Published on Web 07/29/2008
Molecular All-Photonic Encoder-Decoder Joakim Andre´asson,*,† Stephen D. Straight,‡ Thomas A. Moore,*,‡ Ana L. Moore,*,‡ and Devens Gust*,‡ Department of Chemical and Biological Engineering, Chalmers UniVersity of Technology, SE-412 96 Go¨teborg, Sweden, and Department of Chemistry and Biochemistry, Arizona State UniVersity, Tempe, Arizona 85287-1604 Received April 17, 2008; E-mail:
[email protected];
[email protected];
[email protected];
[email protected] Abstract: In data processing, an encoder can compress digital information for transmission or storage, whereas a decoder recovers the information in its original form. We report a molecular triad consisting of a dithienylethene covalently linked to two fulgimide photochromes that performs as an all-photonic singlebit 4-to-2 encoder and 2-to-4 decoder. The encoder compresses the information contained in the four inputs into two outputs. The inputs are light of four different wavelengths that photoisomerize the fulgimide, dithienylethene, or both. The outputs are absorbance at two wavelengths. The two decoder inputs are excitation at two wavelengths, whereas the four outputs, which recover the information compressed into the inputs, are absorbance at two wavelengths, transmittance at one wavelength, and fluorescence emission. The molecule can be cycled through numerous encoder and decoder functions without significant photodecomposition. Molecular photonic encoders and decoders could potentially be used for labeling and tracking of nano- and microscale objects as well as for data manipulation.
Introduction
It is becoming well-established that because some molecules can act as reversible switches in response to stimuli, they can be used to perform digital data-processing functions, much as is done by the transistor switches in conventional electronics. Molecular switches, Boolean logic gates, and other data manipulation devices have been described.1–11 Although most of the initial reports of such systems were of simple switches or single-function logic gates, more recent work has produced molecules or mixtures of molecules capable of performing a variety of logic functions.12–19 Most often, these systems use †
Chalmers University of Technology. Arizona State University. (1) Ball, P. Nature (London, U.K.) 2000, 406, 118–120. (2) Magri, D. C.; Vance, T. P.; de Silva, A. P. Inorg. Chim. Acta 2007, 360, 751–764. (3) Tian, H.; Wang, Q. C. Chem. Soc. ReV. 2006, 35, 361–374. (4) Venturi, M.; Balzani, V.; Ballardini, R.; Credi, A.; Gandolfi, M. T. Int. J. Photoenergy 2004, 6, 1–10. (5) de Silva, A. P.; Uchiyama, S. Nat. Nanotechnol. 2007, 2, 399–410. (6) de Silva, A. P.; Uchiyama, S.; Vance, T. P.; Wannalerse, B. Coord. Chem. ReV. 2007, 251, 1623–1632. (7) Balzani, V.; Credi, A.; Venturi, M. ChemPhysChem 2003, 3, 49–59. (8) Credi, A. Angew. Chem., Int. Ed. 2007, 46, 5472–5475. (9) Brown, G. J.; de Silva, A. P.; Pagliari, S. Chem. Commun. (Cambridge U.K.) 2002, 2461–2463. (10) Pischel, U. Angew. Chem., Int. Ed. 2007, 46, 4026–4040. (11) Raymo, F. M.; Giordani, S. J. Am. Chem. Soc. 2001, 123, 4651–4652. (12) Niazov, T.; Baron, R.; Katz, E.; Lioubashevski, O.; Willner, I. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 17160–17163. (13) Margulies, D.; Melman, G.; Felder, C. E.; Arad-Yellin, R.; Shanzer, A. J. Am. Chem. Soc. 2004, 126, 15400–15401. (14) Liu, Y.; Jiang, W.; Zhang, H. Y.; Li, C. J. J. Phys. Chem. B 2006, 110, 14231–14235. (15) Baron, R.; Lioubashevski, O.; Katz, E.; Niazov, T.; Willner, I. J. Phys. Chem. A 2006, 110, 8451–8456. (16) Margulies, D.; Felder, C. E.; Melman, G.; Shanzer, A. J. Am. Chem. Soc. 2007, 129, 347–354. ‡
11122
9
J. AM. CHEM. SOC. 2008, 130, 11122–11128
Table 1. Truth Table for the 4-to-2 Encoder input I0
1 0 0 0
input I1
input I2
input I3
output O1
output O0
0 1 0 0
0 0 1 0
0 0 0 1
0 0 1 1
0 1 0 1
one or more chemical inputs. We have been investigating the use of light as inputs and outputs, usually via photochromes that interact photochemically or photophysically with attached chromophores. Photochromes are photochemical switches that may be photoisomerized back and forth between two (meta)stable states.20 Recent implementations include a half-adder,21 2:1 digital multiplexer,22 and 1:2 demultiplexer.23 A digital encoder converts data into a code. One reason to do this is to compress information for transmission or storage. Consider, for example, the single-bit 4-to-2 encoder, whose truth table is shown in Table 1. The encoder converts 4 bits of data (17) Frezza, B. M.; Cockroft, S. L.; Ghadiri, M. R. J. Am. Chem. Soc. 2007, 129, 14875–14879. (18) Browne, W. R.; De Jong, J. J. D.; Kudernac, T.; Walko, M.; Lucas, L. N.; Uchida, K.; van Esch, J. H.; Feringa, B. L. Chem.sEur. J. 2005, 11, 6414–6429. (19) Strack, G.; Ornatska, M.; Pita, M.; Katz, E. J. Am. Chem. Soc. 2008, 130, 4234–4235. (20) Gust, D.; Moore, T. A.; Moore, A. L. Chem. Commun. (Cambridge U.K.) 2006, 2006, 1169–1178. (21) Andre´asson, J.; Straight, S. D.; Kodis, G.; Park, C.-D.; Hambourger, M.; Gervaldo, M.; Albinsson, B.; Moore, T. A.; Moore, A. L.; Gust, D. J. Am. Chem. Soc. 2006, 12, 16259–16265. (22) Andre´asson, J.; Straight, S. D.; Bandyopadhyay, S.; Mitchell, R. H.; Moore, T. A.; Moore, A. L.; Gust, D. Angew. Chem., Int. Ed. 2007, 46, 958–961. (23) Andre´asson, J.; Straight, S. D.; Bandyopadhyay, S.; Mitchell, R. H.; Moore, T. A.; Moore, A. L.; Gust, D. J. Phys. Chem. C 2007, 111, 14274–14278. 10.1021/ja802845z CCC: $40.75 2008 American Chemical Society
Molecular All-Photonic Encoder-Decoder
ARTICLES
Figure 2. Structures of fulgimide (2) and dithienylethene (3) model
compounds in the open (left) and closed (right) forms. Although the molecules used in this study were racemic, only one enantiomer is shown in the figure.
Figure 1. Structures of triad encoder/decoder 1 with all photochromes in the open states that absorb only UV light (a) and in the closed, cyclic states that absorb in the visible (b). The designations FG and DTE indicate fulgimide and dithienylethene moieties, respectively. Although the molecules used in this study were mixtures of racemic compounds, only one enantiomer is shown in the figure.
into 2 bits. Each of the four inputs, I0-I3, can assume a value of either 0 or 1. The two outputs, O0 and O1 comprise a 2-bit binary number (0, 1, 2, or 3 in base-10 mathematics), where O0 is the sum digit and O1 is the carry digit. A decoder converts the compressed data back into the original form. Here, we report molecular triad 1 (Figure 1), which performs as an all-photonic 4-to-2 encoder and 2-to-4 decoder. The molecule consists of a dithienylethene (DTE) photochrome covalently linked to two fulgimide (FG) photochromic moieties. The two kinds of photochromes may be isomerized independently by different wavelengths of light between closed forms which are colored in the visible (Figure 1b) and open, UVabsorbing forms (Figure 1a). The DTE and FG also have absorption maxima at different wavelengths in both the open and closed forms. The closed form of the fulgimide is fluorescent, but when the dithienylethene is also in the closed form, the fulgimide fluorescence is strongly quenched by intramolecular processes. These properties allow the triad to act as either a 4-to-2 encoder or a 2-to-4 decoder, depending upon the nature of the photonic inputs and outputs, as explained in detail below. Results and Discussion
The synthesis and characterization of triad 1 and its precursors and the details of the spectroscopic measurements are given in the Experimental Section. Here, we will first discuss the photochemistry of two model compounds and then that of the triad. Finally, we will show how these photochemical properties can be employed to achieve the encoder and decoder functions.
Figure 3. Absorption spectra of 2-methyltetrahydrofuran solutions of model
compounds 2o (O), 3o (9), 2c (-O-), and 3c (-9-). The spectra have been scaled to represent the relative populations of chromophores in 1.
Model Compound Spectroscopy. Model FG 2 and DTE 3 (Figure 2) have been previously reported.24 Fulgimide 2o, in the open form, exists as a mixture of E- and Z-isomers that absorb maximally at 380 nm in 2-methyltetrahydrofuran (Figure 3). Irradiation with UV light (e.g., 397 nm) leads to isomerization between the E- and Z-forms and cyclization of the E-form, ultimately converting the sample to a photostationary distribution greatly enriched in the closed form 2c. This isomer has absorption maxima at 262, 295, and 510 nm). The closed form 2c fluoresces (λmax ) 600 nm), and single-photon-timing experiments have determined that the excited singlet state has a lifetime of 135 ps.25 Irradiation of the closed form with visible light induces photoisomerization back to 2o. Thermal isomerization is not observed on the time scale of these experiments. The model dithienylethene in the open form, 3o (Figure 2) has an absorption maximum at 306 nm, with no absorption in the visible (Figure 3). Irradiation in the UV (e.g., 302 nm) isomerizes 3o to the closed, cyclic form 3c, which has absorption maxima at 274, 335, and 600 nm (Figure 3). Photoisomerization with visible light converts 3c back to 3o, and thermal reversion is not observed. Triad 1 Spectroscopy. Because the triad contains three photochromes, two of which are identical, it can exist in six photoisomeric forms. The absorption spectra of 2-methyltetrahydrofuran solutions highly enriched in each of the isomers of interest for this investigation are shown in Figure 4. (24) Straight, S. D.; Liddell, P. A.; Terazono, Y.; Moore, T. A.; Moore, A. L.; Gust, D. AdV. Funct. Mater. 2007, 17, 777–785. (25) Straight, S. D.; Terazono, Y.; Kodis, G.; Moore, T. A.; Moore, A. L.; Gust, D. Aust. J. Chem. 2006, 59, 170–174. J. AM. CHEM. SOC.
9
VOL. 130, NO. 33, 2008
11123
ARTICLES
Andre´asson et al. Table 2. Time Constants (τ) for Photoisomerization Reactions compd
2o f 2c 2o f 2c 2c f 2o 3o f 3c 3o f 3c 3c f 3o
Figure 4. Absorption spectra of a 2-methytetrahydrofuran solution of triad
1 after irradiation with light to produce solutions very highly enriched in FGo-DTEo (s), FGc-DTEo (O), FGo-DTEc (9), and FGc-DTEc (- - -). Also shown is the fluorescence emission at 630 nm from the fulgimide in FGc-DTEo excited at 500 nm (0).
Irradiation of the solution with broad-band green light (460 < λ < 590 nm) yields the triad in which all three photochromes are in the open forms, which do not absorb in the visible. Absorption maxima are observed at 286 (sh), 331, and 387 (sh) nm. This form of 1 will be abbreviated FGo-DTEo, and we will make no distinction between the two equivalent fulgimides. Two fulgimides, rather than one, were incorporated into the molecule in order to enhance some of the effects described below. Irradiation of the solution at 302 nm, where most of the absorption is due to the DTEo chromophore, yields a solution greatly enriched in FGo-DTEc, which has maxima at 362 and 604 nm. Alternatively, irradiating FGo-DTEo at 397 nm photoisomerizes the fulgimides to the closed form, giving FGc-DTEo. Initially, of course, this irradiation produces molecules in which one fulgimide is in the closed form and one is still open, but continued irradiation yields samples in which most of the fulgimides are closed in the photostationary distribution. This material has absorption maxima at 270, 324, and 511 nm (Figure 4). The figure also shows the fulgimide fluorescence emission spectrum of FGc-DTEo, obtained with 500 nm excitation. The emission maximum is at 630 nm. Finally, if FGo-DTEo is irradiated with both 302 and 397 nm light, the sample is converted to a solution highly enriched in FGc-DTEc. The absorption maxima are at 266, 357, 535, and 598 nm. Figure 4 demonstrates both that it is possible to obtain photostationary distributions very highly enriched in the four photoisomers mentioned above and that the spectra of the triad in its various forms are very similar to linear combinations of the spectra of the model compounds shown in Figure 3. That is, linking the chromophores covalently has not led to strong electronic interactions that influence the absorption spectra. In the photostationary distribution containing mainly the FGc-DTEc form of the triad, the FGc fluorescence that was apparent in the FGc-DTEo form (Figure 4) and in model compound 2c is quenched by 98%. This quenching does not lead to sample degradation or the formation of stable photoproducts. It is most likely due to singlet-singlet energy transfer from FGc to DTEc. The overlap of FGc fluorescence and DTEc absorption is excellent, and the interchromophore separations are such that energy transfer by the Fo¨rster mechanism is expected to be very rapid. Because DTEc is essentially nonfluorescent, energy transfer could not be confirmed by fluorescence excitation spectroscopy. Calculations using Fo¨rster theory (ΦF of FGc ) 0.005, ε600 of DTEc ) 2 × 104 M-1 cm-1, orientation factor κ2 ) 0.67) yield a value for the critical distance R0 of 23 Å. Molecular mechanics modeling of 1 yields 11124
J. AM. CHEM. SOC.
9
VOL. 130, NO. 33, 2008
λ (nm)
τ (s)
compd
λ (nm)
a
397 120 1, FGo-DTE f FGc-DTE 366b 30 1, FGo-DTE f FGc-DTE d green 21 1, FGc-DTEo f FGo-DTEo 302e 4 1, FGc-DTEc f FGo-DTE 366b 47 1, FG-DTEo f FG-DTEc greend 350 1, FG-DTEo f FG-DTEc 1, FG-DTEc f FG-DTEo
a
397 366b greend greend 302e 366b greend
τ (s)
170 6, 100c 22 280 4 25 430
a 1.6 mW/cm2, see the Experimental Section for details. b 1.5 mW/ cm2, see the Experimental Section for details. c The decay was biexponential under these conditions. d 9 mW/cm2, 460 < λ < 590 nm, see the Experimental Section for details. e 1.5 mW/cm2, see the Experimental Section for details.
Table 3. Inputs and Outputs for Encoder Function inputs (I) and outputs (O)
λ (nm)
conditions
I0 and reset I1 I2 I3 O0 O1
460 < λ < 590 nm 397 302 366 475 625
9 mW/cm2, 30 min 1.6 mW/cm2, 4 min 1.5 mW/cm2, 3 s 1.5 mW/cm2, 45 s absorbance absorbance
a center-to-center distance between the chromophores of 13 Å. The resulting predicted energy transfer efficiency is 97%, which is comparable to that observed experimentally. The Fo¨rster calculation predicts that the 135 ps lifetime of the FGc first excited singlet state would be quenched to
