthesized using Suzuki–Miyaura cross-coupling, Heck coupling, and Sonogashira cross-coupling reactions. The resulting CTPEs were fully characterized using absorption and fluorescence spectroscopy. CTPE derivatives substituted at the C7 position exhibit better electronic communication compared to CTPEs substituted at the C5 and C6 positions. Once aggregated, CTPEs display increased fluorescence lifetimes; this observation further supports AIE in CTPEs. Theoretical DFT calculations were in good agreement with the experimental photophysical results.

Experimental

General methods

All chemicals were purchased from commercial sources and used without further purification. 1H NMR and 13C NMR spectra were recorded on 500 MHz and 125 MHz JEOL, JNM-ECZ 500R/S1 spectrometer. All spectra were recorded at 298 K. 1H NMR data are reported as follows: s: singlet, d: doublet, t: triplet, m: multiplet, with coupling constants, J, given in Hz. Chemical shifts in 1H NMR and 13C NMR spectra are reported in parts per million (ppm) with tetramethylsilane (0 ppm) and CDCl3 (77.00 ppm) as standards. HRMS was recorded on Thermo Fisher Scientific Masstechnik Q Exactive high resolution orbitrap MS. Thin layer chromatography analyses were performed using silica gel 60 F254 plates. UV-vis absorption spectra were measured in various solvents with a UV-vis spectrophotometer (Jasco V-670). Emission spectra were collected using a Hitachi F-7000 fluorescence spectrophotometer. The excitation and emission slits were 5 nm for the emission measurements. Dynamic light scattering (DLS) measurements were conducted using a zeta potential and particle size analyzer (Otsuka ELSZ-2000 series). Field-emission scanning electron microscopy (FE-SEM) images were collected with a FE-SEM Hitachi SU-8010. Time-resolved photoluminescence (TRPL) measurements were carried out using a confocal microscope (Micro time-200, Picoquant, Germany) with a 60× objective. Lifetime measurements were performed at the Korea Basic Science Institute (KBSI, Daegu, Korea). Exponential fitting for the obtained fluorescence decays was accomplished using SymPhoTime-64 software. X-ray diffraction data were obtained at the Korea Basic Science Institute (KBSI, Western Seoul Center, Korea). All measurements were obtained at 298 K. Column chromatography was performed on Merck silica gel (230–400 mesh).

Synthesis

Synthesis of CSTPEs 1–3. 1-(4-Bromophenyl)-1,2,2-triphenylethylene (0.2 g, 0.44 mmol), 10 or 11 or 12 (0.097 g, 0.44 mmol), Pd(PPh3)4 (0.02 g, 4 mol%), and 2 M potassium carbonate solution (3 mL) were dissolved in THF (15 mL). The reaction mixture was left for 12 h under a nitrogen atmosphere at 70 °C. After completion, the reaction mixture was cooled to room temperature and poured into water (50 mL), followed by extraction with ethyl acetate (50 mL) in triplicate. Subsequently, the organic layer was separated and washed with a saturated brine solution. After drying over sodium sulfate (Na2SO4), the solution was concentrated under vacuum. The resulting residue was purified by column chromatography on silica gel with hexane/chloroform (1[thin space (1/6-em)]:[thin space (1/6-em)]9, v/v) as the eluent.
5-(4-(1,2,2-Triphenylvinyl)phenyl)-2H-chromen-2-one, 1. CSTPE 1 was obtained in 64% yield (0.13 g), m.p. 236 °C. 1H NMR (CDCl3, 500 MHz) δ 7.690 (1H, d, J = 10 Hz, aromatic), 7.516 (1H, t, J = 8 Hz, aromatic), 7.302 (1H, d, J = 8.5 Hz, aromatic), 7.208 (1H, dd, J1,2 = 1 Hz, J1–3 = 7.5 Hz, aromatic), 7.154–7.043 (19H, m, aromatic), 6.347 (1H, d, J = 10 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.59, 154.67, 143.86, 143.58, 143.37, 143.32, 141.88, 141.85, 141.40, 140.15, 135.81, 131.57, 131.38, 131.33, 131.3, 131.27, 129, 127.83, 127.74, 127.72, 126.68, 126.66, 125.44, 116.78, 116.16, 115.94. HRMS (ESI-TOF): m/z calculated for C35H25O2 477.1849 [M + H]+, measured 477.1842 [M + H]+.
6-(4-(1,2,2-Triphenylvinyl)phenyl)-2H-chromen-2-one, 2. CSTPE 2 was obtained in 60% yield (0.125 g), m.p. 212 °C. 1H NMR (CDCl3, 500 MHz) δ 7.728–7.685 (2H, m, aromatic), 7.614 (1H, d, J = 2 Hz, aromatic), 7.360–7.317 (3H, m, aromatic), 7.130–7.026 (17H, m, aromatic), 6.440 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.71, 153.34, 143.63, 143.59, 143.57, 143.47, 143.42, 141.49, 140.2, 137.33, 137.02, 132.03, 131.37, 131.34, 131.3, 130.52, 127.81, 127.76, 127.68, 126.59, 126.54, 126.14, 125.78, 118.99, 117.18, 117.01. HRMS (ESI-TOF): m/z calculated for C35H25O2 477.1849 [M + H]+, measured 477.1846 [M + H]+.
7-(4-(1,2,2-Triphenylvinyl)phenyl)-2H-chromen-2-one, 3. CSTPE 3 was obtained in 57% yield (0.118 g), m.p. 215 °C. 1H NMR (CDCl3, 500 MHz) δ 7.699 (1H, d, J = 9.5 Hz, aromatic), 7.496 (1H, s, aromatic), 7.479–7.473 (2H, m, aromatic), 7.38 (2H, d, J = 8.5 Hz, aromatic), 7.140–7.027 (17H, m, aromatic), 6.399 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.90, 154.53, 144.59, 144.31, 143.55, 143.5, 143.07, 141.74, 140.14, 136.75, 132.1, 131.38, 131.34, 131.31, 128.03, 127.85, 127.8, 127.68, 126.69, 126.63, 126.58, 126.38, 123.06, 117.7, 116.21, 114.74. HRMS (ESI-TOF): m/z calculated for C35H25O2 477.1849 [M + H]+, measured 477.1849 [M + H]+.
Synthesis of CDTPEs 4–6. (2-(4-Vinylphenyl)ethane-1,1,2-triyl)tribenzene (0.2 g, 0.56 mmol), 10 or 11 or 12 (0.125 g, 0.56 mmol), Pd(OAc)2 (0.0015 g, 0.0067 mmol), and P(o-tolyl)3 (0.01 g, 0.033 mmol) were dissolved in N,N-dimethylformamide (DMF) (10 mL) and triethylaminetriethylamine (3 mL). The reaction mixture was left for 24 h under a nitrogen atmosphere at 90 °C. After completion, the reaction mixture was cooled to room temperature, followed by evaporation of the solvent. The crude reaction mixture was extracted twice with ethyl acetate (50 mL). Subsequently, the organic layer was separated, washed with saturated brine solution, dried over Na2SO4, and concentrated under vacuum. The resulting residue was purified using column chromatography on silica gel with hexane/chloroform (2[thin space (1/6-em)]:[thin space (1/6-em)]8, v/v) as the eluent.
(E)-5-(4-(1,2,2-Triphenylvinyl)styryl)-2H-chromen-2-one, 4. CSTPE 4 was obtained in 69% yield (193 g), m.p. 262 °C. 1H NMR (CDCl3, 500 MHz) δ 8.084 (1H, d, J = 10 Hz, aromatic), 7.502–7.444 (m, 2H, aromatic), 7.373 (1H, d, J = 16 Hz, aromatic), 7.292–7.221 (3H, m, aromatic), 7.142–6.998 (18H, m, aromatic), 6.427 (1H, d, J = 10 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.48, 154.75, 144.38, 143.64, 143.55, 143.50, 141.57, 140.31, 139.88, 136.48, 134.49, 134.04, 131.91, 131.64, 131.38, 131.36, 131.31, 127.83, 127.77, 127.68, 126.63, 126.62, 126.58, 126.21, 122.23, 121.83, 116.51, 116.16, 115.9. HRMS (ESI-TOF): m/z calculated for C37H26O2 502.1927 [M]+, measured 502.1925 [M + H]+.
(E)-6-(4-(1,2,2-Triphenylvinyl)styryl)-2H-chromen-2-one, 5. CdTPE 5 was obtained in 66% yield (0.185 g), m.p. 240 °C. 1H NMR (CDCl3, 500 MHz) δ 7.687 (1H, d, J = 9.5 Hz, aromatic), 7.635 (1H, dd, J1,2 = 2 Hz, J1–3 = 8.5 Hz, aromatic), 7.505 (1H, d, J = 2 Hz, aromatic), 7.303–7.241 (3H, m, aromatic), 7.128–7.001 (19H, m, aromatic), 6.426 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.61, 153.34, 143.74, 143.69, 143.63, 143.57, 143.53, 141.35, 140.45, 134.73, 134.13, 131.82, 131.39, 131.35, 131.33, 129.61, 129.48, 127.79, 127.73, 127.66, 126.56, 126.51, 126.28, 125.91, 125.34, 119, 117.24, 117. HRMS (ESI-TOF): m/z calculated for C37H26O2 502.1927 [M]+, measured 502.1921 [M + H]+.
(E)-7-(4-(1,2,2-Triphenylvinyl)styryl)-2H-chromen-2-one, 6. CdTPE 6 was obtained in 68% yield (190 g), m.p. 265 °C. 1H NMR (CDCl3, 500 MHz) δ 7.654 (1H, d, J = 9.5 Hz, aromatic), 7.415 (1H, d, J = 8.5 Hz, aromatic), 7.379–7.364 (m, 2H, aromatic), 7.275 (2H, d, J = 8 Hz, aromatic), 7.137–7.006 (19H, m, aromatic), 6.363 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.89, 154.59, 144.28, 143.64, 143.6, 143.51, 143, 141.52, 140.4, 134.41, 131.87, 131.74, 131.4, 131.35, 131.33, 127.99, 127.82, 127.75, 127.67, 126.63, 126.59, 126.56, 126.54, 126.27, 122.51, 118.02, 115.88, 114.11. HRMS (ESI-TOF): m/z calculated for C37H26O2 502.1927 [M]+, measured 502.1923 [M + H]+.
Synthesis of CTTPEs 7–9. (2-(4-Ethynylphenyl)ethane-1,1,2-triyl)tribenzene (0.2 g, 0.56 mmol) and 10 or 11 or 12 (0.125 g, 0.56 mmol), were dissolved in THF/triethylamine (1[thin space (1/6-em)]:[thin space (1/6-em)]1, v/v, 30 mL) and the mixture was deaerated with bubbling nitrogen gas for 10 min. Next, Pd(PPh3)2Cl2 (8 mg, 2 mol%), PPh3 (6 mg, 4 mol%), and CuI (2 mg, 2 mol%) were added. The solution was deaerated for an additional 5 min, and then the reaction was left for 12 h under a nitrogen atmosphere at 60 °C. After completion, the reaction mixture was cooled to room temperature, followed by evaporation of the solvent. The crude product was dissolved in dichloromethane and purified using silica gel column chromatography with hexane/chloroform (2[thin space (1/6-em)]:[thin space (1/6-em)]8, v/v) as the eluent.
5-((4-(1,2,2-Triphenylvinyl)phenyl)ethynyl)-2H-chromen-2-one, 7. CTTPE 7 was obtained in 71% yield (0.2 g), m.p. 239 °C. 1H NMR (CDCl3, 500 MHz) δ 8.19 (1H, d, J = 9.5 Hz, aromatic), 7.47 (1H, m, aromatic), 7.418 (1H, dd, J1,2 = 1 Hz, J1–3 = 7.5 Hz, aromatic), 7.314 (2H, d, J = 8.5 Hz, aromatic), 7.28 (1H, dd, J1,2 = 1.5 Hz, J1–3 = 8.5 Hz, aromatic), 7.147–7.015 (17H, m, aromatic), 6.473 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.54, 154.33, 145.15, 143.47, 143.33, 142.23, 141.87, 140.14, 131.72, 131.49, 131.48, 131.40, 131.22, 128.14, 128.02, 127.97, 127.85, 126.93, 126.86, 126.84, 122.42, 120.04, 119.74, 117.14, 117.06, 96.32, 85.18. HRMS (ESI-TOF): m/z calculated for C37H25O2 501.1849 [M + H]+, measured 501.1849 [M + H]+.
6-((4-(1,2,2-Triphenylvinyl)phenyl)ethynyl)-2H-chromen-2-one, 8. CTTPE 8 was obtained in 68% yield (0.192 g), m.p. 236 °C. 1H NMR (CDCl3, 500 MHz) δ 7.66 (1H, d, J = 9.5 Hz, aromatic), 7.6287.608 (2H, m, aromatic), 7.3017.255 (3H, m, aromatic), 7.1417.01 (17H, m, aromatic), 6.448 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.36, 153.66, 144.57, 143.54, 143.41, 142.93, 142.02, 140.27, 134.94, 131.61, 134.50, 131.47, 131.41, 131.1, 130.86, 127.98, 127.93, 127.83, 126.86, 126.8, 126.78, 120.55, 120.07, 119, 117.55, 117.33, 90.46, 87.87. HRMS (ESI-TOF): m/z calculated for C37H25O2 501.1849 [M + H]+, measured 501.1848 [M + H]+.
7-((4-(1,2,2-Triphenylvinyl)phenyl)ethynyl)-2H-chromen-2-one, 9. CTTPE 9 was obtained in 74% yield (0.206 g), m.p. 224 °C. 1H NMR (CDCl3, 500 MHz) δ 7.63 (1H, d, J = 9.5 Hz, aromatic), 7.3877.372 (2H, m, aromatic), 7.318 (dd, 1H, J1,2 = 1.5 Hz, J1–3 = 8 Hz, aromatic), 7.2567.213 (3H, m, aromatic), 7.256–7.213 (17H, m, aromatic), 6.368 (1H, d, J = 9.5 Hz, aromatic). 13C NMR (CDCl3, 150 MHz) δ 160.58, 153.99, 144.98, 143.53, 143.49, 143.37, 142.93, 142.15, 140.25, 131.65, 131.51, 131.47, 131.42, 131.31, 128, 127.95, 127.84, 127.75, 127.27, 126.92, 126.83, 126.8, 120.25, 119.59, 118.74, 116.96, 93.43, 88.42. HRMS (ESI-TOF): m/z calculated for C37H25O2 501.1849 [M + H]+, measured 501.1845 [M + H]+.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This paper was supported by Konkuk University in 2017.

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Footnote

Electronic supplementary information (ESI) available: General experimental methods, copies 1H NMR and 13C NMR spectra, UV-vis and fluorescence spectra, tables, frontier molecular orbital figures, DFT data, crystallographic data of 1 and CIF files of 1. CCDC 1975276. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/d0nj00037j

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