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Pseudo Photochromism Induced Halochromism: Reversible Color Change for Porphyrin Derivatives and Their Molecular Recognition Towards Hydrochlorides

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Pseudo Photochromism Induced Halochromism: Reversible Color Change for Porphyrin Derivatives and Their Molecular Recognition Towards Hydrochlorides Send Orders for Reprints to [email protected] Current Inorganic Chemistry, 2014, 4, 59-67 59 Pseudo Photochromism Induced Halochromism: Reversible Color Change for Porphyrin Derivatives and their Molecular Recognition Towards Hydrochlorides Ya Hong Wu1, Lin Lin Qin1, Yan Yan1,*, Shan Ling Tong1, Yan Wang1, Jing Zhang2, Ling Ling Hu1 1 and Jian Yu 1College of Light Industry & Chemical Engineering, Guangdong University of Technology, Guangzhou 510006, P.R. China; 2College of Chemical Engineering, Zhuhai Campus, Beijing Institute of Technology, Zhuhai 519085, P.R. China Abstract: A series of meso-substituted phenyl porphyrin derivatives were selected for investigating their photochromic behavior in several aryl chloride solutions. After ultraviolet irradiation (UVI, = 360 nm), the solutions’ color changed rapidly and sensitively from pink to bright green; and their pink color can be recovered gradually when the green samples are radiated under visible light (VR, > 500 nm) or placed around diffused light at ambient conditions. Notably this pho- tochromic behavior can be completely stimulated by a halochromic method. A porphyrin H2TMPP 3 was selected as a typical sample for revealing this chromic mechanism, and molecular configuration for the green porphyrin chromophores was proposed based on crystal assembly of H2TPP 1. Finally the sensitive molecular recognition of H2TMPP 3 towards hydrochlorides was examined. Keywords: Halochromism, molecular recognition, photochromism, ultraviolet irradiation, visible radiation. INTRODUCTION Both porphyrin and phthalocyanine components acted as assistant chromospheres to enhance the chromic phenomena Photochromism (phototropy) had been attracting research of the covalently linked groups, but the chromism from these attention for a long time [1, 2]. Phytochromes as signal- macrocyclic molecules themselves were seldom discussed. transducing photoreceptors converted between inactive and After successful preparation of bis(Schiff base substituted active forms in response to different wavelengths of light, phenyl) porphyrins and their relative metal complexes, we and this conversion was used to synchronize plant develop- discovered occasionally that both 5, 15- and 5, 10-bis(Schiff ment to the exigencies of the light environment [3]. Crystals base substituted phenyl) porphyrins (9 and 13) in dichloro- of perfluorocyclopentene derivatives exhibited clearly re- methane solvent changed their color reversibly when they versible color change when they were irradiated alternately were irradiated alternately under ultraviolet and diffused with ultraviolet ( = 365 nm) and visible ( > 500 nm) light, along with reversible transformations in molecular structure light. Detailed research results indicated that almost all of the from open-ring into closed-ring isomers [4]. Conjugated metal-free porphyrins and even a zinc (II) porphyrin 2 porphyrins and phthalocyanines are considered as potential (Scheme 1) exhibited the photochromic property. optical limiters [5], molecular switches [6, 7] and photoin- duced electron transfer (PET) [8]. The photochromic behav- EXPERIMENTAL ior of active components was remarkably enhanced by the Measurements: 1H-NMR spectra were recorded with a covalently linked porphyrin chromospheres and their photo- Varian Mercury-Plus 300 FT-NMR (300 MHz) spectrometer chromic mechanism can be easily monitored by reversibly in chloroform-d with tetramethylsilane (Me4Si) as an internal spectral change of the conjugated porphyrin moiety [9, 10]. standard. Chemical shifts () and coupling constants (J) are Macrocyclic phthalocyanine and porphyrin moieties with given in parts per million and hertz respectively. Infrared characteristically pohoinduced spectral properties provided spectroscopy (IR) spectra were performed using an Avatar switching behavior upon photochromic reactions [11-17]. 370 FT-IR spectrometer (Thermo Nicolet). The ultraviolet- “Photochromism” was simply defined as a light-induced visible (UV-Vis) spectra were measured by a Shimadzu UV- reversible change of color; “Halochromism” or “Acidi- 2450 spectrophotometer, using quartz substrates. EPR spec- chromism” was the reversible color change due to a change tra were acquired with a Bruker A200-9.5/12 spectrometer. in pH of a solution. Halochromism can occur in addition to RF powers ranged from 200 to 400 W across the 7 MHz photochromism [18]. scanned range, and microwave power ranged from 2 to 20 mW. The in situ experiments of ultraviolet irradiation (UVI) and visible radiation (VR) were carried out by using a deute- *Address correspondence to this author at the College of Light Industry & rium light source (30W, Lot Oriel Company, Germany) and Chemical Engineering, Guangdong University of Technology, Guangzhou 510006, P.R. China; Tel: +86-15014225076; Fax: +86-20-39322428; a halogen-tungsten light source (1000 W, Lot Oriel Com- Emails: [email protected] and [email protected] pany, Germany). In photochromic determinations, the dis- 1877-945X/14 $58.00+.00 © 2014 Bentham Science Publishers 60 Current Inorganic Chemistry, 2014, Vol. 4, No. 1 Wu et al. 3 tance between light source and sample was set as 20 cm 9.0410 ) and four Q bands (max, Q1 = 516 nm, Q1 = 4 4 (with 0.5 cm slit for UV-Vis determinations and 0.2 mm slit 3.510 ; max, Q2 = 552 nm, Q2 = 1.810 ; max, Q3 = 593 nm, 4 4 for EPR determinations). X-ray data collections and structure Q3 = 1.110 ; and max, Q4 = 648 nm, Q4 = 1.210 ). Both determinations were performed on a Bruker SMART CCD. spectral shape and absorbing position for H2TMPP 3 The data were collected using graphite-monochromatic Mo- changed rapidly due to UVI ( =360 nm, 0.0~20 s): the Soret K radiation ( = 0.71073 Å). The crystal structure was band at 419 nm and three Q bands, including Q1, Q2 and Q3 solved by direct methods and refined by full-matrix least- were disappearing fleetly; and a new Soret band was emerg- 2 square calculation on F with SHELX-97 program package ing demonstrably with red shift (max, Soret 2 = 447.5 nm, Soret 5 [19]. All non-hydrogen atoms were treated anisotropically. 2 = 8.7110 ); meanwhile the Q4 band was much enhanced Hydrogen atoms were placed in calculated positions. and widened out with strong red shift (max, Q4 = 672.5 nm, 5 R2 R3 Q4 = 1.210 ). In a series of changing spectra, an isosbestic point’s appearance at 429.5 nm indicated that a new porphy- N rin species had been formed, and its simplified spectrum N M N with one Soret and one Q band implied that its molecular N configuration had become more symmetrical which resulted from orbital degeneracy increasing and electron transition R1 R4 species decreasing. Within UVI at = 360 nm for 20 s, the sample’s color was changing rapidly from pink to green. More interestingly, when the sample was placed around dif- fused visible light at ambient conditions, its color was recov- ering gradually from green to pink again (Fig. 1-B). This color change was also recovered under visible light radiation 1: H TPP R = R = R = R = -H; M = 2H for bis(Schiff-base substituted) porphyrin 12: H2BBAPBPP 2 1 2 3 4 (Scheme 1) within 12 min when the green sample was being 2: ZnTPP R1= R2 = R3 = R4 = -H; M = Zn(II) radiated under > 500 nm. Therefore it is demonstrably 3: H2TMPP R1= R2 = R3 = R4 = -Me; M = 2H judged that these metal-free porphyrins, and even a zinc- 4: H2TMOPP R1= R2 = R3 = R4 = -OMe; M = 2H porphyrin complex 2: ZnTPP, possessed photochromic prop- 5: H2TAPP R1= R2 = R3 = R4 = -NH2; M = 2H erty with reversible color change, and their photochromic data for reversible color changes were given in Table 1. 6: H2TNPP R1= R2 = R3 = R4 = -NO2; M = 2H 7: H2Tm-NPP R1= R2 = R3 = R4 = m-NO2; M = 2H Notably, when the green sample from ZnTPP 2 was place under diffused visible light, its color changed gradually into 8: H2BAPBPP R1= R2 = -NH2; R3 = R4 = -H; M = 2H the pink one with H2TPP’s characters, which indicated that 9: H2BMBAPBPP R1,R2=-N=CH-p-Me-Ph;R3,R4=-Ph;M=2H ZnTPP 2 was conversed into its free base H2TPP 1 again 10: H2BMOBAPBPP R1,R2=-N=CH-p-MeOPh;R3,R4,M= H (Scheme 2). 11: H BNBAPBPP R ,R =-N=CH-p-NO -Ph;R ,R =-H;M=2H 2 1 2 2 3 4 Meanwhile this photochromic property was greatly af- 12: H2BBAPBPP R1= R2 = -N=CH-Ph; R3 = R4 = -H; M=2H fected by electronic effect from the peripheral substituents. 13: Por-R1-Por R1=-N=CH-Ph-CH=N-;R3,R3,R4=-Ph;M=2H Comparing with the electronic spectra of H2TPP 1 before Scheme 1. The porphyrin derivatives prepared for chromic deter- and after UVI, the electron donating groups, such as -Me (3), minations. -OMe (4) and -NH2 (8), resulted in spectral red shift of Soret bands for their relative porphyrins (entries 1, 3, 4 and 8 in Materials: All chemicals and reagents were used as re- Table 1). But the electron withdrawing groups, such as -m- ceived from commercial sources without purification. Alkyl NO2 (7) and -p-NO2 (6), also resulted in red shift in their chloride solvents for photochromic and halochromic experi- spectral positions of the related porphyrins. Therefore the ments were purified in turns by reflux over anhydrous cal- substituted phenyls in meso-positions around porphyrin cium carbonate and sodium hydroxide, and vacuum distilla- chromospheres mainly contributed electron donating effect tion. Chemical reactions were carried out under an argon by conjugating model. Based on the absorbing positions of atmosphere. The meso-tetra (substituted phenyl) porphyrin Soret bands, the electron donating effects were ranked in derivatives 1-4, 6 and 7 were prepared according to literature order of Phenyl < p-MePhenyl < m-NO2Phenyl p- methods [20, 21]. H2TNPP 6 was reduced by SnCl2·2H2O in MeOPhenyl < p-NO2Phenyl < p-NH2Phenyl (Table 1 and in concentrated HCl solution to give high purity of meso-tetra Supporting Materials: Fig. 5). Therefore the electronic effect (p-aminophenyl) porphyrin (H2TAPP 5) in yield of 80% in these porphyrin derivatives should be considered as the [22].
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