Fluorescein-Bridged Perylene Bisimide Dimer for Use as Liquid Crystal: Studies on Mesomorphic and Fluorescence Properties

doi:10.21203/rs.3.rs-297853/v1

PDF

Research Article

Fluorescein-Bridged Perylene Bisimide Dimer for Use as Liquid Crystal: Studies on Mesomorphic and Fluorescence Properties

https://doi.org/10.21203/rs.3.rs-297853/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 02 Aug, 2021

Read the published version in Journal of Fluorescence →

You are reading this latest preprint version

A novel fluorescein-bridged perylene bisimide (PBI) dimer for liquid crystal (LC) with geometrically symmetric structure was developed. The mesomorphic results indicated that the energetically stable and unstable conformers of fluorescein fragments could lead to the transformation of mesophases from a hexagonal columnar mesophase to an uncertain phase at 136.9 °C in heating, whilst a stable hexagonal columnar mesophase maintained between 175.6 °C and 58.6 °C in cooling. The selectively excited fluorescence characters in THF solution demonstrated that the fluorescence resonance energy transfer (FRET) effect between fluorescein fragments and PBI unites could provide a means to effectively impose strong fluorescence of the dimeric PBIs modified with suitable chromophore at the N-imide position, which alternatively serves as a platform for the further study of multi-functional PBI-based LCs.

Health Economics & Outcomes Research

perylene bisimide

liquid crystal

fluorescein

FRET

fluorescence

Boasting the natural virtues of fascinating photophysical properties (e.g., longer excitation wavelength, high fluorescence quantum yield, long fluorescence lifetime, and the stability to light and thermal-exposure), perylene bisimide (PBI) is a recurring and overwhelming motif in various fields of solar photovoltaics[1-4], organic electronic devices[5,6], photoelectrocatalysis[7], photoisomerization[8], near-infrared photothermal conversion[9], phosphorescence[10], moisture detection[11], bioimaging[12,13], theranostics[14,15], and biosensing/bioassay[16]. Additionally, the self-assembled π-π interaction of perylene core plays a decisive role in its functional characteristic and renders it possible to develop various supramolecular species involving host-guest recognition[17,18], gelator[19-21], LCs[22], and so on. On account of 1D charge transport pathways in supramolecular columnar mesophase, discotic PBI-based LCs can be used to fabricate thin semiconducting devices over large areas[23-25]. In fact, bringing the discotic PBI-based LCs more closely to practical applications requires excellent mesomorphic and emission properties. Up to now, although a plenty of discotic PBI-based LCs were achieved using various mesomorphic groups such as triphenylene[26-30], cholesterol[31,32], siloxane[33], dendritic peptides[34], cyclotetrasiloxane[35], oligosiloxane[36], polyhedral oligosilsesquioxane (POSS)[37], and gallic acid derivatives[38-42], most of their fluorescence emission were regulated and managed by substituted groups through the intramolecular charge-transfer (ICT) and/or π-extended conjugation system. While hardly affecting the alteration of emission peak, the substituents at the N-imide positions can weaken the fluorescence because of the photoinduced electron transfer (PET)[22], which limit the practical application of the fluorescent PBI-based LCs in photoelectronic and electroluminescent devices. Thus, to realize the modulation of excited fluorescence of PBIs, modification at the N-imide positions is crucial for development of novel functional LCs.

In order to construct discotic PBI-based LCs, it had been reported that the integration of the perylene core into six peripheral alkyl chains could effectively control over molecular alignment for fabricating a stable hexagonal columnar mesophase[43,44]. On the other hand, a large number of researches have focused the attention on the study and development of some polyploid PBIs for new materials[2,4,45-51]. Unfortunately, a previously reported exploration on the dimeric PBI-based LCs focused on functionalization with two PBI units through different length of poly methylene spacer at the N-imide position, which has a distinctive feature of little changed emission in free solution state according to Kasha’s rule[50]. However, how to trigger changes in emission properties of dimeric PBI-based LCs with suitable substitution at the N-imide position still remains difficult.

In this work, in terms of the enhanced fluorescence originating from FRET effect of bis-chromophoric groups[42,44], a novel fluorescein-bridged PBI dimer for LC was firstly synthesized as shown in Scheme 1. The target PBI 3 exhibited different LC behaviors due to the presence of fluorescein unit, while the emission spectrum of PBIs in THF solution could be improved by transferring the energy from fluorescein fragment to PBI core. This study was an innovative approach to demonstrate the methodology on building two different chromophores functionalized LCs.

Materials and Equipments

Acetonitrile (MeCN 98%, Alfa Aesar) was dried over P₂O₅ under a nitrogen atmosphere and distilled before use. The anhydrous potassium carbonate (K₂CO₃) was prepared in a muffle furnace at 400 °C for 12 h. All other commercially purchased chemicals were used without further purification. Column chromatographic separation was performed on silica gel (200–300 mesh). Thin-layer chromatography (TLC) was performed on glass plates precoated with silica gel. All proton nuclear magnetic resonance (¹H and ¹³C NMR) spectra were conducted with a Bruker-ARX 400 spectrometer in CDCl₃ solvent, and calibrated using tetramethylsilane (TMS, δ = 0 ppm) as internal standard. Chemical shifts were quoted in parts per million (ppm), and coupling constants were made out as J-values in Hz. MALDI-MS spectrum was determined on a Bruker MALDI-Mass spectrometer. Fourier transform infrared (FT-IR) spectra were measured on Perkin Elmer Spectrum 100 FT-IR spectrometer with solid KBr pellets. DSC measurements were determined in a hermetic aluminium pan using a thermal analyzer (Q100) at a scanning rate of 5 °C min^-1 from -30 °C to 270 °C under a nitrogen atmosphere. The mesomorphic texture of the sample was captured with a polarization optical microscope (Leica DMRX), operated with a temperature-controlled heating setup (Linkam THMSE 600). The mesomorphic structure of the sample was carried out by XRD measurement using an X-ray diffractometer (XRD7, SEIFERT-FPM), equipped with Cu Kα radiation (λ = 1.54056 Å) at 40 kV and 30 mA. UV-visible absorption spectrophotometer (Shimadzu, UV-2550) and fluorescence spectrophotometer (Shimadzu, RF-5301PC) were employed to investigate the photophysical properties of the sample. Experimentally, the emission spectra of the samples were recorded in THF (10 μM solutions) using 1 cm quartz cuvette, when slit widths were Δλ_ex = 3 nm and Δλ_em = 5 nm, respectively. The fluorescence absolute quantum yields (Φ_F) were measured on an Edinburgh Instruments FLS920 fluorescence spectrometer with a calibrated integrating sphere.

Synthesis of fluorescein-bridged perylene bisimide dimer 3

Under a nitrogen atmosphere, PBI intermediate (compound 2) (1.29 g, 0.8 mmol), and fluorescein (0.14 g, 0.4 mmol) were placed into a suspension of anhydrous K2CO3 (0.14 g, 1 mmol) in 35 mL of anhydrous MeCN. The mixture was refluxed in 18 h under magnetically stirring condition. Reaction was monitored by TLC. As completion of the reaction, the mixture was cooled to room temperature, the excess solvent was then evaporated under reduced pressure. After admixing with 30 mL of HCl solution (1 M), the resulting mixture was extracted with 40 mL of DCM. The organic phase was washed with brine (3 × 30 mL), dried over anhydrous MgSO4, filtered, and concentrated with a rotary evaporator to afford a red residue. The residue was further purified by a silica gel column (DCM/petroleum ether (2:1, v/v)) to give compound 3 as a red solid in yield of 70%. FT-IR (KBr), ν/cm^-1: 1698, 1660 (C=O); ¹H NMR (400 MHz, CDCl₃) δppm: 8.20 (bs, 8H, Per-H), 7.54 (d, J = 8.0 Hz, 2H, Flu-H), 7.36 (s, 2H, Flu-H), 7.19 (bs, 16H, Ar-H), 7.15-7.12 (m, 4H, Flu-H), 7.00 (s, 2H, Flu-H), 6.84 (bs, 16H, Ar-H), 4.92 (s, 2H, OCH2CO), 4.31 (m, 2H, FluOCH2CO), 4.09 (t, J = 8.0 Hz, 8H, NCH₂), 3.61 (t, J = 8.0 Hz, 4H, OCH₂), 1.68-0.86 (m, 214H, CH₂ and CH₃); ¹³C NMR (100 MHz, CDCl3) δppm: 167.12, 165.53, 163.93, 161.59, 160.66, 159.43, 157.44, 155.97, 152.58, 149.61, 147.13, 144.51, 141.33, 137.86, 135.25, 132.73, 128.74, 127.50, 125.93, 122.00, 119.00, 114.00, 110.26, 105.43, 102.44, 100.73, 97.99, 68.20, 65.05, 62.22, 42.61, 31.69, 29.34, 26.19, 24.19, 21.01, 18.76, 14.84; anal. Calcd for C₂₂₈H₂₈₀N₄O₂₅: C, 78.77; H, 8.12; N, 1.61. Found: C, 79.01; H, 8.10; N, 1.68. MALDI-MS (C₂₂₈H₂₈₀N₄O₂₅) [M]⁺: calcd: m/z = 3476.08. found: m/z = 3476.24.

Synthesis and characterization

Fluorescein, as a highly preferable fluorescent chromophore, has been widely applied for biological assays as well as biolabeling due to its exceptional fluorescence properties[52-59], whereas little attention was paid to disk-like LCs of fluorescein. In our previous studies, designing and controlling the effect of a rigid chromophore building block into the columnar mesophase architectures could ensure the mesomorphic nature to optimize photophysical properties, which provided an approach for the design of multifunctional LC materials[60, 61]. With a view to the stiff planar quinoid scaffold of fluorescein as well as the extraordinary mesogenic properties of PBI 1, the dimeric PBI-based LC 3 was constructed by inserting a fluorescein unite between two PBIs 1 at the N-imide position. The straightforward one-step synthetic route for the dimeric PBI-based LC 3 is illustrated in Scheme 1. With the key intermediate PBI 1 in hand,[44] PBI 3 was easily prepared by nucleophilic substitution of PBI 1 with fluorescein. In the presence of K₂CO₃, the red solid of final compound 3 was obtained by refluxing compound 1 and 2 in MeCN with a yield of 70%. To check the solubility of compound 3, it was dissolved in different organic solvents including chloroform, dichloromethane (DCM), Toluene, THF and DMF. Compound 3 exhibited relatively good solubility in chloroform, dichloromethane and THF.

The chemical structure of target compound 3 was fully characterized by various characterization techniques (NMR, MALDI-MS, FT-IR and elemental analysis), and the results fitted well to the expected structure. ¹H NMR spectrum and the details of other characterization spectra were listed in the Supporting Information. In Figure S1, one can the clear splits for aromatic proton of fluorescein units but broad signals for aromatic protons of nonylphenoxy and perylene skeleton. After examining the proton signals of same skeleton of compound 3, its precursor 1 and reference compounds 4 and 5, we noticed all of them showed the broad signals for the H_a, H_b and H_c[43, 44]. The phenomena suggested that this kind of broad signals for the H_a, H_b and H_c could be ascribed to internal structural features for these compounds. By analysing this structural feature, it could be observed that the aromatic ring away from perylene skeleton (such as fluorescein unit in compound 3) can rotate freely around the single bond due to the small steric resistance, resulting in the clear splits for protons. However, due to the big steric resistance and the long alkyl chains on nonylphenoxy units, the rotation of nonylphenoxy units on perylene skeleton was limited and slow, resulting in compound 3 adopted various conformations which possessed different intersection angles between nonylphenoxy units and perylene skeleton. The signals of H_a, H_b and H_c in Figure S1 were the overlapped and mixed signals of H_a, H_b and H_c in different conformation and changing spatial orientation of compound 3. Thus, the broad signals for H_a, H_b and H_c were observed. On the other hand, the specific protons of OCH₂CO, FluOCH₂CO and OCH₂ function groups established self-governed chemical shifts at 4.92 (g), 4.31 (f), and 3.61 (e) ppm, respectively. The relative integrals of all peaks agree with the number for protons. Therefore, the well-defined target compound 3 was successfully obtained with good purity.

Mesomorphic studies

To evaluate the mesomorphic properties, the basically recognized results of the thermal phase transition temperatures and enthalpies of the target PBI 3 with differential scanning calorimetry (DSC) were presented in Figure 1, quoting the first cooling and second heating runs to erase the thermal history. The relevant data were summarized in Table 1. Subsequently, the mesomorphic birefringence textures from the crossed polarizing optical microscope (POM) of specimen were observed in the heating-cooling cycles as displayed in Figure 2. During second heating process, the mesomorphic properties of PBI 3 exhibited three endothermic peaks for three transitions, which were subjected to the crystal-LC (61.3 °C), LC-LC (136.9 °C), LC-isotropic (182.2 °C) transitions. This was further supported by the observation of LC textures. Upon heating from the melting temperature at a rate of 2.0 °C min^-1, intriguing pseudo-focal conical fan-shaped textures with a large area of homeotropic alignment domains for the column stacks were observed in the temperature range from 61 ℃ to 137 ℃. Figure 2(a) was captured at 95 ℃ and consistent with the images of the monomeric PBI-based LCs with multistrand peripheral alkyl chains [40]. From Figure 1 and Table 1, a comparative study of the involved PBIs revealed that the mesomorphic phase of PBI 3 occurred at 61.3 °C well above its analogues PBI 4 (46.8 °C) and PBI 5 (56.2 °C) in the course of heating. Such thermotropic behavior was attributed to the rigid structure of fluorescein group needing more energy cost to melt. Moreover, In comparison with PBIs 4 and 5, PBI 3 had a higher clearing temperature at 182.2 °C and a wider mesomorphic temperature range of ~120 °C. Notably, there was an endothermic peak for LC-LC (136.9 °C) transition in heating trace, suggesting the mesophase changed from one phase to another formation. As shown in Figure 2(b), a temperature rise induced dramatic changes, giving the randomly oriented textures from 137 °C to 182 °C. Figure 2b was pictured at 158 °C in heating. This observation leads to the conclusion that a separation of the metastable mesophase occurred at 136.9 °C (ΔH = 4.7 kJ mol^-1) because the fluoresceine fragment were dispersed within the mobile aliphatic chains rather than in the perylene stacks. In addition, another transformation peak of LC-isotropic was observed at 182.2 °C, the POM image of PBI 3 changed into a dark field as the temperature exceeding the clear point (182 °C) in the heating process.

Table 1 Transition temperatures (°C) and enthalpies ΔH (kJ mol^-1) of target compound 3, reference compounds 4 and 5.
PBIs.	Phase transitions^[a][°C (kJ mol^-1)]
3	Cr 61.3 (9.2) → Col_h136.9 (4.7) → Col 182.2 (11.5) → Iso Iso 175.6 (9.6) → Col_h58.6 (10.3) → Cr

4^[^b]	Cr 46.8 (12.6) → Col_h155.7 (21.4) → Iso Iso 144.7 (20.5) → Col_h42.0 (8.3) → Cr

5^[^c]	Cr 56.2 (16.84) → Col_h106.5 (10.36) → Iso Iso 157.3 (11.18) → Col_h49.6 (17.35) → Cr
[a] Cr = crystalline, Col_h = hexagonal columnar mesophase, Col = columnar mesophase, Iso = isotropic. [b] The data are cited from ref. [43]. [c] The data are cited from ref. [44].

Nevertheless, the mesomorphic properties of PBI 3 exhibited two exothermic peaks for two transitions in DSC cooling cycle, which were subjected to the isotropic-LC (175.6 °C), LC-crystal (58.6 °C) transitions. When the sample was cooled from the isotropic liquid state at a rate of 2.0 °C min^-1, the single mesophase was maintained in the whole DSC cooling curve and stable up to the crystallization of PBI 3 (58.6 °C), and there was no significant phase transition below the crystallized peak. PBI 3 cooled from the isotropic melt until a fully developed LC texture was observed under POM at approximately 175 °C. The mass-produced pseudo-focal conical fan-shaped textures as well as optically isotropic homeotropic domains for PBI 3 were observed between 175 °C and 58 °C in cooling process, which well agreed with the observed result in DSC. Figure 2c was captured at 142 °C in the cooling-down stage, and it represented the POM texture within a temperature range from 175 °C to 58 °C in cooling, similar to the one observed at 95 °C in the heating (Figure 2a). PBI 3 exhibited the two double reversible humps of crystalline-mesophase and mesophase-isotropic transitions appearing at around melting point and clearing point in DSC curves, respectively. The reversible transition temperatures in the cooling-down stage were below the relative temperatures in heating, known as the hysteresis, referring to the formation of LC germs at lower temperature on cooling. As a consequence, the detailed analysis of mesomorphic properties with a combination of DSC and POM confirmed that fluorescein-bridged perylene dimer 3 hold a stable columnar mesophase between 175.6 °C and 58.6 °C in cooling, while it had two kinds of mesophases with a mesomorphic temperature range of ~120 °C in heating. Insufficiently, more information on the stacked structure of PBI 3 in mesophase could not be obtained via DSC and POM means.

With the comprehensive understanding on the mesomorphic properties via DSC and POM means, we further lucubrated the theoretical packing parameters of LC 3 by variable-temperature XRD measurements at a rate of 2 °C /min under the first cooling and second heating runs. The XRD traces were carried out in Figure 3. The relevant data were summarized in Table 2. In Figure 3(a), the sample heated at 68 °C shows two diffraction peaks at 2θ = 3.84° and 2θ = 25.87° owing to the self-assembly by halves. In heating, both of Figure 3(b) and (c) exhibit that there is a sharp scattering peak (75 ℃, 2θ = 3.84°; 95°, 2θ = 3.84°) along with two weak peaks (75 ℃, 2θ = 6.70° and 7.44°; 95 ℃, 2θ = 6.69° and 7.45°) in the small-angle region, respectively. The calculated d-spacings of 22.99 Å, 13.18 Å, and 11.87 Å at 75 ℃ and 22.99 Å, 13.20 Å, and 11.86 Å at 95 ℃, confirmed the interplanar d-spacing ratio of 1:1/√3:1/√4 for the [d₁₀₀], [d₁₁₀] and [d₂₀₀] planes in a columnar hexagonal mesophase. In the wide-angle region, a broad diffuse halo at 2θ = 15-30° arising from the molten alkyl chains and a subtle reflection peak at approximately 2θ = 25.80° (3.44 Å) corresponding to the π-π stacking distance of the closest PBI cores for [d₀₀₁] plane were clearly observed at both 75 ℃ and 95 ℃ in heating. Based on these reflections, the observed textures (Figure 2(a)) and DSC data, it proves strongly the existence of the columnar hexagonal mesophase with a temperature range from 61 °C to 137 °C on heating.

Table 2 Summary of the structural information and lattice parameters in mesophases for LC 3 (derived from variable-temperature XRD diffraction experiments)
T [℃].	Cycle state	Phase^[a]	d₁₀₀[Å]	α^[b][Å]	c^[c] [Å]
68	heating	Col_h	22.99	26.55	3.44
75	heating	Col_h	22.99	26.55	3.43
95	heating	Col_h	22.99	26.55	3.45
158	heating	U	/	/	/
142	cooling	Col_h	22.87	26.41	3.44
[a] Col_h = hexagonal columnar mesophase, U = uncertain mesophase; [b] α = √(4/3 × d2 100); [c] Intracolumnar layer spacing c [Å].

However, only one reflection at 2θ = 2.10° (42.04 Å) in the low-angle region was monitored in heating, and it even remained unchanged in the temperature range from 137 °C to 182 °C. Figure 3(d) was recorded at 158 ℃ in heating. By comparison to the diffraction profiles of samples at 75 ℃ and 95 ℃ in heating (Figures 3(b) and (c)), no more scattering information was acquired in Figure 3(d). Thus, the mesophase model for LC 3 was ill-defined with raising the temperature from 137 ℃ to 182 ℃ upon second heating, which was consistent with the results of DSC and POM measurements from 137 ℃ to 182 ℃ upon second heating. This observation also indicated that the fluorescein fragment dispersed within the mobile aliphatic chains rather than in the perylene stacks. On the other hand, when the sample was annealed from the isotropic liquid state at a rate of 2.0 °C min^-1, only one XRD pattern was measured during 175 °C to 58 °C in cooling process and the XRD trace (Figure 3(e)) at 142 °C served as representative. The dominating d-spacing ratio of the [d₁₀₀] (2θ = 3.86°, 22.87 Å), [d₁₁₀] (2θ = 6.68°, 13.22 Å) and [d₂₀₀] (2θ = 7.44°, 11.87 Å) planes were also 1:1/√3:1/√4, similar to the scattering peaks in figures 3(b) and (c). This observation indicated that a columnar hexagonal mesophase could be processed over a broad temperature range from 175 °C and 58 °C on cooling. Moreover, the 2D correlation of a columnar hexagonal mesophase is again present in cooling process. This could be explained that the molecular motion of PBI 3 was reduced and the fluorescein fragment dispersed within the mobile aliphatic chains rather than in the perylene stacks. In addition, the average lattice parameter (α = 26.48 Å) of LC 3 nears the space length (~ 29.54 Å) between PBI core and fluorescein fragment (furnished with Chem 3D Pro 17 software from Cambridge Soft). Taking together with the results of DSC, POM and XRD experiments, the integration of PBI-fluorescein-PBI 3 made a hexagonal columnar model from 61 to 137 ℃ in heating as well as a broad temperature range of 117 ℃ in cooling, whilst the mesophase model could not be ascertained between 137 ℃ and 182 ℃ in heating. Due to the orderless dispersion of fluorescein might influence on the ordered columnar hexagonal mesophase of perylene skeleton and resulted in the imperfect XRD diffraction model for mesophase of compound 3, the signals of XRD diffraction became broad than that of normal perylene liquid crystals (as shown in Figure 3).

Photophysical properties

The photophysical properties of PBI 3 were investigated by the UV-vis absorption and fluorescence spectra. The solvent effect for absorption and fluorescence spectra of PBI 3 was demonstrated in Figure S5 and S6, respectively (see the ESI†). The mirror-image symmetry could be observed between the emission and absorption spectra in various organic solvents (10 μM solutions). On account of the excellent fluorescence of PBI 3 in THF solvent, THF was chosen for exploring efficiently the emission behaviour of PBI 3. To compare the photophysical properties of PBI 1, PBI 3, and fluorescein raw material, their absorption and emission spectra, measured within 5 min of dispersing them in THF solvent (10 μM), were presented in Figure 4 and 5, respectively. The relevant data was summarized in Table 3. In Figure 4, the absorption spectrum of fluorescein raw material exhibits two distinctive peaks at 456 and 485 nm in the range of 400- 500 nm due to its lactone and quinoid structures. When compared to the spectrum of PBI 1 with three symbolic bands of 0-2, 0-1, and 0-0 transitions positioned at 446, 534, and 575 nm, the absorption spectrum of PBI 3 exhibits the similar signature of perylene core and the unchanged absorption maxima. Whereas the absorption band of PBI 3 at around 446 nm exhibited a considerably improved profile, the absorbance intensity ratios of peak at 575 nm to that at 446 nm in the absorption spectra of PBI 1 was higher than that of PBI 3. The ratio values were 2.33 and 1.45 for PBI 1 and PBI 3, respectively. These results indicated that the absorption of PBI 3 overlaps the absorption of fluorescein fragment in the range of 400-500 nm, and that no electronic coupling existed between PBI chromophores and fluorescein fragment in the ground state.

Table 3 Photophysical properties of PBI 3, PBI 1, and fluorescein 2 in solution (10 μM)
Compd.	λ_abs (nm)	λ_em (nm)	Stokes shift nm (cm^-1)	τ_f^[a] (ns)	τ_f^[b](ns)	Φ_f ^[a]	Φ_f ^[b]
1	575	616	41 (1158)	2.89	2.90	0.35	0.80
2	456/485	540	55 (2100)	/	/	/	/
3	572	616	44 (1249)	3.27	3.03	0.86	0.74
[a] Excited at 450 nm in THF solution; [b] Excited at 550 nm in THF solution.

As shown in Figure 5, the emission spectrum of fluorescein raw material displayed a band at 540 nm (λ_ex= 450 nm). PBI 1 had an emission peak concentrated at 616 nm (λ_ex= 550 nm). The fluorescence spectrum of target PBI 3 also exhibited a peak at 616 nm (λ_ex= 550 nm) due to the substitution at N-imide positions of the PBI core. When selectively excited at λ_ex= 450 nm for efficient excitations of the PBI chromophores and fluorescein fragment, the emission spectrum of PBI 3 just showed an enhanced band located at 616 nm, where the intensity was 1.5-fold higher than that of the substantial excitation of PBI 3 at λ_ex= 550 nm, indicating the intramolecular FRET between the PBI chromophores and fluorescein fragment as excited at 450 nm.

Moreover, the fluorescence quantum yield (Φ_f) of PBI 3 is 0.86 and 0.74 (in Table 3) when selectively excited at 450 nm and 550 nm in pure THF solution, respectively. It should be noted that, when excited at 550 nm in pure THF solution, the fluorescence quantum yield (Φ_f) of PBI 3 is 0.74, matching rather closely with those of PBI 1 (0.80). However, when excited at 450 nm in pure THF solution, the fluorescence quantum yield (Φ_f) of PBI 3 exhibits remarkable value of 0.86 relative to PBI 1 (0.35), which is further supported by the intramolecular FRET between the PBI chromophores and fluorescein segment as excited at 450 nm. Similarly, the principle of FRET also greatly affects the fluorescence lifetime τ_f (ns) of PBI 3. The τ_f value of PBI 3 (3.27) is greater than PBI 1 (2.89) as excited at 450 nm. The above discussion demonstrated that the PBI 3 showed different fluorescence specificities due to the intramolecular FRET between the PBI chromophores and fluorescein fragment when the fluorescein fragment was excited at 450 nm. On the other hand, probably because PBI 3 was reciprocally intertwined with a complicated aggregation, the very weaken fluorescence intensity of PBI 3 was detected in solid state. The proposed FRET mechanism for PBI 3 was described in Figure 6.

A novel well-defined perylene liquid crystal with two mesogenic PBIs unit and one fluorescein unit linked by soft spacers at the N-imide position, was successfully obtained and well characterized by NMR, FT-IR, elemental analyses, and MALDI-MS. The mesophase model of target LC was determined to form a hexagonal columnar mesophase and an uncertain phase in heating. The hexagonal columnar mesophase existed stably from 175.6 °C to 58.6 °C on cooling. The fluorescence intensity of PBI 3 excited at 450 nm was 1.5-fold higher than that of the substantial excitation of PBI 3 at 550 nm, giving possible strategy to enhance fluorescence via FRET effect for PBI-based LC.

Acknowledgements We are grateful for the National Natural Science Foundation of China (No: 21406036), Fujian Science, Technology Project (No. 2019N0010) and the Key Research Program in Neijiang Normal University (2020).

Authors’ Contributions M. Z.: experiments and data treatment; M. C.: synthesis of the target compound; H. G.: some measurements of fluorescence and mesomorphic properties; F. Y.: study design and writing of the manuscript.

Funding The study was supported by the National Natural Science Foundation of China (No: 21406036), Fujian Science, Technology Project (No. 2019N0010) and the Key Research Program in Neijiang Normal University (2020).

Data Availability All the data and materials from this manuscript will be made available on request.

Compliance with Ethical Standards

Competing Interests No potential conflict of interest was reported by the authors.

Ethical Approval Not applicable.

Zou D, Yang FF, Zhuang QX et al (2019) Perylene diimide-based electron-transporting material for perovskite solar cells with undoped poly(3-hexylthiophene) as hole-transporting material. ChemSusChem 12:1155- https://doi.org/10.1002/cssc.201802421
Duan YW, Xu XP, Yan H et al (2017) Pronounced effects of a triazine core on photovoltaicperformance-efficient organic solar cells enabledby a PDI trimer-based small molecular acceptor. Adv Mater 29:1605115. https://doi.org/10.1002/adma.201605115
Dayneko SV, Hendsbee AD, Welch GC (2018) Combining facile synthetic methods with greenerprocessing for efficient polymer-perylene diimide basedorganic solar cells. Small Methods 2:1800081. https://doi.org/10.1002/smtd.201800081
Duan YW, Xu XP, Li Y et al (2017) Chalcogen-atom-annulated perylene diimide trimers forhighly efficient nonfullerene polymer solar cells. Macromol Rapid Commun 38:1700405. https://doi.org/10.1002/marc.201700405
Gupta RK, Dey A, Singh A et al (2019) Heteroatom bay-annulated perylene bisimides: New materials for organic field effect transistors. ACS Appl Electron Mater 1:1378- https://doi.org/10.1021/acsaelm.9b00004
Matussek M, Filapek M, Gancarz P et al (2018) Synthesis and photophysical properties of new perylene bisimide derivatives for application as emitting materials in OLEDs. Dyes Pigments 159:590- https://doi.org/10.1016/j.dyepig.2018.07.006
Miao H, Yang J, Peng GL et al (2019) Enhancement of the degradation ability for organic pollutants via thesynergistic effect of photoelectrocatalysis on a self-assembled perylenediimide (SA-PDI) thin film. Sci Bull 64:896- https://doi.org/10.1016/j.scib.2019.05.006
Zhu MG, Guo HY, Cai KC et al (2017) Novel fluorescence-enhancing effect based on light-induced E/Z isomerization of perylenediimides with Schiff-base groups on bay-positions. Dyes Pigments 140:179- https://doi.org/10.1016/j.dyepig.2017.01.048
Lü BZ, Chen YF, Li PY et al (2019) Stable radical anions generated from a porousperylenediimide metal-organic framework forboosting near-infrared photothermal conversion. Nat Commun 10:767. https://doi.org/10.1038/s41467-019-08434-4
Schulze M, Steffen A, Würthner F (2015) Near-IR phosphorescent ruthenium(II) and iridium(III) perylene bisimide metal complexes. Angew Chem Int Ed 54:1570- https://doi.org/10.1002/anie.201410437
Wang Z, Wang G, Chang X et al (2019) A perylene bisimide-contained molecular dyad with high-efficient charge separation: Switchability, tunability, and applicability in moisture detection. Adv Funct Mater 29:1905295. https://doi.org/10.1002/adfm.201905295
You SS, Cai Q, Zheng Y et al (2014) Perylene-cored star-shaped polycations for fluorescent genevectors and bioimaging. ACS Appl Mater Interfaces 6:16327- https://doi.org/10.1021/am5045967
Makkad SK, Asha SK (2017) π-Conjugated chromophore incorporated polystyrene nanobeads as single optical agent for three-channel fluorescent probe in bioimaging application. ACS Biomater Sci Eng 3:1788- https://doi.org/10.1021/acsbiomaterials.7b00259
Sun PF, Yuan PC, Wang GN et al (2017) High density glycopolymers functionalized perylene diimidenanoparticles for tumor-targeted photoacoustic imaging andenhanced photothermal therapy. Biomacromolecules 18:3375- https://doi.org/10.1021/acs.biomac.7b01029
Kim YO, Park SJ, Jung BY et al (2018) Solid-phase synthesis of peptide-conjugated perylene diimidebolaamphiphile and its application in photodynamic therapy. ACS Omega 3:5896- https://doi.org/10.1021/acsomega.8b00040
Song Y, Zhang W, He S et al (2019) Perylene diimide and luminol as potential-resolvedelectrochemiluminescence nanoprobes for dual targetsimmunoassay at low potential. ACS Appl Mater Interfaces 11:33676- https://doi.org/10.1021/acsami.9b11416
Sethy R, Kumar J, Métivier R et al (2017) Enantioselective light harvesting with perylenediimide guests on self-assembled chiral naphthalenediimide nanofibers. Angew Chem Int Ed 56:15053- https://doi.org/10.1002/anie.201707160
Spenst P, Würthner F (2015) A perylene bisimide cyclophane as a “turn-on” and “turn-off” fluorescence probe. Angew Chem Int Ed 127:10303- https://doi.org/10.1002/ange.201503542
Würthner F, Bauer C, Stepanenko V et al (2008) A black perylene bisimide super gelator with anunexpected J-type absorption band. Adv Mater 20:1695- https://doi.org/10.1002/adma.200702935
Han DX, Han JL, Huo SW et al (2018) Proton triggered circularly polarized luminescence in orthogonal- and co-assemblies of chiral gelators with achiral perylene bisimide. Chem Commun 54:5630- https://doi.org/10.1039/C8CC02777C
Görl D, Soberats B, Herbst S et al (2016) Perylene bisimide hydrogels and lyotropic liquidcrystals with temperature-responsive color Chem Sci 7:6786-6790. https://doi.org/10.1039/C6SC02249A
Würthner F, Thalacker C, Diele S et al (2001) Fluorescent J-type aggregates and thermotropic columnar mesophases of perylene bisimide dyes. Chem Eur J 7:2245- https://doi.org/10.1002/1521-3765(20010518)7:10<2245::AID-CHEM2245>3.0.CO;2-W
Eccher J, Zajaczkowski W, Faria GC et al (2015) Thermal evaporation versus spin-coating: Electrical performance incolumnar liquid crystal OLEDs. ACS Appl Mater Interfaces 7:16374- https://doi.org/10.1021/acsami.5b03496
Gupta RK, Sudhakar AA (2019) Perylene-based liquid crystals as materials for organic electronics applications. Langmuir 35:2455- https://doi.org/10.1021/acs.langmuir.8b01081
Funahashi M (2014) Nanostructured liquid-crystalline semiconductors – a new approach to soft matter electronics. J Mater Chem C 2:7451- https://doi.org/10.1039/C4TC00906A
Kong X, Gong H, Liu P et al (2018) Synthesis and investigation on optoelectronic properties of mesogenic triphenylene–perylene dyads linked by ethynylphenyl bridges. New J Chem 42:3211-3221. https://doi.org/10.1039/C7NJ04328G
Guo HY, Zhu MG, Wang ZS et al (2016) Triphenylene–perylene–triphenylene triads with bay-substituents:synthesis, mesomorphism, and electron transfer properties. Tetrahedron Lett 57:4191-https://doi.org/10.1016/j.tetlet.2016.08.004
Xiao Y, Su X, Sosa-Vargas L et al (2016) Chemical engineering of donor–acceptor liquid crystalline dyads and triads for the controlled nanostructuration of organic semiconductors. CrystEngComm 18:4787-4798. https://doi.org/10.1039/C6CE00365F
Lee KJ, Woo JH, Xiao YM et al (2016) Structure-charge transfer property relationship inself-assembled discotic liquid-crystalline donor–acceptor dyad and triad thin films. RSC Adv 6:57811- https://doi.org/10.1039/C6RA08039A
Zhao KQ, An LL, Zhang XB et al (2015) Highly segregated lamellocolumnar mesophase organizationsand fast charge carrier mobility in new discotic donor–acceptor Chem Eur J 21:10379-10390. https://doi.org/10.1002/chem.201500889
Zhu MG, Guo HY, Yang FF et al (2016) Novel room-temperature perylene liquid crystals: synthesis of 1,7-dibrominatedcholesterol–perylene bisimides with different ester-bridging chains and theirmesomorphic properties. Liq Cryst 43:1875- https://doi.org/10.1080/02678292.2016.1218073
Zhu MG, Guo HY, Yang FF et al (2017) Synthesis, mesomorphic and photophysicalproperties of novel triads and pentads of peryleneliquid crystals with cholesterol units at the bay-position. RSC Adv 7:4320- https://doi.org/10.1039/C6RA27003D
Zhang TJ; Sun DM; Ren XK et al (2013) Synthesis and properties of siloxane modified perylene bisimide discotic liquid crystals. Soft Matter 9:10739- https://doi.org/10.1039/C3SM52054D
Gao BX, Xia DF, Zhang LC et al (2011) Helical columnar liquid crystals based on dendritic peptides substituted perylene bisimides. J Mater Chem 21:15975- https://doi.org/10.1039/C1JM13144C
Funahashi M, Yamaoka M, Takenami K et al (2013) Liquid-crystalline perylene tetracarboxylic bisimide derivatives bearing cyclotetrasiloxane moieties. J Mater Chem C 1:7872- https://doi.org/10.1039/C3TC31567C
Zeng Y, Lu L, Gao T et al (2018) Synthesis, helical columnar liquid crystalline structure, and chargetransporting property of perylene diimide derivative bearing oligosiloxaneDyes Pigments 152:139-145. https://doi.org/10.1016/j.dyepig.2018.01.048
Ben HJ, Ren XK, Song B et al (2017) Synthesis, crystal structure, enhanced photoluminescence properties and fluoride detection ability of S-heterocyclic annulated perylene diimide-polyhedral oligosilsesquioxane dye. J Mater Chem C 5:2566- https://doi.org/10.1039/C6TC05171E
Hecht M, Schlossarek T, Stolte M et al (2019) Photoconductive core-shell liquid‐crystals of a perylene bisimide J-aggregate donor-acceptor dyad. Angew Chem Int Ed 58:12979- https://doi.org/10.1002/anie.201904789
Meng L, Wu QM, Yang FF et al (2015) Novel room-temperature thermotropic liquid crystals: Synthesis and mesomorphism of gallic-perylene-gallic trimers. New J Chem 39:72- https://doi.org/10.1039/C4NJ00993B
Zhu MG, Chen YZ, Guo HY et al (2018) Perylene liquid crystals with multiple alkyl chains: investigation of the influence of peripheral alkyl chain number on mesomorphic and photophysical properties. New J Chem 42:8998-https://doi.org/10.1039/C8NJ00480C
Zhu MG, Guo HY, Yang FF et al (2016) Novel perylene liquid crystals: Investigation of the influence ofbay-substituents on mesomorphism and photophysical property. Dyes Pigments 133:387- https://doi.org/10.1016/j.dyepig.2016.06.021
Zhu MG, Zhuo YZ, Cai KC et al (2017) Novel fluorescent perylene liquid crystal with diphenylacrylonitrilegroups: Observation of a large pseudo stokes shift based on AIE andFRET effects. Dyes Pigments 147:343- https://doi.org/10.1016/j.dyepig.2017.08.027
Zhu MG, Zhuo YZ, Guo HY et al (2018) Enhanced fluorescence in both solution and solid state for perylene liquidcrystals with six peripheral alkyl substituents on 1,6,7,12-bay positions andimides positions. J Lumin 194:264- https://doi.org/10.1016/j.jlumin.2017.10.049
Zhu MG, Chen YX, Zhang XY et al (2018) Perylene bisimide with diphenylacrylonitrile onside-chain: strongly fluorescent liquid crystal withlarge pseudo Stokes shift based on AIE and FRET Soft Matter 14:6737-6744. https://doi.org/10.1039/C8SM01183D
Hippius C, van Stokkum IHM, Zangrando E et al (2008) Ground- and excited-state pinched cone equilibria in calix[4]arenes bearing twoperylene bisimide dyes. J Phys Chem C 112:14626- https://doi.org/10.1021/jp804068b
Qu JF, Mu Z, Lai HJ et al (2018) Effect of the molecular configuration of perylene diimide acceptorson charge transfer and device performance. ACS Appl Energy Mater 1:833- https://doi.org/10.1021/acsaem.7b00277
Petrella A, Cremer J, Cola LD et al (2005) Charge transfer processes in conjugatedtriarylamine-oligothiophene-perylenemonoimide dendrimers. J Phys Chem A 109:11687- https://doi.org/10.1021/jp0510995
Sinks LE, Rybtchinski B, Iimura M et al (2005) Self-Assembly of photofunctional cylindrical nanostructures basedon perylene-3,4:9,10-bis(dicarboximide). Chem Mater 17:6295- https://doi.org/10.1021/cm051461s
Zhao Z, Gao SM, Zheng XY et al (2018) Rational design of perylenediimide-substitutedtriphenylethylene to electron transporting aggregation-induced emission luminogens (AIEgens) with highmobility and near-infrared emission. Adv Funct Mater 28:1705609. https://doi.org/10.1002/adfm.201705609
Prajitha KP, Asha SK (2016) The synthesis and structural characterization of twin liquid crystalline perylenebisimides. New J Chem 40:8471- https://doi.org/10.1039/C6NJ00524A
Lin X, Hirono M, Seki T et al (2013) Covalent modular approach for dimension-controlled self-organization ofperylene bisimide dyes. Chem Eur J 19:6561- https://doi.org/10.1002/chem.201300039
Kobayashi T, Urano Y, Kamiya M et al (2007) Highly activatable and rapidly releasable caged fluorescein derivatives. J Am Chem Soc 129:6696- https://doi.org/10.1021/ja070376d
Zhang RL, Zhao J, Han GM et al (2016) Real-time discrimination and versatile profiling of spontaneous reactive oxygen species in livingorganisms with a single fluorescent probe. J Am Chem Soc 138:3769- https://doi.org/10.1021/jacs.5b12848
Hammers MD, Taormina MJ,Cerda MM et al (2015) A bright fluorescent probe for H₂S enables analyte-responsive, 3D imaging in live zebrafish using light sheet fluorescence microscopy. J Am Chem Soc 137:10216- https://doi.org/10.1021/jacs.5b04196
Lv J, Wang F, Qiang J et al (2017) Enhanced response speed and selectivity of fluorescein-based H₂S probe via the cleavage of nitrobenzene sulfonyl ester assisted by ortho aldehyde groups. Biosens Bioelectron 87:96- https://doi.org/10.1016/j.bios.2016.08.018
Urano Y, Kamiya M, Kanda K et al (2005) Evolution of fluorescein as a platform for finely tunablefluorescence probes. J Am Chem Soc 127:4888- https://doi.org/10.1021/ja043919h
Ogasawara H, Grzybowski M, Hosokawa R et al (2018) A far-red fluorescent probe based on a phospha-fluorescein scaffold for cytosolic calcium imaging. Chem Commun 54:299- https://doi.org/10.1039/C7CC07344E
Fan T, Shi R, Tang H, Guo H et al (2020) First fluorescein liquid crystals: synthesis, mesomorphic and fluorescence properties of fluorescein-triphenylene dimers. Liq Cryst 47:1762-1771. https://doi.org/10.1080/02678292.2020.1725986
Guang SY, Tian JC, Wei G et al (2017) A modified fluorescein derivative with improved water-solubility for turn-onfluorescent determination of Hg²⁺ in aqueous and living cells. Talanta 170:89- https://doi.org/10.1016/j.talanta.2017.03.108
Guo HY, Lin LB, Qiu JB et al (2017) Phenylacrylonitrile-bridging triphenylene dimers:The columnar liquid crystals with high fluorescencein both solid state and solution. RSC Adv 7:53316- https://doi.org/10.1039/C7RA10218F
Fang XT, Guo HY, Yang FF et al (2017) Near-infrared fluorescent and columnar liquidcrystal: synthesis, and photophysical andmesomorphic properties of triphenylene-Bodipy-triphenylene triad. RSC Adv 7:23657- https://doi.org/10.1039/C7RA00982H

PDF

Journal Publication

published 02 Aug, 2021

Read the published version in Journal of Fluorescence →

Editorial decision: Accept for Publicaton Pending Revisions
05 Jul, 2021
Reviews received at journal
17 Apr, 2021
Reviewers invited by journal
09 Mar, 2021
Editor assigned by journal
04 Mar, 2021
First submitted to journal
04 Mar, 2021

You are reading this latest preprint version

Fluorescein-Bridged Perylene Bisimide Dimer for Use as Liquid Crystal: Studies on Mesomorphic and Fluorescence Properties

Status:

Journal Publication

Version 1

Abstract

Figures

Introduction

Experimental

Results And Discussion

Conclusion

Declarations

References

Status:

Journal Publication

Version 1