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Article

Bis(tricyclic) Aromatic Enes That Exhibit Efficient Fluorescence in the Solid State

by
Masaki Shimizu
1,*,
Kenta Nishimura
1,
Mizuki Mineyama
1,
Rin Terao
1,
Tsuneaki Sakurai
1 and
Hiroshi Sakaguchi
2
1
Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology, 1 Hashikami-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
2
Institute of Advanced Energy, Kyoto University, Gokasho, Uji 611-0011, Japan
*
Author to whom correspondence should be addressed.
Molecules 2024, 29(22), 5361; https://doi.org/10.3390/molecules29225361
Submission received: 21 October 2024 / Revised: 9 November 2024 / Accepted: 11 November 2024 / Published: 14 November 2024
(This article belongs to the Special Issue Explorations in Luminescent Molecular Materials)
Browse Figures
Versions Notes

Abstract

:
We report herein that bis(tricyclic) aromatic enes (BAEs) consisting of 6-6-6-membered frameworks such as acridine, xanthene, thioxanthene, and thioxanthene-S,S-dioxide act as a new class of organic luminophores that exhibit blue-to-green fluorescence in the solid state and in polymer film with good to excellent quantum yields. The BAEs were prepared by the palladium-catalyzed double cross-coupling reaction of phenazastannines or 10,10-dimethyl-10H-phenothiastannin with 9-(dibromomethylene)xanthene, 9-(dibromomethylene)thioxanthene, or 9-(dibromomethylene)-9H-thioxanthene-10,10-dioxide. Microcrystals or powder samples of the BAEs exhibited brilliant fluorescence with good to high quantum yields (Φ = 0.45–0.88). Furthermore, more efficient emission of blue-to-green light (Φ = 0.59–0.91) was observed for the BAEs dispersed in the poly(methyl methacrylate) (PMMA) films. Density functional theory (DFT) calculations suggest that the photo-absorption of the (thio)xanthene moiety-containing BAEs proceeds via π–π* transitions, whereas the optical excitation of 10,10-dioxido-9H-thioxanthene moiety-containing BAEs involves an intramolecular charge transfer from the acridine/thioxanthene part to the electron-accepting 10,10-dioxido-9H-thioxanthene moiety.

Graphical Abstract

1. Introduction

Bis(tricyclic) aromatic enes (BAEs) are attracting increasing interest as key frameworks for the development of functional organic materials. This is because BAEs exhibit unique electronic behavior and stimuli-responsiveness originating from their cross-conjugated electronic structures and the flexible conformations of the overcrowded alkene moieties. To date, several types of BAE-based functional materials have been developed that exhibit electrochromism [1,2], mechanochromism [3,4], thermochromism [5,6,7,8,9], charge transport [10,11,12,13,14,15], and photosensitivity [16,17,18,19,20,21,22] (Figure 1). However, there are few BAEs that exhibit efficient fluorescence, be that in a solution, in the solid state, or in a polymer film [23,24,25,26]. Organic luminophores that exhibit efficient solid-state emission are essential for the advancement of organic light-emitting diodes [27,28,29], organic light-emitting field-effect transistors [30,31,32,33], and organic solid-state lasers [34,35,36,37]. Furthermore, luminescent solar concentrators (LSCs) have received renewed attention in the field of renewable energy-generating devices [38,39,40,41,42,43,44]. Since LSCs consist of a transparent polymer waveguide, such as poly(methyl methacrylate) (PMMA), doped with a fluorophore, organic luminophores that exhibit efficient fluorophores in polymer film are very attractive as dopants for LSCs. This presents a significant opportunity to explore and develop highly fluorescent BAEs that efficiently fluoresce in the solid state and in a polymer film, expanding their potential as versatile multifunctional optoelectronic materials.
We previously developed the palladium-catalyzed annulation of phenazastannines with 1,1-dibromoalkenes as a facile method for the synthesis of acridine moiety-containing heteromerous BAEs 1–3 (Figure 2) [45,46,47]. When we monitored the progress of the annulation reaction by thin-layer chromatography (TLC), we realized that the product spots on the TLC plates luminesced brilliantly on irradiation with a UV lamp (365 nm). This observation suggested that the synthesized BAEs 1–3 exhibit solid-state fluorescence and prompted us to investigate their luminescent properties. Herein, we report the single-crystal structures, absorption, and fluorescence properties and theoretical calculations of heteromerous BAEs 1–3 (Figure 2) and demonstrate that they are a promising new class of organic luminophores exhibiting efficient solid-state fluorescence in the blue-to-green region.

2. Results and Discussion

2.1. Synthesis

The preparation of acridine moiety-containing BAEs 1a, 1b, 1c, 2b, and 2c has been reported previously and involves the Pd-catalyzed annulation of phenazastannines with the corresponding 1,1-dibromoalkenes [45]. Using the same protocol, 2a and 3a were synthesized in 56% and 52% yields from 9-(dibromomethylene)xanthene (4) [48] and 10,10-dimethyl-5-methylphenazastannine (5) [49] or 10,10-dimethyl-10H-phenothiastannin (6) [49], respectively (Scheme 1). The annulation of 9-(dibromomethylene)-9H-thioxanthene-10,10-dioxide (7) [45] with 6 afforded 3c in a 56% yield. The decomposition temperatures (Td) of 1–3, at which 5% of the mass was lost, were 291 (1a), 304 (1b), 322 (1c), 278 (2a), 282 (2b), 309 (2c), 256 (3a), and 303 °C (3c), indicating that the BAEs were thermally very stable.

2.2. Single-Crystal Structures

Single crystals of 1a and 3a suitable for X-ray diffraction analysis were obtained by recrystallization from a solution of ethyl acetate and dichloromethane, respectively. CCDC numbers of 1a and 3a are CCDC 2180600 and 2180603. Compound 1a crystallized in the triclinic space group P-1. As shown in Figure 3a,b, the tetraarylated ethene moiety (C2(C4)C1=C6(C7)C9) was flat, having dihedral angles of 0.10° (∠C2–C1–C6–C7) and 1.16° (∠C4–C1–C6–C9). The length of the C1=C6 bond is 1.358 Å, slightly longer than a standard value of the C=C bond (1.34 Å) [50], and the ∠C2–C1–C6, ∠C4–C1–C6, ∠C2–C1–C4, ∠C1–C6–C7, ∠C1–C6–C9, and ∠C7–C6–C9 bond angles are 124.92°, 125.72°, 109.36°, 124.11°, 125.12°, and 110.75°, respectively, which are significantly deviated from the ideal sp2 carbon angle of 120°. The unusual bond angles probably reduced the steric crowding around the tetraarylated ethene moiety. The central six-membered rings of the acridine and xanthene moieties adopted a boat-like conformation. The methoxyphenyl group was almost perpendicular to the acridine moiety, having a dihedral angle of 79.06° (∠C11–N1–C13–C14), suggesting that the N-aryl group did not participate in the conjugated system of the acridine moiety. Probably due to the bent molecular framework, there is no close packing between the BAE cores (Figure 3c), which is an attractive characteristic for the realization of efficient solid-state emissions. Compound 3a crystallized in the orthorhombic space group Pca21. As observed for 1a, the tetraarylated ethene moiety (C2(C4)C1=C6(C7)C9) of 3a was also flat, having dihedral angles of 3.16° (∠C2–C1–C6–C7) and 0.05° (∠C4–C1–C6–C9), and the bond angles at the sp2 carbons differed significantly from 120° (125.37° for ∠C2–C1–C6, 124.72° for ∠C4–C1–C6, 109.88° for ∠C2–C1–C4, 124.05° for ∠C1–C6–C7, 123.58° for ∠C1–C6–C9, and 112.36° for ∠C7–C6–C9) (Figure 3d). The conformations of the pyran and thiopyran rings were characterized as boat conformations (Figure 3e). Each molecule in the crystal forms a loose packing structure, which is advantageous for avoiding concentration quenching in the solid state (Figure 3f).

2.3. Absorption Properties in Toluene

The absorption data and spectra of 1–3 in toluene are shown in Table 1 and Figure 4, respectively. The absorption maxima of 1a, 1b, and 1c are almost the same as those of 2a, 2b, and 2c, respectively, indicating that the nitrogen substituent does not influence the energy gaps between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs). The maxima of 1a–1c and 2a–2c were red-shifted in the order 1b, 1a, 1c, 2b, 2a, and 2c. The maxima of 3a and 3c were significantly blue-shifted compared to those of 1 and 2, which is reasonable considering that the electron-donating nature of a sulfur atom is less than that of a nitrogen atom.

2.4. Fluorescence Properties in Toluene

Toluene solutions of 1–3 were faintly or moderately fluorescent (Table 2). The spectra are shown in Figure 5. The emission maxima of 1a–1c and 2a–2c appeared at 475–494 nm, whereas 3a and 3c fluoresced at 435 and 441 nm. The shorter wavelengths of the emission maxima of 3a and 3c compared to those of 1a–1c and 2a–2c are consistent with the trend in the absorption maxima. In contrast, the fluorescence maxima of 1a and 2a were almost the same as those of 1b and 2b, respectively, which is inconsistent with the absorption data. These results suggest that the electronic structures of the lowest singlet excited states (S1 states) of isolated 1a and 1b as well as 2a and 2b are quite similar (see Theoretical Calculations). Except for those of 1c and 2c (0.04 and 0.06, respectively), the quantum yields of 1–3 in toluene were moderate. Since the radiative decay constants (kr) of 1c and 2c were comparable to those of the others, the primary cause of the very low quantum yields of an SO2 moiety-containing 1c and 2c in toluene is the large nonradiative decay constants (knr) of 32.0 and 23.5, respectively, which are an order of magnitude larger than those of the others (see Table S1 in Supplementary Material).

2.5. Fluorescence Properties in the Solid State

In sharp contrast to the weak fluorescence in toluene, brilliant green fluorescence (λem = 494–568 nm) was observed for the solid samples of 1 and 2. In contrast, 3a and 3c efficiently emitted blue fluorescence at 443 and 448 nm, respectively, in microcrystalline solid form (Figure 6a). The fluorescence data and spectra are summarized in Table 2 and shown in Figure 7. The fluorescence quantum yields were good to excellent (Φ = 0.45–0.88) and were higher than those in toluene, except for that of 2b (Φ = 0.30). Until now, only 0.308 and 0.347 have been reported as solid-state quantum yields of BAEs for 9-(9H-xanthen-9-ylidene)-9H-xanthene [23] and tetrabenzo[5.7]fulvalene [24]. Thus, these results demonstrate that the developed BAEs are a novel class of organic fluorophores that exhibit efficient fluorescence in the solid state [51,52,53,54,55,56,57]. The fluorescence maximum and quantum yield of 2b were 568 nm and 0.30, respectively. Compared to other BAEs, the maximum was significantly red-shifted, and the yield was much lower, suggesting that 2b was densely aggregated in the solid state, and thus, suffered from severe concentration quenching.

2.6. Fluorescence Properties in PMMA Film

We next investigated the fluorescence properties of the BAEs in polymer film to explore their potential as LSC-applicable emitters. First, four polymer films were prepared from PMMA, polystyrene, poly(bisphenol A carbonate), and poly(vinyl acetate) using 1b and 2c as the dopants. The fluorescence spectra were almost the same regardless of the host polymer (Figure S7 for 1b and Figure S8 for 2c). The highest fluorescence quantum yields (0.91 for 1b and 0.80 for 2c) were observed with the PMMA films (the data are shown in Table S2). Therefore, PMMA was chosen as the host polymer and the fluorescence properties of the other BAEs in PMMA were investigated. The fluorescence data and spectra are shown in Table 2 and Figure 8. The films efficiently emitted fluorescence at 429–506 nm, which were like those in the solution case, indicating that each molecule dispersed in the PMMA film was spatially and electronically isolated, as in the solution case. The fluorescence quantum yields in the PMMA film were high to excellent (Φ = 0.59–0.91), probably because of the isolated and rigid environment of each luminophore. Consequently, 1–3 are considered very attractive fluorophores for LSC applications.

2.7. Theoretical Calculations

To gain insight into the electronic structures and photoluminescence mechanisms of 1–3, density functional theory (DFT) calculations of the BAEs were carried out using the Gaussian 09 package [58]. Initially, DFT calculations were performed at the B3LYP/6-31+G(d) level of theory. However, the calculated HOMO–LUMO energy gaps did not correlate well with the experimentally estimated gaps from absorption spectra, suggesting that this functional and basis set combination was inadequate. In contrast, calculations at the B3LYP/cc-pVDZ level of theory yielded results that were consistent with the experimental data, with the exception of 2a. Therefore, we used the B3LYP/cc-pVDZ levels of theory for theoretical calculation study. Initial structures for structural optimization were generated from the single-crystal structures of 1a and 3a. The calculated HOMO and LUMO energies (EHOMO and ELUMO) and their energy gaps (ΔELUMO–HOMO) are summarized in Table 3 along with the experimentally determined HOMO–LUMO gaps (ΔEexp), which were estimated from the absorption maxima in toluene. The magnitude of the relationship between the calculated HOMO–LUMO energy gaps is consistent with that of the experimentally estimated energy gaps except for that of 2a. The discrepancy between the calculated and experimental HOMO-LUMO gaps for compound 2a remains unclear. One possible explanation is the difference in phases: The calculated value is for the gas phase, while the experimental value is for the solution phase. The HOMOs of 1a, 1b, 2a, 2b, and 3a were distributed over the entire BAE framework with a large contribution from the nitrogen and sulfur atoms despite their bent structures (Figure 9). The absence of the HOMOs over the methoxyphenyl group of 1a and 1b is probably due to the perpendicular orientation of the methoxyphenyl group to the BAE plane. The HOMOs of 1c, 2c, and 3c containing an SO2 moiety are localized over the acridine skeleton and the central C=C bond, but not over the SO2 group nor over the two benzene rings bridged by the SO2 group. Meanwhile, the LUMOs of 1a, 1b, 2a, and 2b were delocalized over the BAE skeleton with little or no contribution from the sulfur or nitrogen atom. In the cases of 1c, 2c, and 3c, which contain an SO2 moiety, the LUMOs were mostly accumulated over the 10,10-dioxido-9H-thioxanthene moiety. In short, these orbital distributions suggest that 1a, 1b, 2a, 2b, and 3a are optically excited via the π–π* transitions of the BAE skeletons, while the photoexcitation of 1c, 2c, and 3c occurs through a weak intramolecular charge transfer (ICT) from the acridine/thioxanthene moiety to the electron-accepting 10,10-dioxido-9H-thioxanthene moiety. The Lippert–Mataga plots of 1c and 2c were prepared with seven solvents (CHCl3, Et2O, EtOAc, THF, CH2Cl2, PhCN, and DMF) [59,60,61,62,63]. The plots fit the calibration lines defined by a linear approximation with moderate correlation coefficients of 0.701 and 0.731 (Figures S10 and S12), which experimentally supports ICT as the mechanism for the excitation process of the SO2-containing BAEs.

3. Materials and Methods

3.1. General

Melting and decomposition points were determined with a TG/DTA6200 Seiko Instrument (Seiko Instruments Inc., Chiba, Japan). 1H NMR spectra were recorded with a Varian Mercury 400 (400 MHz) spectrometer (Las Vegas, NV, USA). The chemical shifts of 1H NMR signals are expressed in parts per million, relative to the internal tetramethylsilane standard (δ = 0 ppm) or chloroform (δ = 7.26 ppm). Splitting patterns are indicated as follows: s, singlet; d, doublet; t, triplet; and m, multiplet. 13C NMR spectra were recorded with a Varian Mercury 400 (100 MHz) spectrometer with tetramethylsilane (δ = 0 ppm) or chloroform-d (δ = 77.0 ppm) as internal standard. Chemical shifts are given in parts per million, relative to the internal standards. IR attenuated total reflectance (IR-ATR) spectra were recorded by using a Shimadzu FTIR-8400 spectrometer (Kyoto, Japan) equipped with a Specac® Quest ATR diamond accessory (Pleasantville, NY, USA). Fast atom bombardment high-resolution mass spectrometry (FAB–HRMS) analyses were performed with a JEOL JMS-700 spectrometer (Tokyo, Japan). TLC analyses were performed by using Merck Kieselgel 60 F254 silica plates (Rahway, NJ, USA). Silica gel column chromatography was carried out by using Merck Kieselgel 60 (230–400 mesh). 1,4-Dioxane was distilled from Na before use. All reactions were carried out under argon atmosphere.

3.2. Synthesis

3.2.1. Synthesis of 2a

In a glovebox, 5 (0.25 g, 0.75 mmol), 4 (0.18 g, 0.50 mmol), Pd2(dba)3 (23 mg, 0.025 mmol), PCy3 (28 mg, 0.10 mmol), CsF (0.76 g, 5.0 mmol), and 1,4-dioxane (25 mL) were added to a 50 mL vial. The vial was sealed, removed from the glovebox, and heated at 130 °C for 15 h. The reaction mixture was then filtered through a pad of Celite, and the filtrate was concentrated in vacuo. The crude product was purified using silica gel column chromatography (eluent: hexane/EtOAc 10:1) to give 2a (0.10 g, 0.28 mmol, 56%) as a yellow solid. Tm (dec.) = 328 °C; TLC: Rf 0.40 (hexane/EtOAc 10:1); 1H NMR (CDCl3, 400 MHz): δ = 3.56 (s, 3H), 6.76–6.84 (m, 4H), 7.00 (d, J = 7.6 Hz, 2H), 7.09 (d, J = 7.6 Hz, 2H), 7.14–7.23 (m, 8H); 13C NMR (CDCl3, 100 MHz): δ = 33.4, 112.6, 116.9, 119.7, 120.2, 122.2, 123.8, 125.6 (2C), 127.6, 127.7, 128.0, 128.3, 144.8, 155.6; IR (neat): ν = 2958, 1591, 1550, 1494, 1452, 1433, 1386, 1338, 1288, 1265, 1161, 1134, 1120, 1058, 1028, 879, 844, 754, 742, 700 cm−1; HRMS (FAB) m/z [M+] calcd for C27H19NO: 373.1467, found: 373.1459.

3.2.2. Synthesis of 3a

The same procedure for the synthesis of 2a was applied to 4 and 6, affording 3a in 52% yield as a colorless solid. Tm (dec.) = 295 °C; TLC: Rf 0.25 (hexane); 1H NMR (CDCl3, 400 MHz): δ = 6.77–6.78 (m, 4H), 7.01 (t, J = 7.6 Hz, 2H), 7.11 (d, J = 7.6 Hz, 2H), 7.15–7.23 (m, 6H), 7.58 (d, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz): δ = 116.7, 122.3, 123.9, 124.0, 126.0, 126.7, 127.8, 128.4, 128.8, 129.3, 130.3, 136.5, 136.7, 154.8; IR (neat): ν = 3913, 3709, 3616, 3564, 3047, 2349, 1579, 1556, 1467, 1435, 1394, 1373, 1238, 1228, 1195, 1095, 1062, 1026, 945, 883, 839, 790, 742, 727, 698 cm−1; HRMS (FAB) m/z [M+] calcd for C26H16OS: 376.0922, found: 376.0918.

3.2.3. Synthesis of 3c

The same procedure for the synthesis of 2a was applied to 6 and 7, affording 3c in 56% yield as a colorless solid. Tm (dec.) = 366 °C; TLC: Rf 0.25 (hexane/EtOAc 10:1); 1H NMR (CDCl3, 400 MHz): δ = 6.89 (d, J = 7.6 Hz, 2H), 6.98 (t, J = 7.6 Hz, 2H), 7.07 (d, J = 7.6 Hz, 2H), 7.14–7.22 (m, 4H), 7.37 (t, J = 7.6 Hz, 2H), 7.59 (d, J = 7.6 Hz, 2H), 8.08 (d, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz): δ = 124.0, 126.1, 127.2, 127.5, 127.6 (2C), 130.2, 130.2, 130.8, 134.6, 135.2, 137.1, 138.7, 139.1; IR (neat): ν = 1454, 1437, 1311, 1294, 1267, 1165, 1141, 1116, 1066, 1049, 742, 723, 688 cm−1; HRMS (FAB) m/z [M+] calcd for C26H16O2S2: 424.0592, found: 424.0602.

3.3. X-Ray Crystallography of Single Crystals

Data were measured on a Bruker (Bremen, Germany) SMART APEX diffractometer (MoKa radiation, l = 0.71073 Å) at 300 K. The structures were solved by direct methods using SHELXTL programs (ver 6.1) and refined with full-matrix least-squares on F2. CCDC numbers of 1a and 3a are CCDC 2180600 and 2180603.

3.4. Preparation of Doped PMMA Films

The sample (1 mg) was dissolved in a CH2Cl2 (1 mL) solution of PMMA (99 mg). The resulting solution was dropped onto a quartz plate (10 mm × 10 mm) and spin-coated at 300 rpm for 40 s and then at 1000 rpm for 60 s. The deposited film was dried at room temperature in air for 12 h and under reduced pressure for 6 h.

3.5. Measurement of Absorption and Photoluminescence Spectra

The spectroscopic-grade toluene for photoluminescence measurements was purchased from Kanto Chemical Co., Inc. (Tokyo, Japan) and degassed with argon before use. The absorption spectra were obtained using a Shimadzu UV-2550 spectrometer. The fluorescence spectra and absolute quantum yields were recorded using a calibrated integrating sphere with a Hamamatsu Photonics C9920-02 Absolute PL Quantum Yield Measurement System (Hamamatsu, Japan), and the fluorescence lifetimes were measured with a Hamamatsu Photonics Quantaurus-Tau.

4. Conclusions

We demonstrated that heteromerous BAEs consisting of two different tricyclic moieties (in this study, acridine, xanthene, thioxanthene, or thioxanthene-S,S-dioxide) are thermally very stable, adopt bent conformations, and efficiently fluoresce in the solid state in the blue-to-green region. As summarized in Figure 10, the fluorescence quantum yields in the solid state, especially in PMMA film form, were good to excellent and significantly higher than those in the toluene solution. Given that to date there have been no reports of BAEs exhibiting solid-state emissions with high efficiency (Φ > 0.40), this study represents the first demonstration of BAEs that are highly luminescent in the solid state and add solid-state luminescent properties to the material functions exhibited by BAEs. We hope that the findings of this study will encourage materials chemists and scientists to use BAEs as solid-state fluorescent materials.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules29225361/s1, Figures S1–S6: 1H and 13C NMR spectra of 2a, 3a, and 3c; Figure S7: Fluorescence spectra of 1b in polymer film; Figure S8: Fluorescence spectra of 2c in polymer film; Figure S9: Absorption and fluorescence spectra of 1c in various solvents; Figure S10: Lippert–Mataga plots of 1c; Figure S11: Absorption and fluorescence spectra of 2c in various solvents; Figure S12: Lippert–Mataga plots of 2c; Table S1: Fluorescence data of 1, 2, and 3; Table S2: Fluorescence data of 1b and 2c in polymer films; Table S3: Orientational polarizability (Δf), wavelength of absorption maximum (λabs), wavelength of fluorescence maximum (λF), wave number of absorption maximum (νa), wave number of fluorescence maximum (νF), and Stokes shift (νa–νF) of 1c; Table S4: Orientational polarizability (Δf), wavelength of absorption maximum (λabs), wavelength of fluorescence maximum (λF), wave number of absorption maximum (νa), wave number of fluorescence maximum (νF), and Stokes shift (νa–νF) of 2c.

Author Contributions

Conceptualization, M.S.; methodology, M.S.; validation, M.S., K.N., M.M., R.T., T.S. and H.S.; formal analysis, M.S. and T.S.; investigation, M.S., K.N., M.M., R.T. and T.S.; resources, H.S.; data curation, M.S.; writing—original draft preparation, M.S.; writing—review and editing, M.S., T.S. and H.S.; visualization, M.S. and T.S.; supervision, M.S.; project administration, M.S.; funding acquisition, M.S. and H.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by ZE Research Program, IAE (Kyoto University), grant numbers ZE2021A-29 and ZE2022A-27.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in the Supplementary Materials.

Acknowledgments

The NMR and MS measurements were performed with research equipment shared via the MEXT Project for promoting the public utilization of advanced research infrastructure (Program for supporting the introduction of the new sharing system; Grant Number JPMXS0421800221).

Conflicts of Interest

The authors declare no conflict of interest.

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Molecules 29 05361 g001
Figure 1. Examples of functional bis(tricyclic) aromatic enes (BAEs).
Figure 1. Examples of functional bis(tricyclic) aromatic enes (BAEs).
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Figure 2. Molecular structures of heteromerous BAEs 1–3.
Figure 2. Molecular structures of heteromerous BAEs 1–3.
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Scheme 1. Synthesis of 2a, 3a, and 3c (conditions: Pd2(dba)3 (5 mol%), PCy3 (20 mol%), CsF (10 eq), and 1,4-dioxane, 130 °C).
Scheme 1. Synthesis of 2a, 3a, and 3c (conditions: Pd2(dba)3 (5 mol%), PCy3 (20 mol%), CsF (10 eq), and 1,4-dioxane, 130 °C).
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Figure 3. (a) Top view of the molecular structure of 1a. (b) Side view of the molecular structure of 1a. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å], angles [°], and dihedral angles [°]: C1–C6 1.358 Å, ∠C2–C1–C6 124.92°, ∠C4–C1–C6 125.72°, ∠C2–C1–C4 109.36°, ∠C1–C6–C7 124.11°, ∠C1–C6–C9 125.12°, ∠C7–C6–C9 110.75°, ∠C2–C1–C6–C7 0.10°, ∠C4–C1–C6–C9 1.16°, and ∠C11–N1–C13–C14 79.06°. (c) Crystal structure of 1a [space group: P-1; unit cell dimensions: a = 8.3291(9), b = 10.3629(12), c = 15.2598(17), α = 107.212(2), β = 94.588(2), and γ = 108.454(2)]. Each molecule in packing diagram is color-coded by symmetry equivalence. (d) Top view of the molecular structure of 3a. (e) Side view of the molecular structure of 3a. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] angles [°], and dihedral angles [°]: C1–C6 1.346 Å, ∠C2–C1–C6 125.37°, ∠C4–C1–C6 124.72°, ∠C2–C1–C4 109.88°, ∠C1–C6–C7 124.05°, ∠C1–C6–C9 123.58°, ∠C7–C6–C9 112.36°, ∠C2–C1–C6–C7 3.16°, and ∠C4–C1–C6–C9 0.05°. (f) Crystal structure of 3a [space group: Pca21; unit cell dimensions: a = 18.282(2), b = 5.4902(7), and c = 18.355(2)]. Each molecule in the packing diagram is color-coded by symmetry equivalence.
Figure 3. (a) Top view of the molecular structure of 1a. (b) Side view of the molecular structure of 1a. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å], angles [°], and dihedral angles [°]: C1–C6 1.358 Å, ∠C2–C1–C6 124.92°, ∠C4–C1–C6 125.72°, ∠C2–C1–C4 109.36°, ∠C1–C6–C7 124.11°, ∠C1–C6–C9 125.12°, ∠C7–C6–C9 110.75°, ∠C2–C1–C6–C7 0.10°, ∠C4–C1–C6–C9 1.16°, and ∠C11–N1–C13–C14 79.06°. (c) Crystal structure of 1a [space group: P-1; unit cell dimensions: a = 8.3291(9), b = 10.3629(12), c = 15.2598(17), α = 107.212(2), β = 94.588(2), and γ = 108.454(2)]. Each molecule in packing diagram is color-coded by symmetry equivalence. (d) Top view of the molecular structure of 3a. (e) Side view of the molecular structure of 3a. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] angles [°], and dihedral angles [°]: C1–C6 1.346 Å, ∠C2–C1–C6 125.37°, ∠C4–C1–C6 124.72°, ∠C2–C1–C4 109.88°, ∠C1–C6–C7 124.05°, ∠C1–C6–C9 123.58°, ∠C7–C6–C9 112.36°, ∠C2–C1–C6–C7 3.16°, and ∠C4–C1–C6–C9 0.05°. (f) Crystal structure of 3a [space group: Pca21; unit cell dimensions: a = 18.282(2), b = 5.4902(7), and c = 18.355(2)]. Each molecule in the packing diagram is color-coded by symmetry equivalence.
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Figure 4. Absorption spectra of 1–3 in toluene.
Figure 4. Absorption spectra of 1–3 in toluene.
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Figure 5. Fluorescence spectra of 1–3 in toluene.
Figure 5. Fluorescence spectra of 1–3 in toluene.
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Figure 6. Fluorescence images of 1–3 in the solid state (a) and in PMMA films (b) upon irradiation with a UV lamp (365 nm).
Figure 6. Fluorescence images of 1–3 in the solid state (a) and in PMMA films (b) upon irradiation with a UV lamp (365 nm).
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Figure 7. Fluorescence spectra of 1–3 in the solid state.
Figure 7. Fluorescence spectra of 1–3 in the solid state.
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Figure 8. Fluorescence spectra of 1–3 in PMMA film.
Figure 8. Fluorescence spectra of 1–3 in PMMA film.
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Figure 9. HOMO and LUMO drawings of 1–3.
Figure 9. HOMO and LUMO drawings of 1–3.
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Figure 10. Graphical summary of the fluorescence quantum yields of 1–3.
Figure 10. Graphical summary of the fluorescence quantum yields of 1–3.
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Table 1. Absorption data of 1–3 in toluene.
Table 1. Absorption data of 1–3 in toluene.
Compλmax (nm) aε (M−1 cm−1) b
1a40634,100
1b39611,600
1c4198300
2a40513,800
2b39616,100
2c41922,500
3a35613,700
3c3598000
a λmax: absorption maximum. b ε: molar absorption coefficients.
Table 2. Fluorescence data of 1–3 in toluene, in the solid state, and in PMMA film.
Table 2. Fluorescence data of 1–3 in toluene, in the solid state, and in PMMA film.
CompIn Toluene aIn the Solid State bIn PMMA c
λem dΦ eτ fλem dΦ eτ fλem dΦ eτ f
1a4750.201.35200.815.924780.815.49
1b4760.321.94940.674.424760.915.56
1c4930.040.35130.764.954960.824.87
2a4780.372.45190.456.224840.846.52
2b4780.483.25680.306.494780.915.98
2c4940.060.45210.675.345060.805.95
3a4350.321.84430.884.664290.674.02
3c4410.402.24480.603.544370.594.13
a Excitation wavelengths [nm]: 405 for 1a and 2a, 396 for 1b and 2b, 420 for 1c and 2c, 355 for 3a, and 325 for 3c. b Powder: 1a, 1b, 2b, and 2c; microcrystalline solid: 1c, 2a, 3a, and 3c. Excitation wavelength [nm]: 405 for 1a, 396 for 1b, 420 for 1c, 405 for 2a, 396 for 2b, 420 for 2c, 355 for 3a, and 325 for 3c. c Excitation wavelength [nm]: 405 for 1a, 396 for 1b, 380 for 1c, 405 for 2a, 396 for 2b, 420 for 2c, 355 for 3a, and 325 for 3c. d λem: fluorescence maximum [nm]. e Φ: fluorescence quantum yield. f τ: fluorescence lifetime [ns].
Table 3. HOMO and LUMO energies of 1–3 a.
Table 3. HOMO and LUMO energies of 1–3 a.
CompEHOMO [eV]ELUMO [eV]ΔELUMO−HOMO [eV]ΔEexp [eV] b
1a−4.96−1.453.513.05
1b−5.05−1.403.653.13
1c−5.45−2.053.402.96
2a−5.21−1.473.743.06
2b−5.10−1.423.683.13
2c−5.58−2.153.432.96
3a−5.54−1.673.873.48
3c−5.94−2.073.873.45
a Calculated at the B3LYP/cc-pVDZ levels. b ΔEexp: HOMO–LUMO energy gaps estimated from the absorption maxima in toluene.
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Shimizu, M.; Nishimura, K.; Mineyama, M.; Terao, R.; Sakurai, T.; Sakaguchi, H. Bis(tricyclic) Aromatic Enes That Exhibit Efficient Fluorescence in the Solid State. Molecules 2024, 29, 5361. https://doi.org/10.3390/molecules29225361

AMA Style

Shimizu M, Nishimura K, Mineyama M, Terao R, Sakurai T, Sakaguchi H. Bis(tricyclic) Aromatic Enes That Exhibit Efficient Fluorescence in the Solid State. Molecules. 2024; 29(22):5361. https://doi.org/10.3390/molecules29225361

Chicago/Turabian Style

Shimizu, Masaki, Kenta Nishimura, Mizuki Mineyama, Rin Terao, Tsuneaki Sakurai, and Hiroshi Sakaguchi. 2024. "Bis(tricyclic) Aromatic Enes That Exhibit Efficient Fluorescence in the Solid State" Molecules 29, no. 22: 5361. https://doi.org/10.3390/molecules29225361

APA Style

Shimizu, M., Nishimura, K., Mineyama, M., Terao, R., Sakurai, T., & Sakaguchi, H. (2024). Bis(tricyclic) Aromatic Enes That Exhibit Efficient Fluorescence in the Solid State. Molecules, 29(22), 5361. https://doi.org/10.3390/molecules29225361

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