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Abstract
Formation of J-aggregates of the anionic cyanine dye TDBC in a nematic liquid crystal (LC) matrix is reported, with analysis of optical-fluorescent and electro-optical properties of the obtained novel material. The TDBC J-aggregates show a rather long lifetime and high photostability in the nematic matrix. The electro-optical characteristics of the LC matrix are substantially modified, with the Fredericks transition threshold slightly increased, which is, on the other hand, accompanied by the improvement of the optical contrast. Only a minor effect of the forming J-aggregates on the molecular order of the LC structure could be noted.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
In recent years, liquid crystals have been used more and more widely as host matrices for the introduction and dispersion of various inorganic and organic nanoparticles, both in fundamental studies and to obtain new composite nanomaterials [1–6]. In particular, due to the unique combination of optical and anisotropic properties, luminescent liquid crystals (LLCs) are of great interest from the point of view of optoelectronic applications [7–12]. In condensed phases, they can organize with orientational order, leading to, for example, attractive charge transport properties, while they retain fluidity, which provides the self-healing ability and dynamic properties. Furthermore, their anisotropic organization is particularly interesting for applications with polarised light [7–12]. Therefore, polarized radiation based on LLCs has attracted great interest from both scientists and industrialists due to possible applications in optoelectronics, for example as a light source for liquid crystal displays and 3D imaging systems, as well as in the field of medicine, for example, to facilitate chronic pain using near-infrared linearly polarized radiation [7–12]. Another extremely important and relevant area of application of LLCs is the development of liquid crystal micro- and nanolasers, in which significant progress has been observed during the last decade [13–18].
However, traditional LLCs often suffer from fluorescence quenching caused by aggregation, which significantly limits their further use [4]. To overcome this problem, special approaches are used to create complex LC systems, for example, based on luminescent polymer dots covalently linked to the molecules of rod-shaped liquid crystals [19]. Another approach is the use of aggregation-induced emission (AIE), which produces luminescent aggregates with optical properties typical of the solid state, which are not affected by luminescence quenching due to non-radiative energy transfer [20–22].
An important kind of luminescent aggregates are J-aggregates, which are low-dimensional molecular crystals of some types of organic dyes, such as cyanines or perylene derivatives [23,24]. Due to the excitonic nature of their electronic excitations and 1D or 2D structure, the optical properties of J-aggregates differ significantly from the properties of individual molecules or bulk crystals [23–25]. It was shown that they can form liquid crystal (LC) phases, which means that they can be used by themselves to create LLCs with a high degree of anisotropy [26–30]. However, many J-aggregating dyes, like cyanines, have a problem with low photostability, caused, in particular, by interaction with oxygen [23,24,31]. Therefore, the LC phases of these dyes cannot be used for practical applications.
In the work [17], the formation of J-aggregates of perylene dye in the LC matrix was demonstrated. Because of the low permeability and solubility of oxygen in the matrix, a significant increase in the photostability of J-aggregates in LC was obtained. Thanks to this, stimulated emission (laser generation) was obtained for the J-aggregates [17]. Therefore, the J-aggregate dispersions in the LC matrices can become a novel approach for the development of luminescent liquid crystals.
The present article demonstrates the successful formation of J-aggregates of the anionic cyanine dye TDBC in the nematic LC matrix of 5CB with intriguing optical and electro-optical properties of the LLC obtained.
2. Experimental part
TDBC dye (1,1’-disulfobutyl-3,3’-diethyl-5,5’,6,6’-tetrachlorobenzimidazolylcarbocyanine sodium salt, Fig. 1(a)) was purchased from Few Chemicals GmbH (Germany) and used as received. A stock solution of TDBC J-aggregates was obtained by dissolving the dye in doubly distilled water with dye concentrations CTDBC = 10−3 M. As a liquid crystal matrix, we used the nematic liquid crystal 5CB (4-Cyano-4’-pentylbiphenyl, Fig. 1(b)) of 99,5% purity obtained from the Chemical Reagents Plant (Ukraine).
To prepare the J-aggregate dispersions in the 5CB matrix, the TDBC stock solution was rigorously mixed with the liquid crystal in a ratio of 1:99 by volumes giving the final dye concentration CTDBC = 10−5 M and providing a stable and homogeneously colored composition. Larger dye concentrations in the LC lead to precipitation while lesser ones were too low to provide effective J-aggregation with intense J-band.
Fluorescence spectra of solutions were recorded using a spectrofluorimeter Lumina (ThermoScientific, USA) at 530 nm excitation wavelength. Absorption spectra of aqueous solutions in a 1 mm thick quartz cuvette were registered using a USB4000 spectrophotometer (Ocean Optics, USA) supplied with an incandescent lamp. The optical microscope working in the transmitted light mode was used to obtain absorption spectra of thin solid samples. In this case, the light of the microscope halogen lamp was transmitted through the sample (or the glass substrate in the reference measurement) and collected with a 10X/0.50 NA objective. A spectrophotometer USB4000 was connected to ocular lenses with a homemade adapter and used to measure absorption. Such setup ensures good quality spectra for very thin samples.
Fluorescence spectra and photostability of the thin solid samples were measured using a fluorescence microscope MIKMED-2 var.11 (LOMO) equipped with a 10 Mpixels microscope digital camera M3CMOS 10000 (SIGETA, Ukraine) and fiber-optic adapter for micro-spectrometer USB4000. A 450-480 nm band filter filtered excitation and fluorescence was collected in the 520-700 nm spectral range.
Fluorescence lifetimes were measured using a FluoTime 200 (PicoQuant, Germany) system equipped with a 531 nm picosecond pulsed laser diode head. An instrument response function (IRF) width (FWHM) for the whole setup was about 100 ps. The instrument response function was recorded at the excitation wavelength using a dilute solution of Ludox. The fluorescence decays were analysed using the FluoFit software package.
Absolute fluorescence quantum yields were measured by a homemade integrating sphere (diameter 100 mm), which provides a reflectance >99% over the spectral range of 300–1000 nm. The excitation and registration systems were the same as for low-temperature measurements. The absolute quantum yield was calculated using the two-measurement method [32] and correcting for the self-absorption of the fluorescence [33], which is quite significant for J-aggregates because of the very small Stokes shift. The experimental setup was adjusted and tested with rhodamine 6 G (in ethanol, C = 10−5 M, Qlit = 0.9435 [34]) resulting in an accuracy of ± 5% which is typical for such a setup.
E7-12 LCR-meter (KALIBR) was used for electro-optical studies. Sandwich-type LC cells (thickness 20 µm) were used and the sample was introduced between the cell walls using capillary forces. The optical transmission was measured using a UV-2450 spectrophotometer (Shimazu, Japan) within the 190–1100 nm spectral range. The values of optical transmission at λ = 800 nm were considered to be sufficiently far from bands of selective reflection or absorption of the liquid crystalline hosts and the temperature of the sample was stabilized using a flowing-water thermostat (±0.1°C). Phase transition temperatures were determined using differential scanning calorimeter DSC 1 (Mettler-Toledo, Switzerland) from the position of the maximums of the DSC peaks. The measurements were made in the heating mode with the rate of 2 оС/min with a sample mass of 20 mg. Fluorescence polarization measurements were done for the samples in optical LC-cells with planar oriented using spectrofluorimeter Lumina and 15 mm Glan Thompson prism, “UV Grade”, 220-900 nm as polarizers.
3. Results and discussion
TDBC J-aggregates are well-known representatives of the J-aggregate family with well-studied spectroscopic properties and exciton dynamics [35–39]. Our group has experience with TDBC J-aggregates studying in a water solution [40], different polymer films [41,42], and porous TiO2 films [43]. TDBC J-aggregates are formed in water solutions even at quite low dye concentrations such as 10−6 M and reveal a single narrow red-shifted excitonic band, called the J-band [35–43]. For example, at the dye concentration 10−5 M in water solution one could see an intense J-band with maximum λmaxJ = 586 nm and width ΔνFWHM = 430 cm−1 and low-intense monomer band with maximum λmaxmon = 525 nm (Fig. 2(a), curve 1). Another typical feature of J-aggregates is a near-resonant narrow fluorescence band (λmax = 586.5 nm) associated with J-band, while the monomer fluorescence is often absent (Fig. 2(a), curve 2) or very low intensive.
Fig. 2. Absorption (1, blue line) and fluorescence (2, red line) spectra of TDBC J-aggregates in water solution (a) and LC (b). The dye concentrations are 10−5 M. The spectra are normalized for clarity.
Dispersed in the LC matrix, the TDBC J-aggregates reveal similar spectral features; however, the J-band appeared to be much wider (ΔνFWHM = 720 cm−1) preserving its spectral position, and the monomer band is much more intense and slightly red-shifted (λmaxmon = 530 nm) (Fig. 2(b), curve 1). The latter can be explained by the solvatochromism effect [34]. The fluorescence band of TDBC J-aggregates in LC is also slightly red-shifted (λmax = 588 nm) and some shorter-wavelength shoulder with λmax = 547 nm can be found (Fig. 2(b), curve 2), which can be associated with monomer emission.
While J-band and monomer band intensities redistribution can be assigned to some J-aggregate disaggregation in the LC matrix, the J-band width increase is the result of the exciton coherence length decreasing [23–25]. Indeed, it can be estimated as [25]:
However, the fluorescence quantum yield measurements demonstrate an unexpected similarity of the values for TDBC J-aggregates in water and LC, with the one in water (ηwater ∼ 9%) being even less than that in LC (ηLC ∼ 10%). To understand the reason for such the quantum yield growth despite the exciton coherence length decreasing fluorescence decay curves were registered (Fig. 3)
Fig. 3. Fluorescence decays (λreg = 590 nm) for TDBC J-aggregates in water (1) and LC (2). Curve 3 – IRF.
The fluorescence decay for TDBC J-aggregates in LC is much longer (Fig. 3) possessing a lifetime τavLC ∼ 1.19 ns about 10 times larger compared with that in water (τavwater ∼ 0.13 ns). The monomer fluorescence (λmax = 547 nm) is very weak and unlikely can provide a significant contribution to the signal registered at 590 nm. Thus, the nearly 10 times difference in the lifetimes can be associated with the changing in exciton dynamics for TDBC J-aggregates in LC compared with that in water. The main physical properties of the TDBC J-aggregates studied in this work are shown in Table 1, with comparative data for water and LC matrix.
Table 1. A comparative table of TDBC J-aggregates summarises the main characteristics studied in the present work for water and LC matrices
Fluorescence polarization was estimated for the sample with the vertically-oriented director (Fig. 4).
Fig. 4. Vertically (1, red line) and horizontally (2, blue line) polarized fluorescence spectra of TDBC J-aggregates in LC.
Unexpectedly, the perpendicularly polarized fluorescence spectrum (Fig. 4, curve 2) appeared more intense compared to the parallel polarized one (Fig. 4, curve 1) giving the fluorescence anisotropy in the maximum r ∼ –0.05 [34]. If we suppose the TDBC J-aggregates preserve the rod-like morphology found for aqueous solution [40] and the rods oriented vertically along the LC director, the angle of the emission dipole relative to the aggregate axis can be estimated as ∼ 56.6° [34]. Such nontypical orientation of exciton dipole not along the aggregate axis was earlier found for some cylinder-like J-aggregates [23,24]. For a more clear understanding of the J-aggregates orientation in LC and their structure, further experiments are needed along with the modeling.
As the quantum yields are similar, the nearly 10 times difference in the lifetimes is reflected in the same difference in the radiative lifetimes and non-radiative decay rates. While the large increase of the radiative lifetime for the J-aggregates in LC needs to be carefully studied for clear understanding, the non-radiative decay rate decreasing is usually associated with less effective exciton quenching and trapping. The latter can result in the higher photostability of J-aggregates [31]. Indeed, a similar effect we found for J-aggregates of amphi-PIC dye stabilized by serum albumins in a water solution [44]. Measuring the TDBC J-aggregate photostability in the LC matrix we reveal it great improvement compared with that in water (Fig. 5).
Fig. 5. Time dependence of the fluorescence intensity at the band maximum (λreg = 590 nm) for TDBC J-aggregates in water (1) and LC (2) at continuous illumination. The dependences are normalized to the initial values for clarity.
Indeed, while the J-aggregate fluorescence in water nearly completely disappeared after 12 minutes of continuous illumination, in the LC matrix it falls only for 10% after 250 minutes of illumination (Fig. 5). Despite we expected some photostability growth, such great enhancement was unexpected. On one hand, a liquid crystal matrix is known for its weak penetration of molecular oxygen [17], which is one of the main reasons for organic fluorophores photodegradation [31]. On other hand, J-aggregates scarcely produce the triplet states, and the photodegradation mainly takes place from the first excited singlet state [45]. Therefore, the molecular oxygen absence should have less effect on better photostability compared with monomeric fluorophores [31]. Also, the large increase in the J-aggregates’ lifetime in the LC matrix (Fig. 3) should result in less photostability and partially reduce the effect of weak molecular oxygen penetration to LC [31].
Considering the lifetime and quantum yield increase, the possibility of J-aggregates agglomeration needs to be taken into account [46–50]. Indeed, in some cases, the agglomeration leads to larger lifetimes and fluorescence quantum yields and better energy migration [47–49] while in others results in stronger exciton localization causing contrary influence [46,50]. For TDBC J-aggregates in water at a much larger concentration (CTDBC = 10−4 M), where much more efficient J-aggregates agglomeration can be expected, we can find narrower J-band (ΔνFWHM = 360 cm−1), shorter lifetime (τav ∼ 60 ps) and larger fluorescence quantum yield (η ∼ 31%) [40], as compared to the current study. Therefore, the TDBC J-aggregates agglomeration in the LC matrix can be supposed as having rather a small contribution.
Very interesting results were found in [51] concerning TDBC J-aggregates lifetimes and fluorescence quantum yields increasing in blend solutions of water and alkylamines. The changes were explained by the coexistence of nanoscale-sized water and amine domains to restrict the J-aggregate size and solubilize monomers, respectively [51]. However, in our case, the water content (1 vol%) seems to be too small to result in similar effects.
To somehow explain the significant enhancement of the TDBC J-aggregates lifetimes and photostability in the LC matrix, we can only speculate that the 5CB matrix plays a role as an electron donor to the radical cation to suppress the photodegradation similar to [45]. Interestingly, for J-aggregates back electron transfer can be much longer compared with one for monomers [52], which can explain a very larger lifetime for TDBC J-aggregates in LC found in the present research. Further detailed studies are needed to test this hypothesis.
Thus, the dispersion of TDBC J-aggregates in liquid crystal matrix results in their significant spectral changes. It is interesting if it also affects optical and electro-optical properties of the LC matrix. The study by the method of differential scanning calorimetry (DSC) showed the presence of well-defined peaks of the nematic-isotropic transition on the thermograms. One should note a noticeable decrease in the temperature of the nematic-isotropic phase transition Ti for the 5CB systems with J-aggregates (Fig. 6), which can be considered as evidence of intensive interaction of the dopant with LC molecules, violating the orientational order.
The optical transmission spectra show (Fig. 7(a)) that the addition of TDBC J-aggregates to 5СВ decreases the optical transmission of the system. At the same time, we see the J-band of TDBC, which indicates the formation of J-aggregates (and not of H-type aggregations or other interactions of monomers). Moreover, the relative difference in optical transmittance between doped and undoped systems remains unchanged in both physical states, nematic mesophase, and the isotropic phase.
Fig. 7. Optical transmission T as a function of a) wavelength λ for 5CB (1) and 5CB + TDBC J-aggregates (2) at 20 °C and b) temperature t for 5CB (1) and 5CB + TDBC J-aggregates (2) at 800 nm. On inset (a) – the magnified part of the transmission spectrum near the J-band.
The J-band of TDBC J-aggregates is present on the optical transmission spectra (Fig. 7(a), inset) and it shows that TDBC does not affect the optical transmission of the system and therefore has minimal impact on the liquid crystal order since the addition of TDBC at 10−5 M concentration leads to a general decrease of optical transmission by less than 2% in both isotropic and nematic phases (Fig. 7(b)). It should also be noted that introduction of J-aggregates does not lead to substantial increases in the optical transmission jump at the nematic to isotropic transition, unlike many other types of nanoparticles [53,54].
We conducted an additional series of experiments to study the dependence of the optical properties of the 5CB + TDBC system on the concentration of the dye. To exclude possible external influences related to water, we prepared our suspensions by adding the dye directly to the matrix in the form of a dry powder. The results are shown in Fig. 8. It can be noted that at low concentrations of TDBC, the H-aggregates band is observed, which is inherent only in the liquid crystalline phase (Fig. 8(a)) and is completely absent in the isotropic phase (Fig. 8(b)). With increasing TDBC concentration, the J-aggregates band is observed. This band is present in both the mesophase and the isotropic phase. At the same time, the H-aggregates band gradually disappears.
Fig. 8. Optical transmission T as a function of a) wavelength λ for 5CB + TDBC J-aggregates a) at 20 °C (mesophase) and b) at 38 °C (isotope), concentration TDBC from top to bottom: pure 5CB, 10−6 M TDBC, 5 × 10−6 M TDBC, 5х10−5 M TDBC, 5CB + 2х10−5 M TDBC.
In the study of electrical conductivity, the addition of TDBC leads to an increase in the voltage required to induce the Fredericks transition, but it should be noted that this transition is more “sharp” than for the pure matrix, which is seen both by optical (Fig. 9(a)) and electrophysical (Fig. 9(b)) methods.
Fig. 9. Electrical conductivity (a) and optical transmission (b) as a function of applied voltage for 5CB (1) and 5CB + TDBC J-aggregates (2).
If we compare both methods (Fig. 10(a)), we can see that starting with 1.2 volts, the process of electrical conductivity increase has already begun, which indicates some local fluctuations of the director, but the optical transmittance remains unchanged. At the same time for systems with TDBC (Fig. 10(b)), this process is more rapid due to the sharp increase in electrical conductivity, which can potentially lead to an increase in contrast in information display systems using LC electrooptical effects based on Fredericks-type transition [55].
Fig. 10. Optical transmission (1) and electrical conductivity (2) versus voltage for a) 5CB and b) 5CB + TDBC J-aggregates.
4. Conclusions
The stable TDBC J-aggregates dispersion in the 5CB liquid crystal matrix was obtained. The exciton coherence length appeared to be small for the J-aggregates in LC compared with water pointing to a larger statical disorder. Despite it, the fluorescence quantum yield and lifetime grew up demonstrating suppressed non-radiative relaxation and anomaly high radiative lifetime. Additionally, great enhancement of photostability was found, which reason is not clear yet. The addition of TDBC J-aggregates can significantly change the electro-optical properties of the LC-matrix, slightly affecting the molecular order of the LC structure. In particular, the Fredericks transition appeared to be sharper in liquid crystal matrix containing J-aggregates compared with pure LC matrix. The obtained results are promising for development of novel luminescent liquid crystal materials, suggesting ideas for further detailed studies.
Acknowledgments
The authors thank the Armed Forces of Ukraine for the opportunity to prepare the work for publishing. OS expresses sincere gratitude to Dr. Franziska Fennel from the University of Rostock for the invaluable help.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. T. Kato, N. Mizoshita, and K. Kishimoto, “Functional liquid-crystalline assemblies: self-organized soft materials,” Angew. Chem. Int. Ed. 45(1), 38–68 (2006). [CrossRef]
2. J. Prakash, S. Khan, S. Chauhan, and A. M. Biradar, “Metal oxide-nanoparticles and liquid crystal composites: a review of recent progress,” J. Mol. Liq. 297, 112052 (2020). [CrossRef]
3. F. Ahmad, M. Luqman, and M. Jamil, “Advances in the metal nanoparticles (MNPs) doped liquid crystals and polymer dispersed liquid crystal (PDLC) composites and their applications - a review,” Mol. Cryst. Liq. Cryst. 731(1), 1–33 (2021). [CrossRef]
4. R. F. de Souza, S. Zaccheroni, M. Ricci, and C. Zannoni, “Dynamic self-assembly of active particles in liquid crystals,” J. Mol. Liq. 352, 118692 (2022). [CrossRef]
5. A. K. Singh and S. P. Singh, “Revisiting hierarchical arrangement of quantum dots in presence of liquid crystal media,” Mol. Cryst. Liq. Cryst. 746(1), 22–68 (2022). [CrossRef]
6. M. T. Sims, “Dyes as guests in ordered systems: current understanding and future directions,” Liq. Cryst. 43(13-15), 2363–2374 (2016). [CrossRef]
7. Y. Wang, J. Shi, J. Chen, W. Zhu, and E. Baranoff, “Recent progress in luminescent liquid crystal materials: design, properties and application for linearly polarised emission,” J. Mater. Chem. C 3(31), 7993–8005 (2015). [CrossRef]
8. H. Lu, Q. Zhang, J. Sha, M. Xu, J. Zhu, G. Zhang, Y. Ding, and L. Qiu, “Highly polarized absorption and emission from polymer-stabilized smectic guest-host systems,” Liq. Cryst. 46(10), 1574–1583 (2019). [CrossRef]
9. S. Venkatesh, P. K. Yadav, D. C. Hasija, V. R. Patil, and M. M. V. Ramana, “Novel blue-light emitting fluorescent liquid crystals based on 4, 4′-(2-(tert-butyl)- anthracene-9, 10-diyl)diphenol and their optical behavior,” J. Mol. Liq. 310, 113265 (2020). [CrossRef]
10. T. Sakurai, M. Kobayashi, H. Yoshida, and M. Shimizu, “Remarkable increase of fluorescence quantum efficiency by cyano substitution on an ESIPT molecule 2-(2-hydroxyphenyl)benzothiazole: a highly photoluminescent liquid crystal dopant,” Crystals 11(9), 1105 (2021). [CrossRef]
11. S. Yang, B. Zhang, S. R. Murdock, and P. J. Collings, “Orientational order of dyes in a lyotropic chromonic liquid crystal,” Soft Matter 18(38), 7415–7421 (2022). [CrossRef]
12. X. Zhang, Y. Xu, C. Valenzuela, X. Zhang, L. Wang, W. Feng, and Q. Li, “Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence,” Light: Sci. Appl. 11(1), 223 (2022). [CrossRef]
13. H. Coles and S. Morris, “Liquid-crystal lasers,” Nat. Photonics 4(10), 676–685 (2010). [CrossRef]
14. J. Mysliwiec, A. Szukalska, A. Szukalski, and L. Sznitko, “Liquid crystal lasers: the last decade and the future,” Nanophotonics 10(9), 2309–2346 (2021). [CrossRef]
15. C. Mowatt, S. M. Morris, M. H. Song, T. D. Wilkinson, R. H. Friend, and H. J. Coles, “Comparison of the performance of photonic band-edge liquid crystal lasers using different dyes as the gain medium,” J. Appl. Phys. 107(4), 043101 (2010). [CrossRef]
16. M. Chapran, E. Angioni, N. J. Findlay, B. Breig, V. Cherpak, P. Stakhira, T. Tuttle, D. Volyniuk, J. V. Grazulevicius, Y. A. Nastishin, O. D. Lavrentovich, and P. J. Skabara, “An ambipolar BODIPY derivative for a white exciplex OLED and cholesteric liquid crystal laser toward multifunctional devices,” ACS Appl. Mater. Interfaces 9(5), 4750–4757 (2017). [CrossRef]
17. A. Adamow, L. Sznitko, E. Chrzumnicka, J. Stachera, A. Szukalski, T. Martynski, and J. Mysliwiec, “The ultra-photostable and electrically modulated stimulated emission in perylene-based dye doped liquid crystal,” Sci. Rep. 9(1), 2143 (2019). [CrossRef]
18. A. Adamow, A. Szukalski, L. Sznitko, L. Persano, D. Pisignano, A. Camposeo, and J. Mysliwiec, “Electrically controlled white laser emission through liquid crystal/polymer multiphases,” Light: Sci. Appl. 9(1), 19 (2020). [CrossRef]
19. Q. Yang, J.-C. Zhu, Z.-X. Li, X.-S. Chen, Y.-X. Jiang, Z.-W. Luo, P. Wang, and H.-L. Xie, “Luminescent liquid crystals based on carbonized polymer dots and their polarized luminescence application,” ACS Appl. Mater. Interfaces 13(22), 26522–26532 (2021). [CrossRef]
20. N. Wang, J. S. Evans, J. Mei, J. Zhang, I.-C. Khoo, and S. He, “Lasing properties of a cholesteric liquid crystal containing aggregation-induced-emission material,” Opt. Express 23(26), 33938 (2015). [CrossRef]
21. L.-X. Guo, Y.-B. Xing, M. Wang, Y. Sun, X.-Q. Zhang, B.-P. Lin, and H. Yang, “Luminescent liquid crystals bearing an aggregation-induced emission active tetraphenylthiophene fluorophore,” J. Mater. Chem. C 7(16), 4828–4837 (2019). [CrossRef]
22. J. Voskuhl and M. Giese, “Mesogens with aggregation-induced emission properties: Materials with a bright future,” Aggregate 3(1), e124 (2022). [CrossRef]
23. F. Würthner, T. E. Kaiser, and C. R. Saha-Möller, “J-aggregates: from serendipitous discovery to supramolecular engineering of functional dye materials,” Angew. Chem. Int. Ed. 50(15), 3376–3410 (2011). [CrossRef]
24. J. L. Bricks, Y. L. Slominskii, I. D. Panas, and A. P. Demchenko, “Fluorescent J-aggregates of cyanine dyes: basic research and applications review,” Methods Appl. Fluoresc. 6(1), 012001 (2017). [CrossRef]
25. J. Knoester and V. M. Agranovich, “Frenkel and Charge-Transfer Excitons in Organic Solids,” in Thin Films and Nanostructures: Electronic Excitations in Organic Based Nanostructures, Volume 31, V. M. Agranovich and G. F. Bassani, eds. (Elsevier, 2003), 31(03), pp. 1–96.
26. W. J. Harrison, D. L. Mateer, and G. J. T. Tiddy, “Liquid-crystalline J-aggregates formed by aqueous ionic cyanine dyes,” J. Phys. Chem. 100(6), 2310–2321 (1996). [CrossRef]
27. S. Herbst, B. Soberats, P. Leowanawat, M. Lehmann, and F. Würthner, “A Columnar liquid-crystal phase formed by hydrogen-bonded perylene bisimide J-aggregates,” Angew. Chem. Int. Ed. 56(8), 2162–2165 (2017). [CrossRef]
28. S. Herbst, B. Soberats, P. Leowanawat, M. Stolte, M. Lehmann, and F. Würthner, “Self-assembly of multi-stranded perylene dye J-aggregates in columnar liquid-crystalline phases,” Nat. Commun. 9(1), 2646 (2018). [CrossRef]
29. T. Ma, Z. Wang, C. Song, N. Song, J. Ren, B. Liu, H. Zhang, H. Zhang, and D. Lu, “J-Aggregate Behavior of Poly[(9,9- dioctyluorenyl-2,7-diyl)- alt -co-(bithiophene)] (F8T2) in crystal and liquid crystal phases,” J. Phys. Chem. C 123(39), 24321–24327 (2019). [CrossRef]
30. Y. Ma, A. Dicce, N. R. Reddy, and J. Fang, “Liquid-crystalline ordering of Davydov-split aggregates of cyanine dyes,” Colloids Surf., A 642, 128713 (2022). [CrossRef]
31. A. P. Demchenko, “Photobleaching of organic fluorophores: quantitative characterization, mechanisms, protection,” Methods Appl. Fluoresc. 8(2), 022001 (2020). [CrossRef]
32. D. O. Faulkner, J. J. McDowell, A. J. Price, D. D. Perovic, N. P. Kherani, and G. A. Ozin, “Measurement of absolute photoluminescence quantum yields using integrating spheres - Which way to go?” Laser Photon. Rev. 6(6), 802–806 (2012). [CrossRef]
33. T.-S. Ahn, R. O. Al-Kaysi, A. M. Müller, K. M. Wentz, and C. J. Bardeen, “Self-absorption correction for solid-state photoluminescence quantum yields obtained from integrating sphere measurements,” Rev. Sci. Instrum. 78(8), 086105 (2007). [CrossRef]
34. J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 3rd ed. (Springer US, 2006).
35. S. Makio, N. Kanamaru, and J. Tanaka, “The J-aggregate 5,5′,6,6′-Tetrachloro-1,1′-diethyl-3,3′-bis(4-sulfobutyl)benzimidazolocarbocyanine Sodium Salt in Aqueous Solution,” Bull. Chem. Soc. Jpn. 53(11), 3120–3124 (1980). [CrossRef]
36. A. Pawlik, A. Ouart, S. Kirstein, H.-W. Abraham, and S. Daehne, “Synthesis and UV/Vis spectra of J-aggregating 5,5′,6,6′-tetrachlorobenzimidacarbocyanine dyes for artificial light-harvesting systems and for asymmetrical generation of supramolecular helices,” Eur. J. Org. Chem. 2003(16), 3065–3080 (2003). [CrossRef]
37. M. van Burgel, D. A. Wiersma, and K. Duppen, “The dynamics of one-dimensional excitons in liquids,” J. Chem. Phys. 102(1), 20–33 (1995). [CrossRef]
38. J. Moll, S. Daehne, J. R. Durrant, and D. A. Wiersma, “Optical dynamics of excitons in J aggregates of a carbocyanine dye,” J. Chem. Phys. 102(16), 6362–6370 (1995). [CrossRef]
39. M. S. Bradley, J. R. Tischler, and V. Bulović, “Layer-by-layer J-aggregate thin films with a peak absorption constant of 106 cm–1,” Adv. Mater. 17(15), 1881–1886 (2005). [CrossRef]
40. A. V. Sorokin, I. Y. Ropakova, R. S. Grynyov, M. M. Vilkisky, V. M. Liakh, I. A. Borovoy, S. L. Yefimova, and Y. V. Malyukin, “Strong difference between optical properties and morphologies for J-Aggregates of similar cyanine dyes,” Dyes Pigm. 152, 49–53 (2018). [CrossRef]
41. A. V. Sorokin, I. Y. Ropakova, S. Wolter, R. Lange, I. Barke, S. Speller, S. L. Yefimova, Y. V. Malyukin, and S. Lochbrunner, “Exciton dynamics and self-trapping of carbocyanine j-aggregates in polymer films,” J. Phys. Chem. C 123(14), 9428–9444 (2019). [CrossRef]
42. P. V. Pisklova, I. Y. Ropakova, I. I. Bespalova, S. L. Yefimova, and A. V. Sorokin, “Interaction between molecular aggregates placed into thin layered films,” Mol. Cryst. Liq. Cryst. 753(1), 61–72 (2023). [CrossRef]
43. P. Pisklova, I. Ropakova, I. Bespalova, S. Kryvonogov, O. Viagin, S. Yefimova, and A. Sorokin, “Features of cyanine dyes aggregation on differently charged TiO2 matrices,” Chem. Phys. Impact 6, 100176 (2023). [CrossRef]
44. I. I. Grankina, I. A. Borovoy, S. I. Petrushenko, S. S. Hrankina, V. P. Semynozhenko, S. L. Yefimova, and A. V. Sorokin, “Fluorescent properties of amphi-PIC J-aggregates in the complexes with bovine serum albumin,” J. Mol. Liq. 368, 120755 (2022). [CrossRef]
45. H. Horiuchi, S. Ishida, K. Matsuzaki, K. Tani, T. Hashimoto, H. Hotta, K. Tsunoda, T. Kodaira, T. Okutsu, and H. Hiratsuka, “Suppression mechanism of the photodegradation of J-aggregate thin films of cyanine dyes by coating with polysilanes,” J. Phys. Chem. C 115(14), 6902–6909 (2011). [CrossRef]
46. Y. V. Malyukin, A. V. Sorokin, S. L. Yefimova, and A. N. Lebedenko, “Photo-induced reorganization of molecular packing of amphi-PIC J-aggregates (single J-aggregate spectroscopy),” J. Lumin. 112(1-4), 429–433 (2005). [CrossRef]
47. K. A. Clark, E. L. Krueger, and D. A. Vanden Bout, “Direct measurement of energy migration in supramolecular,” J. Phys. Chem. Lett. 5(13), 2274–2282 (2014). [CrossRef]
48. A. V. Sorokin, I. Y. Ropakova, S. L. Yefimova, and Y. V. Malyukin, “Influence of pseudoisocyanine J-aggregate agglomeration on the optical properties,” Funct.Mater. 25(1), 088–092 (2018). [CrossRef]
49. C. Rehhagen, M. Stolte, S. Herbst, M. Hecht, S. Lochbrunner, F. Würthner, and F. Fennel, “Exciton migration in multistranded perylene bisimide J-aggregates,” J. Phys. Chem. Lett. 11(16), 6612–6617 (2020). [CrossRef]
50. B. Wittmann, F. A. Wenzel, S. Wiesneth, A. T. Haedler, M. Drechsler, K. Kreger, J. Köhler, E. W. Meijer, H.-W. Schmidt, and R. Hildner, “Enhancing long-range energy transport in supramolecular architectures by tailoring coherence properties,” J. Am. Chem. Soc. 142(18), 8323–8330 (2020). [CrossRef]
51. S. B. Anantharaman, J. Kohlbrecher, G. Rainò, S. Yakunin, T. Stöferle, J. Patel, M. Kovalenko, R. F. Mahrt, F. A. Nüesch, and J. Heier, “Enhanced room-temperature photoluminescence quantum yield in morphology controlled J-aggregates,” Adv. Sci. 8(4), 1903080 (2021). [CrossRef]
52. X. Yang, Z. Dai, A. Miura, and N. Tamai, “Different back electron transfer from titanium dioxide nanoparticles to tetra (4-sulfonatophenyl) porphyrin monomer and its J-aggregate,” Chem. Phys. Lett. 334(4-6), 257–264 (2001). [CrossRef]
53. A. I. Goncharuk, N. I. Lebovka, L. N. Lisetski, and S. S. Minenko, “Aggregation, percolation and phase transitions in nematic liquid crystal EBBA doped with carbon nanotubes,” J. Phys. D: Appl. Phys. 42(16), 165411 (2009). [CrossRef]
54. LА Bulavin, L. N. Lisetski, S. S. Minenko, A. N. Samoilov, V. V. Klepko, S. I. Bohvan, and N. I. Lebovka, “Microstructure and optical properties of nematic and cholesteric liquid crystals doped with organo-modified platelets,” J. Mol. Liq. 267, 279–285 (2018). [CrossRef]
55. M. Schadt, “Liquid crystal materials and liquid crystal displays,” Annu. Rev. Mater. Sci. 27(1), 305–379 (1997). [CrossRef]
