Aggregation of Carbocyanine Dyes in Choline Chloride-Based Deep

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Aggregation of Carbocyanine Dyes in Choline Chloride Based Deep Eutectic Solvents in the Presence of Aqueous Base Mahi Pal, Anita Yadav, and Siddharth Pandey Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01981 • Publication Date (Web): 22 Aug 2017 Downloaded from http://pubs.acs.org on August 24, 2017

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Aggregation of Carbocyanine Dyes in Choline Chloride Based Deep Eutectic Solvents in the Presence of Aqueous Base

Mahi Pal, Anita Yadav and Siddharth Pandey*

Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi – 110016, India.

*

Corresponding Author. [email protected]. Phone: +91-11-26596503. Fax: +91-

11-26581102.

1 ACS Paragon Plus Environment

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ABSTRACT: Deep eutectic solvents (DESs) have shown potential as novel media to support molecular aggregation. Self-aggregation behavior of two common and popular carbocyanine

dyes,

5,5’,6,6’-tetrachloro-1,1’-diethyl-3,3’-di(4-sulfobutyl)-benzimidazole

carbocyanine (TDBC) and 5,5’-dichloro-3,3’-di(3-sulfopropyl)-9-methyl-benzothiacarbo cyanine (DMTC), is investigated within DES-based systems under ambient conditions. While TDBC is known to form J-aggregates in basic aqueous solution, DMTC forms H-aggregates under similar conditions. The DESs used, glyceline and reline, are composed of salt choline chloride and two vastly different H-bond donors, glycerol and urea, respectively, in 1 : 2 mole ratios. Both DESs in the presence of base are found to support J-aggregates of TDBC. These fluorescent J-aggregates are characterized by small Stokes’ shifts and sub-nanosecond fluorescence lifetimes. Under similar conditions, DMTC forms fluorescent H-aggregates along with J-aggregates within the two DES-based systems. Addition of cationic surfactant cetyltrimethylammonium bromide (CTAB) below its critical micelle concentration (cmc) to TDBC solution of aqueous base-added glyceline shows prominent presence of J-aggregates, increasing CTAB concentration above cmc results in disruption of J-aggregates and formation of unprecedented H-aggregates. DMTC exclusively forms H-aggregates within CTAB solution of aqueous base-added glyceline irrespective of the surfactant concentration. Anionic surfactant, sodium dodeylsulfate (SDS), present below its cmc within aqueous baseadded DESs supports J-aggregation by TDBC; for similar SDS addition, DMTC forms Haggregates within glyceline-based system whereas both H- and J-aggregates exist within reline-based system. Comparison of the carbocyanine dye behavior in various aqueous baseadded DES systems to that in aqueous basic media reveals contrasting aggregation tendency and/or efficiency. Surfactants as additives are demonstrated to control and modulate carbocyanine dye self-aggregation within DES-based media. The unique nature of DESs as alternate media toward affecting cyanine dye aggregation is highlighted.


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INTRODUCTION Deep eutectic solvents (DESs) have emerged as inexpensive environmentally-benign nonaqueous alternatives to both organic solvents and ionic liquids.1 The most common, popular, and cost-effective DESs are constituted of a halide salt (mostly belonging to ammonium- or phosphonium-family) and a prominent hydrogen bond (HB) donor.2 Among the halide salts, a quaternary ammonium halide salt, choline chloride (ChCl), has been used extensively to prepare DESs as it is inexpensive and non-toxic.3,4 A ChCl-based DES can be simply prepared by mixing a HB donor with ChCl in pre-determined molar ratio (usually obtained from the temperature-composition phase diagram) and gently heating to form a liquid at ambient conditions. The ChCl-based DESs have shown many applications in chemistry and chemical technology.5-10 As the H-bonding interaction between the halide salt and the HB donor is proposed to be the reason for the lowered freezing point and the liquid state of the DESs at ambient conditions, researchers have explored various avenues of molecular aggregation within DESs and DES-based systems.11-18 In this regard, DESs afford non-aqueous (water-free) H-bonded systems with potential for molecular aggregation. Consequently, several surfactants and amphiphiles have been demonstrated to self-assemble to form normal and reverse micelles, microemulsions, vesicles, and other aggregated species within such DESs.11-18 The carbocyanine dyes are known to self-associate in solutions due to the presence of strong intermolecular van der Waals-like forces of attraction.19 These dyes can aggregate to form the so-called J-aggregates, usually characterized by a very narrow, intense absorption band (J-band), which is bathochromically shifted from the monomer absorption band (Mband). The J-aggregates arise from the formation of a staircase-type head-to-tail arrangement (end-to-end stacking) of the dye molecules. In certain conditions, the carbocyanine dyes may form H-aggregates that arise from plane-to-plane stacking into a sandwich-type arrangement.


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The H-aggregates are usually characterized by a broader hypsochromically-shifted absorption band (H-band).20-22 Transition dipoles are aligned parallel in J-aggregates and perpendicular in H-aggregates to the line connecting neighboring molecules in the aggregate.23-27 J- and Haggregates can be distinguished on the basis of the angle between the line of centers of a column of dye molecules and the long axis of any one of the parallel molecules called slippage angle (α). While large molecular slippage (α < 32°) implies formation of Jaggregates, small slippage (α > 32°) results in H-aggregation.28 These aggregates are known to play an important role in many technological applications.29-36 The dye aggregates exhibit a strong coherent excitation phenomenon resulting in their ultrafast and high nonlinear optical responses.37-39 Their unique optical properties, such as fast electron transfer and long distance excitonic energy propagation, have led to their applications as optical switches, serial-toparallel pulse converters, and heterojunction photovoltaic devices.40 Importantly, dye aggregates are shown to be able to store light energy and release it essentially “on-demand”.40 The efficiencies of such energy and electron transfer processes are known to be sensitive to the specific aggregation state of the dye.41,42 The aggregation of carbocyanine dyes exhibits complex dependency not only on the dye structure and concentration, but also on the solubilizing milieu (solvent polarity, pH, ionic strength, temperature, H-bonding ability, etc.).29-42 As the high dielectric constant of water helps reduce the repulsive interactions between the charged carbocyanine dye molecules, dye molecules readily aggregate in water.43 High polarizability of π-electrons along the polymethine groups gives rise to strong dispersion forces between the carbocyanine molecules in solution.44 The dispersion forces between the polymethine chains serve as the main attractive forces for formation of extended aggregates of these type of dyes.45 Aggregation behavior of carbocyanine dyes has been investigated in ionic liquids recently.46-49 It is shown that the these carbocyanine dyes form fluorescent H-aggregates in


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ionic liquids containing BF4 anion and form J-aggregates in ionic liquids with other anions as 2 wt% 1 M aqueous NaOH was added to the ionic liquid solution of the dyes.46 This stark difference in carbocyanine dye aggregation was attributed to the hydrolytic properties of [BF4]– ionic liquids over other ionic liquids with [PF6]–, [(CF3SO2)2N]–, and [CF3SO3]– anions. As mentioned earlier, ChCl-based DESs are touted as non-toxic and inexpensive alternatives to ionic liquids, and they are recently shown to support various self-aggregation processes and sustain supramolecular assemblies (especially those of surfactants) due to the presence of extensive H-bonding interactions that give rise to substantial dipolarities.2,49 We envisaged that the structural features of the DESs may influence self-aggregation of these carbocyanine dyes in interesting manner and offer a novel non-aqueous media with interesting applications in the process. In this paper, we present self-association characteristics of two carbocyanine dyes within ChCl-based DESs under ambient conditions. While the first carbocyanine dye, 5,5’,6,6’-tetrachloro-1,1’-diethyl-3,3’-di(4-sulfobutyl)benzimidazolocarbocyanine

(TDBC),

is known to form J-aggregates in basic aqueous solution, the second dye, 5,5’-dichloro-3,3’di(3-sulfopropyl)-9-methyl-benzothiacarbocyanine (DMTC), readily forms H-aggregates under similar conditions. Outcomes of the investigation of the dye aggregation in surfactantadded DESs are also presented as amphiphiles in both monomeric and aggregated forms in aqueous media are known to significantly affect the dye aggregation process.

EXPERIMENTAL SECTION Materials. Cyanine dyes, TDBC and DMTC, were obtained from Hayashibara Biochemicals Laboratories, Inc., Japan in the highest purity and were used as received. DESs, reline 202/3 (MW 86.69 g.mol−1), a mixture of ChCl and urea (1 : 2 mole ratio) and glyceline 202 (MW 107.95 g.mol), a mixture of ChCl and glycerol (1 : 2 mole ratio) were purchased


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from Scionix Ltd. and used as received. The DESs were dried overnight under vacuum prior to their use. The water content of the dried DESs was cmc) in glyceline in the absence and presence of aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%) (recovered decay times and the criteria of the goodnessof-the-fit are presented in Table 1). The aggregation is characterized by a dominant (~99%) sub-nanosecond decay time and a ~2 ns decay time with minor contributions (~1%).

Behavior of DMTC. In water, presence of monomeric CTAB ([CTAB] = 0.1 mM) gives rise to DMTC H-aggregates with absorbance features (Fig. S5) similar to those observed for NaOH-added water (Fig. S2). This H-aggregate band shifts hypsochromically to maxima at 370 nm and loses its structure in the presence of 150 mM NaOH (Fig. S5). As mentioned earlier, these H-aggregates of DMTC are proposed to be structurally different


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from those with band maxima at 450 nm (vide supra). While within 1 mM CTAB (< cmc) solution of glyceline, DMTC only exists in monomeric form characterized by band centered around 550 nm, addition of aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%) results in nearly complete conversion of DMTC monomers into H-aggregated form after 5 min. of sample preparation (Fig. 7). While CTA+ monomers alone are not able to facilitate Haggregation of DMTC, addition of aqueous base results in highly efficient formation of Haggregates in glyceline. While the H-aggregates were also formed within base-added glyceline in the absence of CTAB, the solution also contained appreciable monomer and Jaggregates of DMTC (Fig. 3, vide supra). We believe CTA+ in the monomeric form not only facilitates H-aggregation by reducing the electrostatic repulsion between DMTC molecules, it also disrupts J-aggregate formation. The DMTC H-aggregates thus formed within aqueous-based added monomeric CTAB solution of glyceline are again found to be fluorescent, though weakly, in nature (Fig. 7, the H-aggregates are not fluorescent in monomeric CTAB solution in water, Fig. S5). Similar to that observed for DMTC in neat and aqueous-base added glyceline, the excitedstate intensity decay of DMTC dissolved in 1 mM CTAB (< cmc) solution of glyceline at 465 nm best fits to a double exponential decay function with a sub-ns decay time (0.7 ns) as the major contributor (~90%) and a longer (4.2 ns) decay time as the minor contributor (Fig. 8). In aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%)-added DMTC solution in glyceline, both the decay times decrease considerably (to 0.2 ns and 2.6 ns, respectively). The fluorescent H-aggregate formation has again resulted in decreased decay times of the carbocyanine dye. As the [CTAB] is increased above cmc in both water and glyceline, respectively, only the monomeric form of DMTC is found to exist in the solution; no J- or H- or D-band appears in the uv-vis absorbance spectra (Figs. S5 and 7). However, NaOH addition to micellar


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solution of glyceline (and of water) results in conversion of almost all DMTC monomers to H-aggregates. Thus, unlike in water, the DMTC aggregation behavior is similar in CTABadded glyceline irrespective of the CTAB concentration (Fig. 7); the dye readily forms Haggregates in the presence of base. This further implies that CTAB, in both micellar and monomeric forms, readily accommodate H-aggregates by decreasing the electrostatic repulsion between the carbocyanine dye molecules. The fluorescence emission spectra in the absence and presence of aqueous base within 25 mM CTAB (> cmc)-added glyceline solution of DMTC are also fairly similar to the one with 1 mM CTAB (< cmc) (Fig. 7). The excited-state intensity decay data is also similar where the two decay times [0.7 ns (major) and 4.0 ns (minor)] in the absence of aqueous base are decreased to 0.6 ns and 2.8 ns, respectively, in the presence of aqueous NaOH (Fig. 8 and Table 2).

Anionic Surfactant SDS-added Glyceline/Reline. Behavior of TDBC. SDS is one of the most popular of the anionic surfactants. Behavior of TDBC was first investigated in the presence of 5 mM SDS (< cmc) in water (Fig. S6). In contrast to the behavior in aqueous CTAB with [CTAB] < cmc, no J-band is observed even after 90 min. of sample preparation. Apparently, the anionic DS‒ fails to reduce charge repulsion between TDBC molecules perhaps due to electrostatic repulsion involving DS‒ and negatively charged part of TDBC. Addition of NaOH also does not appear to facilitate the aggregation process of the TDBC dye within aqueous solution containing monomeric anionic surfactant SDS. This is unusual as TDBC forms J-aggregates in neutral water, the Jaggregation efficiency is considerably increased in the presence of NaOH (Fig. S2). Therefore, it may be inferred that DS‒ effectively disrupts the J-aggregation process involving TDBC in water.


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As expected, within glyceline/reline with 1 mM SDS (< cmc), no J-band is observed (Fig. 9). However, as aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%) is added, the J-band readily evolves at the expense of the M-band in both glyceline and reline. It is noted that, under otherwise identical conditions, the ratio of the absorbance of the J- to M-band is much higher in aqueous NaOH-added glyceline with [SDS] < cmc than the corresponding reline solution (AJ/AM = 1.60 and 0.92, respectively). The higher efficiency of J-aggregation is due, in part, to the presence of glycerol in glyceline as opposed to urea in reline, where the presence of three –OH functionalities of glycerol in concert with DS‒ may be more conducive to J-aggregation as the aggregation process is usually favored in media with H-bonding interactions.2,49 More importantly, unlike in water, the DS‒ is not able to completely restrict the J-aggregation of TDBC in glyceline/reline though it decreases the efficiency of Jaggregate formation to some extent (compare Fig. 9 versus Fig. S6). The J-aggregation of TDBC dissolved in 1 mM SDS (< cmc) added glyceline/reline in the presence of aqueous NaOH is further corroborated by the fluorescence emission spectra of the carbocyanine dye (Fig. 9). The J-band readily appears at 597/591 nm (in glyceline/reline) as aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%) is added indicating the J-aggregates to be fluorescent in nature. The fact that the J-aggregation efficiency is more pronounced in aqueous NaOH-added glyceline as compared to aqueous NaOH-added reline with [SDS] < cmc is again emphasized by the steady-state fluorescence data. Excited-state intensity decay of TDBC dissolved in 1 mM SDS solution of glyceline/reline in the absence of base again fits best to a double exponential decay model with ~98% contribution from the decay time in the range 1.4-1.8 ns and the rest from the decay time in the range 19-22 ns (Fig. 10 and Table 1). However, as aqueous NaOH is added to the SDS solution of glyceline/reline, the 1.4-1.8 ns decay time decreased to subnanosecond again characterizing the J-aggregates in the media.


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The samples of TDBC dissolved in glyceline/reline with [SDS] > cmc in the absence and presence of aqueous NaOH partially solidified, and thus, no data acquisition was possible.

Behavior of DMTC. DMTC solutions in glyceline and reline, respectively, in the presence of 1 mM SDS (< cmc), do not support any aggregation as the uv-vis absorbance spectra show presence of only the M-band centered at 550 nm (Fig. 11). Addition of aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%) to 1 mM SDS solution in glyceline/reline results in significant changes in the uv-vis absorbance spectra of DMTC. In the corresponding glyceline solution, after equilibrium is achieved, the M-band is diminished and a weak shoulder representing J-aggregates at 610 nm appears. More importantly, band centered at 400 nm representing H-aggregates prominently shows up. The aggregation of DMTC in same amount of aqueous NaOH-added 1 mM SDS solution of reline is a little different (Fig. 11). The presence of both the J-band (centered at 610 nm) and the H-band (centered at 390 nm) is clearly seen along with the M-band (centered at 550 nm) as the shoulder. It is clear that the identity of the DES effectively controls the aggregation pattern of this carbocyanine dye in the presence of monomeric SDS. The H-aggregates thus formed in both 1 mM SDS-added glyceline and reline in the presence of aqueous NaOH (final [NaOH] = 1.7 M, water = 30 wt%) are also found to be highly fluorescent in nature with emission peak appearing at 465 nm (Fig. 11). In line with that observed earlier, these H-aggregates formed by DMTC in both glyceline/reline have significantly shorter lifetimes as compared to the un-aggregated DMTC (Fig. 12 and Table 2) as revealed by the excited-state emission intensity decay data collected at 465 nm. All-in-all, the role of HBD in DES (glycerol in glyceline versus urea in reline) in aggregation behavior of DMTC in the presence of SDS and base is amply highlighted.


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Conclusions In conclusion, we have found that the carbocyanine dyes TDBC and DMTC can selfaggregate into J- or H-aggregates within DES-based systems depending on the additives present. While neat DESs as such do not support any dye aggregation, addition of aqueous NaOH or CTAB/SDS solution of aqueous NaOH can readily trigger formation of dye aggregates. Though not too much difference in aggregation behavior is observed within two DESs with different H-bond donors, the dye aggregation tendency or efficiency within aqueous NaOH-added DES-based media is found to be different from that observed in corresponding aqueous basic media. CTAB and SDS, respectively, are demonstrated to effectively control and modulate TDMC/DMTC self-aggregation within DES-based media, affording new avenues of aggregate formation in some cases. The unique nature of DESs as alternate media toward supporting cyanine dye aggregation is amply highlighted. The results presented here support the growing potential of DESs in their applications in important molecular aggregation processes due to their inherent architecture and properties.

Supporting Information. Figures S1-S6. This material is available free of charge via the Internet at http://pubs.acs.org.

ACKNOWLEDGMENT: This work is generously supported by the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India, through a grant to Siddharth Pandey (EMR/2016/005053). Mahi Pal and Anita Yadav thank University Grants Commission (UGC) and Council of Scientific and Industrial Research (CSIR), Government of India, respectively, for their fellowships.


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Cl N Cl

N

N

Cl

N Cl Na

-

O3S

SO3TDBC

Scheme 1. Structures of Deep Eutectic Solvents and Carbocyanine Dyes used in this study.


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Table 1: Recovered intensity decay parameters for 10 µM TDBC dissolved in different DESbased systems (final [NaOH]) = 1.7 M and water = 30 wt%). Excitation was carried out using a 405 nm LED and emission was collected at 595 nm. Errors associated with decay times are ≤ 10%. ___________________________________________________________________________ τ2/ns f 1% f 2% χ2 System τ1/ns ___________________________________________________________________________ Neat Glyceline 1.78 100 4.17 1.25 16.9 98 2 1.10 Aqueous NaOH-added Glyceline

0.14 100 2.68 0.09 13.7 99.9 0.1 1.08 _________________________________________________________________________ Neat Reline 2.44 100 5.73 1.58 18.9 97 3 1.30 Aqueous NaOH-added Reline

0.59 100 4.67 0.38 13.7 99 1 1.28 __________________________________________________________________________ 1 mM CTAB (< cmc) in Glyceline 1.99 100 4.22 1.44 19.4 98 2 1.09 Aqueous NaOH-added 0.31 100 2.35 0.1 1.06 1 mM CTAB (< cmc) in Glyceline 0.27 15.7 99.9 __________________________________________________________________________ 25 mM CTAB (> cmc) in Glyceline 0.09 100 1.45 0.08 1.5 100 0 0.77 Aqueous NaOH-added 0.25 100 1.96 25 mM CTAB (> cmc) in Glyceline 0.18 2.0 99 1 1.02 __________________________________________________________________________ 1 mM SDS (< cmc) in Glyceline 2.17 100 4.93 1.50 19.3 98 2 1.18 Aqueous NaOH-added 0.18 100 1.46 1 mM SDS (< cmc) in Glyceline 0.16 9.4 100 0 1.03 __________________________________________________________________________ 1 mM SDS (< cmc) in Reline 2.69 100 6.10 1.77 20.2 97 3 1.31 Aqueous NaOH-added 0.99 100 5.40 1 mM SDS (< cmc) in Reline 0.60 15.6 99 1 1.29 ___________________________________________________________________________


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Table 2: Recovered intensity decay parameters for 10 µM DMTC dissolved in different DESbased systems (final [NaOH]) = 1.7 M and water = 30 wt%). Excitation was carried out using a 405 nm LED and emission was collected at 465 nm. Errors associated with decay times are ≤ 10%. ___________________________________________________________________________ τ2/ns f 1% f 2% χ2 System τ1/ns ___________________________________________________________________________ Neat Glyceline 1.51 100 5.28 0.42 3.7 91 9 1.00 Aqueous NaOH-added Glyceline

0.45 100 7.51 0.13 1.7 98 2 1.02 ___________________________________________________________________________ Neat Reline 1.51 100 4.11 0.94 5.2 93 7 0.99 Aqueous NaOH-added Reline

0.98 100 1.59 0.48 1.4 76 24 1.00 __________________________________________________________________________ 1 mM CTAB (< cmc) in Glyceline 1.61 100 6.48 0.71 4.2 90 10 1.03 Aqueous NaOH-added 0.46 100 3.96 1 mM CTAB (< cmc) in Glyceline 0.22 2.6 97 3 1.05 ___________________________________________________________________________ 25 mM CTAB (> cmc) in Glyceline 1.03 100 3.42 0.73 4.0 96 4 1.07 Aqueous NaOH-added 0.86 100 3.01 25 mM CTAB (> cmc) in Glyceline 0.59 2.8 95 5 1.05 __________________________________________________________________________ 1 mM SDS (< cmc) in Glyceline 2.74 100 5.26 0.12 2.5 99 1 1.02 Aqueous NaOH-added 0.36 100 6.48 1 mM SDS (< cmc) in Glyceline 0.11 1.6 98 2 1.03 __________________________________________________________________________ 1 mM SDS (< cmc) in Reline 0.16 100 1.23 0.81 2.1 99.9 0.1 1.04 Aqueous NaOH-added 1.06 100 1.23 1 mM SDS (< cmc) in Reline 0.03 1.1 99.9 0.1 1.04 ___________________________________________________________________________


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Figure Captions Figure 1.

Absorbance (50 µM) and fluorescence emission (10 µM, λex = 430 nm) spectra of TDBC dissolved in neat glyceline/reline (green) and 90 minutes after the addition of aqueous NaOH to glyceline/reline (blue, [NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 2.

Fits to single-exponential (left) and double-exponential (right) decay functions of the excited-state intensity decay at 595 nm (λex = 405 nm) of 10 µM TDBC dissolved in neat glyceline/reline and 90 minutes after the addition of aqueous NaOH to glyceline/reline ([NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 3.

Absorbance (50 µM) and fluorescence emission (10 µM, λex = 430 nm) spectra of DMTC dissolved in neat glyceline/reline (green) and 90 minutes after the addition of aqueous NaOH to glyceline/reline (blue, [NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 4.

Fits to single-exponential (left) and double-exponential (right) decay function of the excited-state intensity decay at 465 nm (λex = 405 nm) of 10 µM DMTC dissolved in neat glyceline/reline and 90 minutes after the addition of aqueous NaOH to glyceline/reline ([NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 5.

Absorbance (50 µM) and fluorescence emission (10 µM, λex = 430 nm) spectra of TDBC dissolved in CTAB-added glyceline (green, [CTAB] = 1 mM < cmc, 25 mM > cmc) and 90 minutes after the addition of aqueous NaOH to CTAB-added glyceline (blue, [NaOH] = 1.7 M, 30 wt% water) under ambient conditions.


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Figure 6.

Fits to single-exponential (left) and double-exponential (right) decay function of the excited-state intensity decay at 595 nm (λex = 405 nm) of 10 µM TDBC dissolved in CTAB-added glyceline ([CTAB] = 1 mM < cmc, 25 mM > cmc), and 90 minutes after the addition of aqueous NaOH to CTAB-added glyceline ([NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 7.

Absorbance (50 µM) and fluorescence emission (10 µM, λex = 430 nm) spectra of DMTC dissolved in CTAB-added glyceline (green, [CTAB] = 1 mM < cmc, 25 mM > cmc) and 90 minutes after the addition of aqueous NaOH to CTAB-added glyceline (blue, [NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 8.

Fits to single-exponential (left) and double-exponential (right) decay function of the excited-state intensity decay at 465 nm (λex = 405 nm) of 10 µM DMTC dissolved in CTAB-added glyceline ([CTAB] = 1 mM < cmc, 25 mM > cmc), and 90 minutes after the addition of aqueous NaOH to CTAB-added glyceline ([NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 9.

Absorbance (50 µM) and fluorescence emission (10 µM, λex = 430 nm) spectra of TDBC dissolved in SDS-added glyceline/reline (green, [SDS] = 1 mM < cmc) and 90 minutes after the addition of aqueous NaOH to SDS-added glyceline/reline (blue, [NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 10.

Fits to single-exponential (left) and double-exponential (right) decay function of the excited-state intensity decay at 595 nm (λex = 405 nm) of 10 µM TDBC dissolved in SDS-added glyceline/reline ([SDS] = 1 mM < cmc) and 90 minutes after the addition of aqueous NaOH to SDS-added glyceline/reline ([NaOH] = 1.7 M, 30 wt% water) under ambient conditions.


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Figure 11.

Absorbance (50 µM) and fluorescence emission (10 µM, λex = 430 nm) spectra of DMTC dissolved in SDS-added glyceline/reline (green, [SDS] = 1 mM < cmc) and 90 minutes after the addition of aqueous NaOH to SDS-added glyceline/reline (blue, [NaOH] = 1.7 M, 30 wt% water) under ambient conditions.

Figure 12.

Fits to single-exponential (left) and double-exponential (right) decay function of the excited-state intensity decay at 465 nm (λex = 405 nm) of 10 µM DMTC dissolved in SDS-added glyceline/reline ([SDS] = 1 mM < cmc), and 90 minutes after the addition of aqueous NaOH to SDS-added glyceline/reline ([NaOH] = 1.7 M, 30 wt% water) under ambient conditions.


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Figure 1:


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Figure 2:


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Figure 3:


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Figure 4:


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Figure 5:


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Figure 6:


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Figure 7:


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Figure 8: 40 ACS Paragon Plus Environment

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Figure 9:


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Figure 10: 42 ACS Paragon Plus Environment

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Figure 11:


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Figure 12:


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TOC 30 wt% Aqueous NaOH

TDBC

+

+

30 wt% Water

TDBC/DMTC

DMTC DESs Water

J-aggregate H-aggregate Aq. NaOH

Monomers


Aggregation of Carbocyanine Dyes in Choline Chloride-Based Deep

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