Article pubs.acs.org/JPCC
Light- and Redox-Controlled Fluorescent Switch Based on a Perylenediimide−Dithienylethene Dyad Rafael S. Sánchez, Roser Gras-Charles, José Luis Bourdelande, Gonzalo Guirado,* and Jordi Hernando* Departament de Química, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain S Supporting Information *
ABSTRACT: The development of luminescent materials that are sensitive to both optical and electrical stimuli is of high interest for the fabrication of future information-processing devices. In this study we report about a novel fluorescent molecular switch (1) that can be light- and redox-controlled. This compound has been synthesized by covalent tethering of a perylenediimide fluorophore (PDI) to a dithienylethene (DTE) unit. The photochromic properties of the DTE group are preserved in the dyad, which can be reversibly converted between open (1o) and closed (1c) states upon irradiation. In addition, 1 displays electrochromicity, and its ring-opening process can be promoted quantitatively by electrochemical oxidation. Whereas the open-ring state of the switch is highly fluorescent, the emission of the PDI group in 1c is quenched by energy transfer to the DTE group. This allows large fluorescence modulation between the two states of 1, which can be operated either as an all-optical switch or by a combination of photo- and electrochemical stimuli.
1. INTRODUCTION Owing to the noninvasive character and high selectivity and sensitivity of fluorescence detection, the development of luminescent materials responding to external stimuli has emerged as an important area of research with application in (bio)chemical sensing and imaging,1−4 and information processing and storage.5−7 One of the challenges in this field consists of the preparation of systems that are sensitive to two or more different inputs, thus allowing multifunctionality for a single material. For instance, this would enable complex logic-gate operation5,6,8−10and multimode data storage with increased information density.11−13 To date a limited number of highly fluorescent multistimuli-responsive compounds have been reported,14 which have been designed to be sensitive to different groups of external inputs, such as chemical and optical,10,15 chemical and electrical,16−20 or optical and electrical stimuli.21 In this work our attention focuses on fluorescent compounds that are light- and redox-addressable due to their interest for the fabrication of future information-processing devices.11−13 The design of materials responding to optical and electrical stimuli typically requires the combined use of photo- and electroactive units. In some cases, however, both photo- and electrosensitivity can be attained with a single compound. This is the case of fulgides,22,23 dihydropyrenes,24,25 dithienylethenes (DTEs),26 dithiazolylethenes,27 and polyoxometalates,28 which are well-known photo- and electrochromic switches. Among them, DTEs have been proposed as one of the most promising materials for applications in optoelectronics because of their outstanding photochemical properties, which include highly efficient, fatigue resistant, and reversible photoisomerization between its thermally stable open- and closed-ring isomers.29 In addition, DTEs display a rich electrochromic behavior that has © 2012 American Chemical Society
been profusely investigated in the last years. On one hand, they can undergo intrinsic oxidative ring-closing or ring-opening30−43 and reductive ring-closing reactions.41,44 Moreover, the electrodriven isomerization of DTEs can be modulated by appending redox-active units.44−49 In spite of this, to our knowledge no attempt has been carried out so far to exploit the photo- and electrochromic properties of DTE in order to prepare a lightand redox-controlled highly fluorescent compound based on this material. As a result of the intrinsic low fluorescence quantum yields of DTEs as well as to minimize destructive readout, highly luminescent switches based on dithienylethenes are typically prepared by attaching one or more fluorescent moieties to these units.50 A wide variety of fluorophores have been used with this aim, ranging from luminescent metal complexes51 to a number of different organic fluorophores such as anthracene,7,52,53 coumarin,54 fluorescein,55 porphyrin,56,57 or perylenediimide (PDI).58−63 Herein we have used the same approach to prepare the potential photo- and electroresponsive fluorescent compound 1, which consists of a PDI−DTE dyad presenting mutually interconverting open- and closed-ring isomers (Scheme 1). The choice of the fluorophore and DTE units in 1 has been carried out on the basis of their particular electro-optical properties, which should allow for (i) large emission intensity modulation between the two states of 1 due to the intrinsic high fluorescence quantum yield (Φf ≈ 1) of the PDI group selected64 and its ability to undergo photoinduced energy and electron transfer with close-by DTE units58−63 and (ii) selective access Received: January 25, 2012 Revised: March 1, 2012 Published: March 7, 2012 7164
dx.doi.org/10.1021/jp300815p | J. Phys. Chem. C 2012, 116, 7164−7172
The Journal of Physical Chemistry C
Article
to the closed-ring DTE oxidation wave36 and PDI reduction waves64 in order to promote oxidative ring opening and reductive ring closing of 1.
and subsequent purification, and they were characterized by means of 1H NMR spectroscopy, as described in the Supporting Information. The photostationary state conversions were determined by deconvolution of the UV−vis absorption spectra of the PSS mixtures with those previously measured for pure samples of the open- and ring-closed isomers in the same solvent. The photoisomerization quantum yields were determined using the methodology reported in ref 66 and 1,2-bis(5-chloro2-methylthien-3-yl)perfluorocyclopentene as reference compound (Φo→c = 0.47 and Φc→o= 0.13 in hexane).67 Briefly, solutions of the compound of interest and the reference were irradiated under the same experimental conditions, and the kinetics of the photoreaction was monitored by means of UV−vis spectroscopy, which allowed determining the concentration of the open- and closedring isomers at any time. 2.3. Electrochemical Characterization. Cyclic voltammograms were registered using a VSP100 BIOLOGIC potentiostat and a conical electrochemical cell equipped with an argon bubbling source for degassing, a glassy carbon electrode (WE, d = 1 mm), an auxiliary platinum electrode (CE, d = 1 mm), and a saturated calomel electrode (SCE, RE). All the potentials are reported versus a SCE isolated from the working electrode by a salt bridge. All measurements were performed in CH2Cl2 or acetonitrile solution containing 0.1 M n-Bu4NPF6 as supporting electrolyte. Spectroelectrochemical experiments were carried out using a VSP100 potentiostat synchronized with a L10290 Hamamatsu spectrophotometer and a quartz cuvette (optical path = 1 mm) equipped with a transparent platinum mesh as working electrode (WE), a platinum filament as counter electrode (CE), and a SCE (RE) as reference electrode. All samples investigated were previously degassed with an argon flow. Electrolysis experiments at controlled potentials were undertaken with a EG&G Princeton Applied Research (PAR) 273A potentiostat and an electrochemical cell equipped with an argon bubbling source, a carbon graphite rod, an auxiliary platinum electrode, and a SCE reference electrode. All experiments were performed in CH2Cl2 or acetonotrile solutions containing n-Bu4NPF6 (0.1 M) as supporting electrolyte.
2. EXPERIMENTAL SECTION 2.1. Synthesis. A detailed description of the synthetic procedures used to prepare the fluorescent molecular switch 1 is given in the Supporting Information. 2.2. Optical Characterization. UV−vis spectra were recorded at room temperature using a HP 8452A spectrophotometer (Agilent) with chemstation software. Fluorescence spectra were recorded at room temperature by means of a custom-made spectrofluorimeter, where a Brilliant (Quantel) pulsed laser is used as excitation source and the emitted photons are detected in an Andor ICCD camera coupled to a spectrograph. Fluorescence quantum yields were determined for highly diluted solutions of the compounds of interest to prevent self-absorption processes (absorption
