Ingredients to TICT Formation in Donor Substituted Hemithioindigo

Letter pubs.acs.org/JPCL

Ingredients to TICT Formation in Donor Substituted Hemithioindigo Sandra Wiedbrauk,† Benjamin Maerz,‡ Elena Samoylova,‡ Peter Mayer,† Wolfgang Zinth,‡ and Henry Dube*,† †

Department für Chemie and Munich Center for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, D-81377 Munich, Germany ‡ Institut für BioMolekulare Optik, Fakultät für Physik and Munich Center for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, D-80538 Munich, Germany S Supporting Information *

ABSTRACT: Twisted intramolecular charge transfer (TICT) formation in hemithioindigo photoswitches has recently been reported and constitutes a second deexcitation pathway complementary to photoisomerization. Typically, this behavior is not found for this type of photoswitches, and it takes special geometric and electronic conditions to realize it. Here we present a systematic study that identifies the molecular preconditions leading to TICT formation in donor substituted hemithioindigo, which can thus serve as a frame of reference for other photoswitching systems. By varying the substitution pattern and providing an in-depth physical characterization including time-resolved and quantum yield measurements, we found that neither ground-state pretwisting along the rotatable single bond nor the introduction of strong push−pull character across the photoisomerizable double bond alone leads to formation of TICT states. Only the combination of both ingredients produces light-induced TICT behavior in polar solvents.

H

in polar solvents27 and serve as positive controls in this study. They possess both severe twisting of the stilbene fragment and a strong donor substituent in conjugation with the photoisomerizable double bond. HTIs Z-3 and Z-4 bear the same strong donor substituents but are planar in their ground state. HTIs Z-5 and Z-6 lack a strong donating substituent but are severely twisted around the rotatable single bond, whereas HTIs Z-7 and Z-8 bear substituents of moderate donating capacity and are also twisted. In all cases, the thioindigo fragment with its strongly electron-withdrawing carbonyl group serves as an intrinsic acceptor or pull-substituent of the photoisomerizable double bond. In comparison, the sulfur atom is a much weaker donating substituent with less effect on the electronics. By varying the donating capacity of the stilbene fragment, the push−pull character across the central double bond is therefore also varied simultaneously in the presented series. The synthesis of HTIs 1−8 follows established protocols and is described in full detail in the Supporting Information. The conformation of each HTI was analyzed in the solid state for derivatives Z-1 to Z-8 (Figure 1b) and in solution for all derivatives using a previously established NMR shift analysis.27 Indicative of a twisted stilbene fragment in solution is the chemical shift difference of the proton a signal (i.e., the proton in the ortho-position to the sulfur atom at the thioindigo fragment) observed upon Z to E isomerization. In the Z

emithioindigo (HTI) dyes are a class of emerging photoswitches1 that combine a variety of advantageous properties such as visible light responsiveness, high thermal bistability, and fatigue-resistant switching.2−7 Having been largely overlooked by the scientific community, HTIs have attracted recent attention as valuable alternative photoswitches with beneficial applicability in biological chemistry,8−11 supramolecular chemistry,12−15 or the field of molecular machines.16 Recently, we have found that certain pretwisted HTI derivatives undergo efficient formation of twisted intramolecular charge transfer (TICT)17−26 in polar solvents, which provides a second deexcitation channel via rotation around the single instead of the double bond.27 Depending on the nature of the solvent, different types of movement are therefore induced in these molecules by photoirradiation, which greatly expands the levels of control over molecular motions. Such refined control is of high interest for establishing more complex behavior of light-triggered molecules and for the design of emerging functions.28−35 A fundamental understanding of TICT formation in HTIs is now needed to allow rational implementation of these two-dimensional switching properties into future responsive systems. In this work, we present a comprehensive survey of the geometrical and electronic preconditions for TICT formation in HTI photoswitches. To this end, we compared a series of HTI derivatives 1−8 with different substitutions at the stilbene fragment of the molecule and different twisting angles36 around the rotatable single bond connecting the stilbene fragment with the photoisomerizable double bond (Figure 1). HTIs Z-1 and Z-2 show pronounced TICT formation upon photoirradiation © XXXX American Chemical Society

Received: February 15, 2017 Accepted: March 17, 2017 Published: March 17, 2017 1585

DOI: 10.1021/acs.jpclett.7b00371 J. Phys. Chem. Lett. 2017, 8, 1585−1592

Letter

The Journal of Physical Chemistry Letters

Figure 1. HTI derivatives 1−8 investigated for possible TICT formation in polar solvents. (a) Molecular structures. (b) Crystal structures of HTIs Z-1 to Z-8. Proton a, whose chemical NMR shift is indicative of the degree of twisting in solution, is indicated.

manifested by a strongly red-shifted fluorescence when the polarity of the solvent is increased. Frequently, dual fluorescence is also observed in polar solvents. The red-shifted part of the dual fluorescence allows for a first direct characterization of the TICT state if it can unambiguously be attributed to this state. In Figure 2, normalized stationary absorption and fluorescence spectra are presented for selected HTIs in different solvents. The corresponding spectra of the remaining derivatives are shown in the Supporting Information. Typical TICT behavior is seen for HTIs Z-1 and Z-2, displaying strong bathochromic shifts of their stationary fluorescence in polar solvents and dual fluorescence in solvents of very high polarity. The influence of solvent polarity on the absorption is comparatively small. Absorption and fluorescence spectra for Z-2 are shown in Figure 2a exemplarily. The corresponding planar derivatives Z-3 and Z-4 also exhibit solvatochromism of their absorption and fluorescence energies, but to a considerably weaker extent compared to that of Z-1 and Z-2 (see Figure 2b for Z-3). Even fewer bathochromic shifts are observed in polar solvents for the absorption and fluorescence of strongly twisted HTIs Z-5 and Z-6 carrying only weakly donating substituents (see Figure 2c for Z-5). HTIs Z-7 and Z-8 are both twisted to different degrees and at

configuration, proton a experiences either a strong downfield shift if the stilbene fragment is planar or an upfield shift if the stilbene fragment is severely twisted. If only a slight twist is present, the apparent shift difference is close to zero. The conformational preferences found in the crystals were also consistently observed in solution for a variety of solvents with different polarity. Only the behavior of Z-8 shows some deviations. While only a slight twisting is seen in the crystal (a torsion angle of 15° around the single bond), the twisting is apparently more severe in solution (see the Supporting Information for the detailed NMR analysis). We attribute this change in geometry to crystal packing effects and the presence of a possibly favorable O−S interaction37−43 between the methoxy-group oxygen atom and the sulfur atom of the thioindigo fragment in the solid state. The latter assumption is supported by the very short distance of 2.68 Å between the oxygen and the sulfur atom, which is far shorter than the sum of both van der Waals radii (3.32 Å). A first simple tool for the recognition of TICT formation is provided by analysis of the stationary fluorescence solvatochromism, with special emphasis on the influence of solvent polarity on Stokes shifts and occurrence of dual fluorescence. As TICT states are highly polar, their presence is typically 1586


Letter


Figure 2. Stationary normalized absorption (solid lines) and fluorescence (broken lines) spectra of HTIs (a) Z-2, (b) Z-4, (c) Z-5, and (d) Z-8 measured in cyclohexane (black), CH2Cl2 (green), and DMSO (red).

Table 1. Kinetic Data of Deexcitation and Quantum Yields of the Z/E Photoisomerization (ϕZ/E) and Fluorescence (ϕfl) for HTIs Z-1 to Z-8 HTI

solvent

polarity ET(30) /kcal mol−1

Z-1

cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO cyclohexane CH2Cl2 DMSO

30.9 40.7 45.1 30.9 40.7 45.1 30.9 40.7 45.1 30.9 40.7 45.1 30.9 40.7 45.1 30.9 40.7 45.1 30.9 40.7 45.1 30.9 40.7 45.1

Z-2

Z-3

Z-4

Z-5

Z-6

Z-7

Z-8

ϕZ/E /% 56 15 1.8 44 0.3 0.2 32 20 14 50 16 7 43 30 38 39 21 38 43 42 35 10 9 10

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

12 3 0.4 9 0.1 0.1 7 5 3 10 3 1 9 6 8 8 4 8 9 8 7 2 2 2

ϕfl /% 2 3 2 2 2 9 1 2 7 1 5

× × × × × × × × × × ×

7 1 4 6 1 3 6 8 2 4 2 4

× × × × × × × × × × × ×

10−2 ± 3 × 10−3 10−1 ± 4 × 10−2 10−2 ± 3 × 10−3 10−1 ± 3 × 10−2 10−2 ± 3 × 10−3 10−3 ± 1 × 10−3 10−1 ± 2 × 10−2 10−1 ± 3 × 10−2 10−1 ± 1 × 10−1 10−1 ± 1 × 10−2 10−1 ± 7 × 10−2 1 ± 2 × 10−1 −3 10 ± 1 × 10−3 10−2 ± 2 × 10−3 10−2 ± 5 × 10−3 10−3 ± 1 × 10−3 10−2 ± 2 × 10−3 10−2 ± 5 × 10−3 10−3 ± 1 × 10−3 10−3 ± 1 × 10−3 10−2 ± 2 × 10−3 10−1 ± 6 × 10−2 10−1 ± 3 × 10−2 10−1 ± 6 × 10−2

τSE /ps

τZ/E /ps

τT /ps

1.8 0.8 0.6 17 0.4 − 4.8 10 41 12 29 63 4.0 5.7

1.8 0.8 0.6 17 0.4 − 4.8 10 41 12 29 63 4.0 5.7

− 207 13 − 26 7.0 − − − − − − − −

4.3

4.3

−

28

28

− −

are more polar in nature compared to the Franck−Condon (FC) region. Determination of the photoisomerization quantum yield ϕZ/E and its dependence on solvent polarity provides another strong tool for TICT identification. Because TICT states are highly polar and represent an alternative and independent deexcitation channel, ϕZ/E is usually strongly diminished in more polar

the same time possess substituents of medium donating capacity. Neither shows a very strong response of its absorption or fluorescence to solvent polarity (see Figure 2d for Z-8). For all HTIs, fluorescence energies are more sensitive to solvent polarity changes than the absorption energies, demonstrating that the excited-state minima from which fluorescence occurs 1587


Letter


Figure 3. Time-resolved absorption spectra of HTIs (a) Z-2, (b) Z-4, (c) Z-5, and (d) Z-8 measured in CH2Cl2 at 22 °C. ESAs are shown in yellow−red, and SEs and GSBs are in blue.

solvents if TICT states are formed. In Table 1, the quantum yields ϕZ/E are given for all HTIs in solvents of different polarity, ranging from apolar cyclohexane to very polar DMSO. HTIs Z-1 and Z-2 show exactly the behavior described above: very efficient photoisomerization in apolar cyclohexane where no TICT formation is possible and a very strong decrease of ϕZ/E with increasing solvent polarity. In DMSO, ϕZ/E is close to zero for HTI Z-2. For HTIs Z-3 and Z-4, ϕZ/E also decreases strongly with increasing polarity of the solvent but does not reach the extremely low values observed for Z-1 and Z-2 in most polar DMSO. The ϕZ/E values of HTIs Z-5 to Z-8 are relatively independent of solvent polarity and remain comparatively high (in the range of 40% except for those for Z-8). The quantum yield of fluorescence ϕfl (see Table 1) is consistently found to be very low for all HTIs Z-1 to Z-8 regardless of the solvent. Time-resolved absorption spectroscopy provides a convenient tool to capture and characterize quickly decaying excited states and has helped to elucidate HTI photoisomerization mechanisms4−7,10,44,45 and TICT formation27 directly. A TICT state in HTIs is characterized by red-shifted excited-state absorptions (ESAs) and stimulated emissions (SEs), which decay significantly slower than the initially populated excitedstate minimum S1Min. In addition, increasing solvent polarity leads to considerably shorter lifetimes of the TICT states. These spectral earmarks are clearly seen for HTIs Z-1 and Z-2 in solvents more polar than cyclohexane.27 In Figure 3, the transient spectra of photoexcited HTIs Z-2, Z-4, Z-5, and Z-8 in CH2Cl2 are shown as examples with the absorption changes plotted against the probing wavelength and delay time. The reaction dynamics were analyzed by a rate equation model and fitted with exponential functions to obtain decay times for the different states involved and spectra of the corresponding fit amplitudes. Several time constants for the excited-state dynamics were found, the most important of which are discussed in the following. Directly after photoexcitation, very fast processes happen on the subpicosecond time scale associated with vibrational relaxation from the FC region to

the S1Min state. Subsequent relaxation from the S1Min state is designated with the time constant τSE as it is associated with easily recognizable SE. As Z to E isomerization directly proceeds from the S1Min state, the associated time constant τZ/E is identical to τSE. The lifetime of the TICT state is designated with τT. In CH2Cl2, the transient spectra of Z-2 (Figure 3a) clearly show occurrence of a second intermediate state, that is, the TICT state, with red-shifted SE and ESA features and significantly slower decay rates compared to the ones of the S1Min state. When the solvent polarity is increased, the spectral characteristics remain similar, but the decay times of the TICT state become significantly shorter. In apolar cyclohexane, no TICT state is seen in the time-resolved data but only population and decay of the S1Min state. For HTI Z-1, the very same behavior is observed: no TICT formation in cyclohexane, TICT formation and very long lifetimes of this state in medium polar solvents, and very efficient TICT formation having significantly shorter lifetimes in very polar solvents.27 To test if other HTIs in the here-presented series also form TICT states in polar solvents, we chose to investigate their time-resolved absorption after photoexcitation in CH2Cl2 as an exemplary solvent of intermediate polarity. In this solvent, TICT states should be visible for a conveniently long time before their decay, and therefore, they should be easily recognized. In the following, the time-resolved spectral characteristics of HTIs Z-4, Z-5, and Z-8 are discussed exemplarily for planar and strong donor substituted HTIs (Z-4), highly twisted HTIs without strong donors (Z-5), and twisted HTIs with medium strong donors (Z-8). The time-resolved data of HTIs Z-1 to Z3 in different solvents are published elsewhere,27 and those of HTI Z-4 in cyclohexane and DMSO, of Z-5 in cyclohexane, as well as of Z-6 in CH2Cl2 are given in the Supporting Information. For HTI Z-4 in CH2Cl2 (see Figure 3b), initial fast changes of the absorption take place and are associated with fast nuclear relaxations to reach the S1Min from the FC point. From the S1Min, a pronounced SE is visible with a lifetime 1588


Letter

The Journal of Physical Chemistry Letters of τSE = 29 ps. Upon decay of the SE, formation of the E isomer is seen by absorption changes at around 550 nm at late delay times. This behavior mirrors the well-established photoisomerization behavior of planar HTIs.4−7 No indication for the presence of a TICT state is seen for Z-4 in CH2Cl2. Additional time-resolved measurements in cyclohexane and DMSO also did not show TICT formation for this derivative. Instead, the common trend for planar HTIs is seen where the excited-state lifetime increases with increasing solvent polarity. For HTI Z-5 in CH2Cl2 (see Figure 3c), only very small spectral changes during the first ps are observed. This means that the S1Min state is not strongly stabilized against the FC region. According to the stationary fluorescence spectra of Z-5, which display only weakly solvent dependent Stokes shifts, no substantial excited-state relaxations to a possible TICT minimum should be observed. This is indeed the case; the ESA possesses dips at 400 and 490 nm associated with groundstate bleach (GSB) and SE from the S1Min state. Without further spectral shifts, the excited state decays with a lifetime of τZ/E = 5.7 ps and a signal characteristic of Z to E isomerization appears. The data of Z-8 in CH2Cl2 (see Figure 3d) display a GSB at 460 nm and ESA at 520 nm immediately after photoexcitation. Within the first ps, a SE at around 600 nm appears. Its signal is hidden under the strong ESA at early delay times. This is assigned to a stabilization of S1Min. The excited state decays with a lifetime of τZ/E = 28 ps, and a specific isomerization signal persists. In summary, TICT state formation and decay are clearly seen for Z-1 and Z-2, but no indications for a TICT state are observed in the time-resolved data of Z-3, Z-4, Z-5, Z-6, and Z-8. To unambiguously identify TICT state formation of HTI photoswitches, a variety of experimental evidence needs to be taken into cumulative consideration. Mechanistically, TICT formation represents an alternative excited-state pathway, which does not intermix with photoisomerization around the double bond but rather competes with it, leading to nonreactive deexcitation (Figure 4a). This is clearly seen for HTIs Z-1 and Z-2 by the shutdown of photoisomerization in very polar solvents while at the same time TICT states are efficiently formed. The contrary is observed in apolar cyclohexane: no TICT formation takes place but instead very efficient photoisomerization with very high ϕZ/E. Such behavior is usually explained by the highly polar nature of TICT states stemming from their considerable innate charge separation, which is in turn strongly stabilized by polar solvents. Apolar solvents do not stabilize TICT states accordingly and can therefore lead to suppression of their formation and to the preference of different excited-state pathways. If the solvent becomes more polar, TICT states become energetically accessible and are populated. If the polarity of the solvent is increased very strongly, stabilization of TICT states becomes so severe that they are (i) populated almost exclusively and (ii) are energetically close enough to the ground state for direct deexcitation, which decreases their lifetimes significantly. The hitherto identified TICT coordinate in HTIs is the single bond connecting the stilbene fragment to the photoisomerizable double bond. This assignment is most easily made for HTI Z-2 possessing only one rotatable single bond but could also be extended to Z-1 because of its very similar behavior with regard to all quantified properties. In the TICT state, the stilbene fragment is rotated by 90° out of conjugation with the double bond and can stably accumulate positive charge while negative charge builds up at the thioindigo fragment. This

Figure 4. TICT formation in HTI photoswitches. (a) General mechanism for TICT formation in HTI photoswitches with HTI Z-2 in CH2Cl2 as an example. In medium polar solvents, both TICT formation and double bond photoisomerization take place as mutually exclusive pathways starting from the S1Min state. The lifetime of the TICT state is considerably longer than the lifetime of the S1Min state, which increases its relative fluorescence intensity. (b) The essential ingredients necessary to induce TICT behavior in HTIs are strong ground-state twisting of the stilbene fragment and introduction of strong electron-donating substituents.

charge separation (and therefore TICT formation) should work the better with greater donor character of the stilbene fragment. However, strong donors are not always a guarantee for TICT formation, and there are also reported cases of TICT states in molecules having neither donor nor acceptor substitution.46,47 In the series of HTIs Z-1 to Z-8 investigated here, structural and electronic alterations were made to decipher the preconditions of TICT formation in HTI photoswitches. To unambiguously establish the presence of a TICT state in the photoreaction of HTI, the following characteristics had to be observed: (1) a strongly red-shifted and long-lived transient absorption and emission present in the time-resolved absorption spectra in polar CH2Cl2 in addition to the wellknown ESA features of the S1Min state and (2) a very strong decrease of ϕZ/E with increasing solvent polarity. Somewhat softer criteria include the following: (3) a strongly increasing Stokes shift with increasing solvent polarity, (4) possible occurrence of dual fluorescence in highly polar solvents, (5) a very low ϕfl because a direct optical transition of TICT states to the ground state is a forbidden process caused by their orthogonal π-systems, and (6) a severe decrease of the TICT state lifetime in the most polar solvents. All of the above criteria are fulfilled for HTIs Z-1 and Z-2, providing very good experimental evidence for the occurrence of a TICT state in polar solvents. For all other HTIs of this series, no such cumulative evidence for TICT formation was found experimentally. Rather, HTIs Z-3 to Z-8 behave very similar to unsubstituted HTI6 in their deexcitation character1589



■

istics, which are dominated by the double bond rotation pathway. This result gives unexpected and valuable insights into TICT formation in HTI photoswitches by showing that the structural and electronic prerequisites are very specific. Unlike many other known TICT-forming molecules, the presence of a strong donor group in an overall planar structure21,22,48 alone is not sufficient to induce TICT formation. Both planar Z-3 and Z-4 possess strong donor groups (NMe2 for Z-3 and julolidine for Z-4) but behave similar to planar HTIs bearing substituents of weaker donating character.5,7 Although some aspects of their behavior resemble that of TICT forming HTIs (such as the strong decrease of ϕZ/E with increasing polarity of the solvent for Z-4), the complete experimental evaluation firmly excludes TICT formation. Rotation around the double bond is still the dominant pathway for these planar derivatives. In HTIs Z-5 and Z-6, only weakly donating substituents are introduced into the stilbene fragment, but they are severely twisted along the prospective TICT coordinate in the ground state already. Despite this, TICT formation is not observed for these derivatives, and their overall behavior is again very similar to planar HTIs with photoisomerization as an efficient deexcitation pathway. HTIs Z-7 and Z-8 possess both a pretwisted stilbene fragment and substituents with significant donating capacity. Despite these properties, again no TICT formation occurs in the excited state, and the deexcitation behavior is characterized by double bond rotation regardless of the solvent used. Even three methoxy groups in resonance with the double bond apparently do not induce enough charge separation in the excited state to allow a stable TICT state to be formed in photoexcited Z-8. Thus, it requires both ingredients have considerable pretwisting of the stilbene fragment as well as a very strong donor group to induce TICT state formation in HTI photoswitches (Figure 4b). Neither pretwisting nor strong donor substituents alone are sufficient for this complex property to occur. Rather than the expected smooth transition of planar intramolecular charge transfer (PICT) to TICT behavior,20,24 we observe a very sharp onset of TICT formation if all structural and electronic parameters are tuned right. In this work, we have identified structural and electronic preconditions for TICT formation in HTI photoswitches. To this end, we have shown that the combination of different analytical techniques allows for clear judgment of the deexcitation mechanism and devised guideline criteria to identify TICT formation that can be transferred to other photoswitches. It appears that these preconditions are very specific and only a narrow set of properties allows establishing TICT behavior in this chromophore. Neither pretwisting of the stilbene fragment nor the presence of strong donor groups in planar HTIs alone leads to TICT formation. Both elements have to be present: a significant twist around the single bond connecting the stilbene fragment with the photoisomerizable double bond and a strong electron-donating group (e.g., NMe2) in resonance with the double bond. These findings now allow conscious implementation of TICT behavior in HTI photoswitches to obtain new complex and responsive molecular tools that can perform different visible light-triggered motions depending on the surrounding solvent. We are currently exploring the potential of TICT behavior in the context of molecular machines and responsive supramolecular systems.

Letter

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.7b00371. Crystal structural data (CIF) Detailed synthesis of HTIs Z-1 to Z-8 and full characterization, determination of physical properties including extinction coefficients, fluorescence and photoisomerization quantum yields, isomeric ratios obtained in the photostationary state at different wavelengths, thermal stability of HTIs E-1 to E-8, time-resolved absorption measurements of HTIs Z-4 to Z-6 in different solvents, conformational analysis in solution, stationary absorption and fluorescence in different solvents, and 1H and 13C NMR spectra (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Sandra Wiedbrauk: 0000-0002-5797-4522 Benjamin Maerz: 0000-0001-9242-1918 Elena Samoylova: 0000-0002-8186-3638 Peter Mayer: 0000-0002-1847-8032 Wolfgang Zinth: 0000-0003-3695-9486 Henry Dube: 0000-0002-5055-9924 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS H.D. thanks the “Fonds der Chemischen Industrie” for a Liebig fellowship and the Deutsche Forschungsgemeinschaft (DFG) for an Emmy-Noether fellowship. We further thank the Deutsche Forschungsgemeinschaft (SFB 749, A5 and A12) and the Clusters of Excellence “Munich-Center for Advanced Photonics” and “Center for Integrated Protein Science Munich” (CIPSM) for financial support.

■

REFERENCES

(1) Wiedbrauk, S.; Dube, H. Hemithioindigoan emerging photoswitch. Tetrahedron Lett. 2015, 56, 4266−4274. (2) Ichimura, K.; Seki, T.; Tamaki, T.; Yamaguchi, T. Fatigueresistant Photochromic Hemithioindigos. Chem. Lett. 1990, 19, 1645− 1646. (3) Yamaguchi, T.; Seki, T.; Tamaki, T.; Ichimura, K. Photochromism of Hemithioindigo Derivatives. I. Preparation and Photochromic Properties in Organic Solvents. Bull. Chem. Soc. Jpn. 1992, 65, 649−656. (4) Cordes, T.; Schadendorf, T.; Rück-Braun, K.; Zinth, W. Chemical control of Hemithioindigo-photoisomerization − Substituent-effects on different molecular parts. Chem. Phys. Lett. 2008, 455, 197−201. (5) Cordes, T.; Schadendorf, T.; Priewisch, B.; Rück-Braun, K.; Zinth, W. The Hammett Relationship and Reactions in the Excited Electronic State: Hemithioindigo Z/E-Photoisomerization. J. Phys. Chem. A 2008, 112, 581−588. (6) Nenov, A.; Cordes, T.; Herzog, T. T.; Zinth, W.; de Vivie-Riedle, R. Molecular Driving Forces for Z/E Isomerization Mediated by Heteroatoms: The Example Hemithioindigo. J. Phys. Chem. A 2010, 114, 13016−13030. (7) Maerz, B.; Wiedbrauk, S.; Oesterling, S.; Samoylova, E.; Nenov, A.; Mayer, P.; de Vivie-Riedle, R.; Zinth, W.; Dube, H. Making fast photoswitches faster–using Hammett analysis to understand the limit

1590


Letter


(27) Wiedbrauk, S.; Maerz, B.; Samoylova, E.; Reiner, A.; Trommer, F.; Mayer, P.; Zinth, W.; Dube, H. Twisted Hemithioindigo Photoswitches: Solvent Polarity Determines the Type of LightInduced Rotations. J. Am. Chem. Soc. 2016, 138, 12219−12227. (28) Rettig, W. TICT states and beyond: Reaction dimensionality and application to photosynthesis. Proc. Indian Acad. Sci. (Chem. Sci.) 1992, 104, 89−104. (29) Kitahara, T.; Fujita, N.; Shinkai, S. Photoresponsive fluorescence color change derived from TICT in an organogel system. Chem. Lett. 2008, 37, 912−913. (30) Cao, C.; Liu, X.; Qiao, Q.; Zhao, M.; Yin, W.; Mao, D.; Zhang, H.; Xu, Z. A twisted-intramolecular-charge-transfer (TICT) based ratiometric fluorescent thermometer with a mega-Stokes shift and a positive temperature coefficient. Chem. Commun. 2014, 50, 15811− 15814. (31) Clark, S. A.; Singh, V.; Vega Mendoza, D.; Margolin, W.; Kool, E. T. Light-Up “Channel Dyes” for Haloalkane-Based Protein Labeling in Vitro and in Bacterial Cells. Bioconjugate Chem. 2016, 27, 2839− 2843. (32) Deol, H.; Pramanik, S.; Kumar, M.; Khan, I. A.; Bhalla, V. Supramolecular Ensemble of a TICT-AIEE Active Pyrazine Derivative and CuO NPs: A Potential Photocatalytic System for Sonogashira Couplings. ACS Catal. 2016, 6, 3771−3783. (33) Dong, H.; Wei, Y.; Zhang, W.; Wei, C.; Zhang, C.; Yao, J.; Zhao, Y. S. Broadband Tunable Microlasers Based on Controlled Intramolecular Charge-Transfer Process in Organic Supramolecular Microcrystals. J. Am. Chem. Soc. 2016, 138, 1118−1121. (34) Ren, M.; Deng, B.; Kong, X.; Zhou, K.; Liu, K. S.; Xu, G.; Lin, W. A TICT-based fluorescent probe for rapid and specific detection of hydrogen sulfide and its bio-imaging applications. Chem. Commun. 2016, 52, 6415−6418. (35) Sasaki, S.; Drummen, G. P. C.; Konishi, G.-i. Recent advances in twisted intramolecular charge transfer (TICT) fluorescence and related phenomena in materials chemistry. J. Mater. Chem. C 2016, 4, 2731−2743. (36) Maus, M.; Rettig, W.; et al. Photoinduced Intramolecular Charge Transfer in a Series of Differently Twisted Donor-Acceptor Biphenyls As Revealed by Fluorescence. J. Phys. Chem. A 1999, 103, 3388−3401. (37) Rosenfield, R. E., Jr.; Parthasarathy, R.; Dunitz, J. D. Directional Preferences of Nonbonded Atomic Contacts with Divalent Sulfur. 1. Electrophiles and Nucleophiles. J. Am. Chem. Soc. 1977, 99, 4860− 4862. (38) Iwaoka, M.; Isozumi, N. Hypervalent Nonbonded Interactions of a Divalent Sulfur Atom. Implications in Protein Architecture and the Functions. Molecules 2012, 17, 7266−7283. (39) Scheiner, S. Sensitivity of noncovalent bonds to intermolecular separation: hydrogen, halogen, chalcogen, and pnicogen bonds. CrystEngComm 2013, 15, 3119−3124. (40) Adhikari, U.; Scheiner, S. Effects of charge and substituent on the S···N chalcogen bond. J. Phys. Chem. A 2014, 118, 3183−3192. (41) Zhou, F.; Liu, R.; Li, P.; Zhang, H. On the properties of S···O and S···π noncovalent interactions: the analysis of geometry, interaction energy and electron density. New J. Chem. 2015, 39, 1611−1618. (42) Beno, B. R.; Yeung, K. S.; Bartberger, M. D.; Pennington, L. D.; Meanwell, N. A. A Survey of the Role of Noncovalent Sulfur Interactions in Drug Design. J. Med. Chem. 2015, 58, 4383−4438. (43) Hudson, B. M.; Nguyen, E.; Tantillo, D. J. The influence of intramolecular sulfur-lone pair interactions on small-molecule drug design and receptor binding. Org. Biomol. Chem. 2016, 14, 3975−80. (44) Cordes, T.; Weinrich, D.; Kempa, S.; Riesselmann, K.; Herre, S.; Hoppmann, C.; Rück-Braun, K.; Zinth, W. Hemithioindigo-based photoswitches as ultrafast light trigger in chromopeptides. Chem. Phys. Lett. 2006, 428, 167−173. (45) Cordes, T.; Elsner, C.; Herzog, T. T.; Hoppmann, C.; Schadendorf, T.; Summerer, W.; Rück-Braun, K.; Zinth, W. Ultrafast Hemithioindigo-based peptide-switches. Chem. Phys. 2009, 358, 103− 110.

of donor-acceptor approaches for faster hemithioindigo photoswitches. Chem. - Eur. J. 2014, 20, 13984−13992. (8) Eggers, K.; Fyles, T. M.; Montoya-Pelaez, P. J. Synthesis and Characterization of Photoswitchable Lipids Containing Hemithioindigo Chromophores. J. Org. Chem. 2001, 66, 2966−2977. (9) Fullbeck, M.; Michalsky, E.; Jaeger, I. S.; Henklein, P.; Kuhn, H.; Rück-Braun, K.; Preissner, R. Design and biological evaluation of photo-switchable inhibitors. Genome Inform 2006, 17, 141−151. (10) Regner, N.; Herzog, T. T.; Haiser, K.; Hoppmann, C.; Beyermann, M.; Sauermann, J.; Engelhard, M.; Cordes, T.; RückBraun, K.; Zinth, W. Light-switchable hemithioindigo-hemistilbenecontaining peptides: ultrafast spectroscopy of the Z –> E isomerization of the chromophore and the structural dynamics of the peptide moiety. J. Phys. Chem. B 2012, 116, 4181−4191. (11) Kitzig, S.; Thilemann, M.; Cordes, T.; Rück-Braun, K. LightSwitchable Peptides with a Hemithioindigo Unit: Peptide Design, Photochromism, and Optical Spectroscopy. ChemPhysChem 2016, 17, 1252−1263. (12) Tanaka, K.; Taguchi, K.; Iwata, S.; Irie, T. Application of Benzoyl-substituted Hemithioindigo as a Molecular Switch in Porphyrin-Quinone Recognition. Supramol. Chem. 2005, 17, 637−642. (13) Tanaka, K.; Kohayakawa, K.; Iwata, S.; Irie, T. Application of 2Pyridyl-Substituted Hemithioindigo as a Molecular Switch in Hydrogen-Bonded Porphyrins. J. Org. Chem. 2008, 73, 3768−3774. (14) Dube, H.; Rebek, J., Jr. Selective guest exchange in encapsulation complexes using light of different wavelenghts. Angew. Chem., Int. Ed. 2012, 51, 3207−3210. (15) Guentner, M.; Uhl, E.; Mayer, P.; Dube, H. Photocontrol of Polar Aromatic Interactions by a Bis-Hemithioindigo Based Helical Receptor. Chem. - Eur. J. 2016, 22, 16433−16436. (16) Guentner, M.; Schildhauer, M.; Thumser, S.; Mayer, P.; Stephenson, D.; Mayer, P. J.; Dube, H. Sunlight-powered kHz rotation of a hemithioindigo-based molecular motor. Nat. Commun. 2015, 6, 8406. (17) Lippert, E.; Lüder, W.; Boos, H. Adv. Mol. Spectrosc. Proc. Int. Meet. 4th 1959 1962, 443. (18) Rotkiewicz, K.; Grellmann, K. H.; Grabowski, Z. R. Reinterpretation of the Anomalous Fluorescence of p-N,N-Dimethylamino-Benzonitrile. Chem. Phys. Lett. 1973, 19, 315−318. (19) Rettig, W. Charge Separation in Excited States of Decoupled Systems-TICT Compounds and Implications Regarding the Development of New Laser Dyes and the Primary Processes of Vision and Photosynthesis. Angew. Chem., Int. Ed. Engl. 1986, 25, 971−988. (20) Grabowski, Z. R.; Rotkiewicz, K.; Rettig, W. Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures. Chem. Rev. 2003, 103, 3899−4031. (21) Yang, J.-S.; Liau, K.-L.; Wang, C.-M.; Hwang, C.-Y. SubstituentDependent Photoinduced Intramolecular Charge Transfer in N-ArylSubstituted trans-4-Aminostilbenes. J. Am. Chem. Soc. 2004, 126, 12325−12335. (22) Yang, J.-S.; Liau, K.-L.; Hwang, C.-Y.; Wang, C.-M. Photoinduced Single- versus Double-Bond Torsion in Donor-AcceptorSubstituted trans-Stilbenes. J. Phys. Chem. A 2006, 110, 8003−8010. (23) Yang, J.-S.; Lin, C.-K.; Lahoti, A. M.; Tseng, C.-K.; Liu, Y.-H.; Lee, G.-H.; Peng, S.-M. Effect of Ground-State Twisting on the trans to cis Photoisomerization and TICT State Formation of Aminostilbenes. J. Phys. Chem. A 2009, 113, 4868−4877. (24) Yang, J.-S.; Lin, C.-J. Fate of photoexcited trans-aminostilbenes. J. Photochem. Photobiol., A 2015, 312, 107−120. (25) Mukherjee, P.; Rafiq, S.; Sen, P. Dual relaxation channel in thioflavin-T: An ultrafast spectroscopic study. J. Photochem. Photobiol., A 2016, 328, 136−147. (26) Panchenko, P. A.; Arkhipova, A. N.; Fedorova, O. A.; Fedorov, Y. V.; Zakharko, M. A.; Arkhipov, D. E.; Jonusauskas, G. Controlling photophysics of styrylnaphthalimides through TICT, fluorescence and E,Z-photoisomerization interplay. Phys. Chem. Chem. Phys. 2017, 19, 1244−1256. 1591


Letter

The Journal of Physical Chemistry Letters (46) Zander, M.; Rettig, W. Fluorescence Studies on Solvent-Induced Intramolecular Charge Separation in Symmetric Biaryls. Chem. Phys. Lett. 1984, 110, 602−610. (47) Bunte, R.; Gundermann, K.-D.; Leitich, J.; Polansky, O. E.; Zander, M. Synthesis and Twisted Intramolecular Charge Transfer(TICT)-Fluorescence of 8,8′-Bi-naphtho[ 1,2,3,4-def ]chrysenyl. Chem. Ber. 1986, 119, 1683−1688. (48) Rurack, K.; Dekhtyar, M. L.; Bricks, J. L.; Resch-Genger, U.; Rettig, W. Quantum Yield Switching of Fluorescence by Selectively Bridging Single and Double Bonds in Chalcones: Involvement of Two Different Types of Conical Intersections. J. Phys. Chem. A 1999, 103, 9626−9635.

1592


Ingredients to TICT Formation in Donor Substituted Hemithioindigo

Recommend Documents