Light effects in yeast: persisting oscillations in cell division activity and amino acid transport in cultures of Saccharomyces cerevisiae entrained by light-dark cycles.

Abstract— In addition to the direct inhibitory effects of visible light (cool-white fluorescent, < 3500 lux) on growth and amino acid transport previously reported for cultures of the yeast Saccharomyces cereui-siae (strain Y185 rho⁺) grown at 12°C in medium containing glucose, yeast carbon base, KH₂PO₄, ammonium ion and proline, we have found evidence for endogenous, light-entrainable, self-sustaining circadian and ultradian oscillators underlying both cell division and transport activity. Diurnal light (? 3000 lux) cycles (LD), imposed on cultures previously grown in the dark, phased or synchronized cell number increase to a 24-h period with bud release being confined primarily to the dark intervals (although not necessarily every cell divided during any given division ‘burst’). The observed division or budding rhythm freeran with a circadian period (?26h) only approximating 24 h for a number of days in constant darkness (DD) following prior entrainment by LD, thereby implicating an endogenous circadian clock. Further, a similar light-entrainable circadian rhythm in the uptake of “C-histidine or ¹4C-lysine occurred in nondividing (or very slowly dividing) cultures during the “stationary” (infradian) phase of growth synchronized by a 24-h LD cycle and then released into DD for as long as 10 days. Some experiments revealed a bimodal (ultradian) periodicity in both LD and DD with secondary peaks or shoulders occurring at intervals of ?12h, corresponding approximately to subjective ‘dawn’ and ‘dusk’. Transport in cultures of the Y185 rho^- petite mutant, which lacks cytochromes a/a₃, b and c_l, could not be synchronized by LD cycles, a finding that is consistent with the hypothesis that these chromophores may be primary photoreceptors for synchronization of rhythms in this microorganism.     

Mutagenic effects of near ultraviolet and visible radiant energy on continuous cultures of escherichia coli

Abstract— –The induction of mutation to phage T5 resistance by near ultraviolet (u.v.) and visible light was studied in chemostat cultures of Escherichia coli strains B/r and B/r/1, trp. The visible light mutation rate to phage T5 resistance was independent of growth rate over the range studied. This result is consistent with a photochemical mechanism of mutagenesis. Changeovers, in which a faster growing subpopulation takes over the culture, usually causing the mutant frequency to decline sharply, occur more frequently in chemostat cultures irradiated with visible light than in cultures treated with far u.v. or caffeine. A preliminary action spectrum was obtained with aerated chemostats that revealed effective wavelengths to be between 330 nm and 500 nm. Wavelengths longer than 500 nm were not effective. Wavelengths longer than 340 nm were not mutagenic in anaerobic chemostats. This oxygen requirement for mutagenesis between 340 nm and 500 nm is consistent with a photodynamic mechanism of action. In aerated cultures, wavelengths between 400 nm and 500 nm were as effective as wavelengths between 330 nm and 400 nm. A number of naturally occurring compounds, including riboflavin and vitamin K, are consistent with the data as candidates for the chromophore responsible for near u.v. and visible light mutagenesis.     

AN ACTION SPECTRUM IN THE BLUE and ULTRAVIOLET FOR PHOTOTROPISM IN ALFALFA*

Abstract Phototropism is a common property of plants, but it is not known if different species use the same photoreceptor for their response. We have determined fluence-response relations for phototropism in response to brief, broad-band blue irradiation for four plant species grown under red light (Amaranthus paniculatus, Linum usitatissimum, Vigna radiata and Medicago sativa) and compared these to ones previously obtained for Pisum sativum and Zea mays, grown under similar conditions. Curves for all species showed a bell-shaped dependence on fluence, a characteristic of first positive curvature as originally defined for the Avena coleoptile, and had a similar optimal fluence, near 3 H.mol m^?2. We have obtained an action spectrum in the blue and UV spectral regions for first positive phototropism of the hypocotyl of alfalfa grown under red light. Fluence-response curves at wavelengths between 300 and 500 nm were nearly identical in shape and magnitude; whereas below 300 nm, their slopes and maximum curvatures were reduced. The action spectrum showed that activity rose sharply at wavelengths below 500 nm, peaked at 450 nm with shoulders on either side of that peak, and had lesser peaks at 380 and, in the far ultraviolet, at 280 nm. This action spectrum was very similar to ones in the literature (obtained between 350 and 500 nm) for first and second positive phototropism of oat coleoptiles. We conclude that the same photoreceptor mediates phototropism in oat and alfalfa.     

Phytochrome-like responses in Euglena: A low fluence response that reorganizes the spectral dependence of the high irradiance response in long-day photoperiodic induction of cell division

Irradiance spectra change spatiotemporally, and angiosperms adapt accordingly, mainly through phytochromes. This study challenges the long-held belief that the flagellated alga Euglena gracilis lacks phytochromes and is therefore unaffected by spectral changes. We photoautotrophically cultured the alga under continuous light (LL), then transferred it to darkness. After about 26h in darkness, different irradiations for 3h enabled cell division in dark-arrested G2 cells evoking a high-irradiance response (HIR). The spectral characteristics of the irradiation during the LL period (pre-irradiation) defined the spectral sensitivity in the subsequent dark period. LL with light rich in the red spectrum led to a HIR to the red spectrum (R-HIR), whereas light rich in the far-red spectrum (FR) led to a FR-HIR. Finishing the period of pre-irradiation consisting of continuous cool-white fluorescent light (rich in R) by a FR pulse enhanced the characteristics of the FR-HIR 26h later. By contrast, a R pulse given at the end of the pre-irradiation rich in FR potentiated the R-HIR. The effects were completely photoreversible between R and FR with critical fluences of about 2mmolm(-2), satisfying the classic diagnostic feature of phytochromes. The action spectrum of the FR effect at the end of pre-irradiation consisting of continuous cool-white fluorescent light (rich in R) had a main peak at 740nm and a minor peak at 380nm, whereas antagonization of the FR effect had a main peak at 640nm and a minor peak at 480nm. Wavelengths of 610 and 670nm appeared in both spectra. We also demonstrated the photoreversibility of 380/640, 480/740, and (610 and 670)/(640 and 740) nm. We conclude that Euglena displays phytochrome-like responses similar to the 'shade avoidance' and 'end-of-day FR' effects reported in angiosperms.     

BLUE LIGHT EFFECT ON CHLOROPHYLL FORMATION IN CHLORELLA PROTOTHECOIDES

The effectiveness of monochromatic light on chlorophyll formation over a range of 420–80 nm was examined in the regreening cells of Chlorella protothecoides in the presence of chloro-phenyl dimethylurea (CMU). An action spectrum showed two maxima with a minimum near 450 nm. At the most effective wavelength examined (444 nm), 0.2 W. m ^-2 was sufficient for half saturation. The activity of 5-aminolevulinic acid (ALA) production was examined in the greening cells under irradiation with white, blue and red light. The activity was always limited by availability of substrate, especially in the case where the greening cells were incubated with cycloheximide or transferred to darkness. Decay of the activity in these cases was delayed by provision of organic compounds such as glycine, pyruvate or glucose. The effectiveness of blue light on ALA* production observed in the presence of CMU was inferred to be brought about by the increased availability of endogenous substrates.     

ACTION SPECTRA FOR LIGHT-INDUCED DE-EPOXIDATION AND EPOXIDATION OF XANTHOPHYLLS IN SPINACH LEAF*

Abstract— The action spectra for violaxanthin de-epoxidation and zeaxanthin epoxidation in New Zealand spinach leaf segments, Tetragonia expansa, were determined at equal incident quanta of 2·0 × 10¹⁵ quanta cm^-2 sec^-1. Precise action spectra were not obtained due to variable leaf activity. The de-epoxidation action spectrum had major peaks at approximately 480 and 648 nm. Blue light was slightly more effective than red light and little activity was observed beyond 700 nm. The epoxidation action spectrum showed major peaks at around 440 and 670 nm. Blue light was more effective than red light and light beyond 700 nm showed definite activity. The net result of de-epoxidation and epoxidation is a cyclic scheme, the violaxanthin cycle, which consumes O₂ and photoproducts. The action spectra indicate that the violaxanthin cycle is more active in blue than in red light and therefore could account for O₂ uptake stimulated by blue light. However, the violaxanthin cycle is not the pathway for O₂ uptake by photosynthetic system 1. It was suggested that the violaxanthin cycle may function as a pathway for the consumption of excess photoproducts generated in blue light or the conversion of these photo-products to other forms of energy.     

Biphasic fluence-response curves and derived action spectra for light-induced absorbance changes in Phycomyces mycelium

The photoresponses of Phycomyces, including phototropism and photocontrol of sporangiophore development, are mediated primarily by blue and UV light. Recent results on these two responses indicated a subsidiary role for green light. We have measured in vivo light-induced absorbance changes (LIAC) in mycelial samples of a caroteneless (carB) strain to compare the effectiveness of UV, blue, and green light. In the dual-wavelength kinetic mode of the spectrophotometer, measuring wavelengths of 445 and 470 nm were chosen, because green light produces substantial absorbance changes between these two wavelengths. Fluence-response curves were measured for 13 wavelengths between 365 and 530 nm, and for variable exposure times between 0.5 and 320 s. With one exception (365 nm), the curves were biphasic. The low fluence component was generally sigmoidal with an abrupt rise. The high fluence component failed to reach saturation for the fluences tested (less than 70 μmol m⁻² s⁻¹). Using the inferred threshold fluences of these two components as criterion effects, we obtained two action spectra. For the low fluence component, the action spectrum showed major peaks at 394, 450, and 530 nm and a minor peak at 416 nm. The high fluence component action spectrum showed very little sensitivity in the blue region. The major sensitivity was in the near UV, and a relatively small peak appeared in the green part of the spectrum at 507 nm. The biphasic character of the fluence-response curves suggests that two photosystems are responsible for the absorbance changes. The low fluence photosystem is sensitive mainly to blue and UV light and may thus represent a physiological blue-light photoreceptor. The high fluence photosystem is clearly not of this type. It (and perhaps the low fluence system as well) may mediate some of the subsidiary physiological effects of green light.     

Physiological Doses of Red Light Induce IL‐4 Release in Cocultures between Human Keratinocytes and Immune Cells

Phototherapy is routinely used for the treatment of various skin conditions and targeted therapy of superficial cancers. However, the molecular mechanisms behind their biological effects and the need for efficacy enhancing photosensitizers are not well addressed. Particularly, not much is known about the inherent effect of light from the visible spectrum on cytokine release and its downstream effects in keratinocytes and immune cells located in skin and therefore exposed to light. To address this, we delivered calibrated doses of well‐defined light qualities (380 to 660 nm) to cocultures of human keratinocytes and macrophage/dendritic cells in the absence or presence of the commonly used photosensitizer 8‐methoxypsoralen (8‐MOP ). The experiments identified IL ‐4 as a key effector cytokine released by this coculture model with need for 8‐MOP in the UVA₁/blue (380 nm) and no requirement for photosensitizer in the red light spectrum (627 nm). 3D organotypic skin cultures treated with IL ‐4 showed thickening of the epidermal layer and delayed differentiation. However unlike IL ‐4 and UVA₁/blue light treatment, red light did not reduce the expression of keratinocyte differentiation markers or increase signs of photo‐oxidative damage. This supports the application of isolated red light as a possible alternative for photo‐immunotherapy without need for additional photosensitizers.     

Efficient Synthesis of 3‐Phenylnaphtho[2,3‐b]furan‐4,9‐diones in Water and Their Fluorimetric Study in Solutions

A simple and efficient protocol has been developed for the synthesis of 3‐phenylnaphtho[2,3‐b]furan‐4,9‐diones by domino reaction of α‐bromonitroalkenes to 2‐hydroxynaphthalene‐1,4‐dione. With the optimal reaction conditions [NaOAc (120 mol%), water, 70°C, 7 h], the scope of the domino reaction was explored and the green approach provided the desired products in moderate to good yields at elevated temperature under aqueous‐mediated conditions. A mechanistic rationalization for this reaction is also provided. The absorption characteristics of the compounds were examined by UV‐Vis spectra and fluorescence spectroscopy. All compounds were fluorescent in solution emitting at blue light (432–433 nm), green light (512–536 nm), or yellow light (591 nm).     

FLAVIN TYPE ACTION SPECTRUM OF NITRATE UTILIZATION BY Monoraphidium braunii

The light-dependent utilization of nitrate by the green alga Monoraphidium braunii, coming from nocturnal dark periods, shows an action spectrum of flavin type with two main bands: one in the blue, peaking at 450 and 480 nm, and the other in the near-UV region with a maximum at 365 nm. Other results indicate that cells growing on nitrate as the only nitrogen source resynthesize nitrate reductase daily, which implies the nocturnal loss of this enzyme. The biosynthesis of nitrate reductase at the beginning of the light periods can proceed under red light. In addition, blue or near-UV light is required for the activation of the previously formed nitrate reductase.     

THE SENSORY PHOTORECEPTORS OF Halobacterium halobium REVISITED: ACTION SPECTRA and INFLUENCE OF BACKGROUND LIGHT*

Abstract– Action spectra of the light-dependent behavior of Halobacterium and the effect of background light have been measured with regard to the current hypothesis of Spudich and Bogomolni [Nature 312 ,509–513 (1984)], which proposes sensory rhodopsin I (sRI₅₈₇) to be the receptor for long-wavelength light, and its photoproduct S₃₇₃ to be the receptor for UV light. The action spectrum shows three maxima for attractant responses (prolonged swimming intervals) at 565, 590, and 610 nm, and two maxima for repellent responses (shortened intervals) at 370 and 480 nm. The latter is assigned to sensory rhodopsin II (P-480). All peaks are red-shifted after substitution of the endogeneous retinal by 3, 4-dehydroretinal. The peaks at 590 and 610 nm are suppressed by long-wavelength background light. Ultraviolet background light converts all attractant peaks into repellent peaks. The response at 370 nm is strongly activated by visible background light, the maximal effect occurring with 510 nm. The activated state declines with a half-life of about 1.2 s. In a growing culture, full sensitivity to UV and blue light is restored about 10 h earlier than sensitivity to long-wavelength light. Some of the results cannot easily be explained by the sRI₅₈₇/S₃₇₃ hypothesis. Explanations for the three maxima in the long-wavelength range and for the maximal activation of the UV response by 510 nm light are discussed.     

基于席夫碱配体的锰羰基配合物可见光诱导释放一氧化碳性能

利用五羰基溴化锰和2-吡啶甲醛以及卤代苯胺通过一步法合成得到了3个含席夫碱配体的锰羰基配合物[Mn(CO)₃(py(CH=N)ph-X)Br],其中X=Cl (1)、Br (2)、I (3),并采用核磁、X射线单晶衍射、红外光谱、紫外可见光谱和荧光光谱对其进行了表征。这类配合物在非光照下稳定,在可见光(LED蓝光、绿光和红光)作用下分解释放CO,可以作为光诱导的一氧化碳释放剂(photoCORMs)。研究表明蓝光是促进配合物分解释放CO的最有效光源。此外,CO释放动力学分析显示配合物分解释放CO过程符合一级动力学模型。配合物3的释放研究表明脱氧肌红蛋白能够捕捉所释放的CO。尽管这些配合物本身的细胞毒性(IC50)达到微摩尔级,但光照下的细胞兼容性有显著改善,上升为接近100微摩尔级。这些配合物具有荧光性质,在450 nm激发波长下在500～700 nm范围内发射一定强度的荧光,可以作为荧光标记物用以监测细胞或生物体内释放剂分布及CO释放情况。     

BILIRUBIN PHOTOTOXICITY TO HUMAN CELLS BY GREEN LIGHT PHOTOTHERAPY in vitro

Phototherapy of newborn infants with blue or green light is the most common treatment of neonatal hyperbilirubinemia. Using bilirubin bound to human lymphoid and basal skin cells we obtained the green light dose dependency of the bilirubin phototoxicity to these cell types. Cells (3–5× 10⁶/mL) were incubated with bilirubin complexed to human serum albumin (final concentrations 340 μM bilirubin, 150 μM albumin). Under these conditions all cells showed maximum binding of bilirubin. Irradiation with broadband green light (Λ_max= 512 nm) over 24 h led to a light dose-dependent population of cells, which contained no bilirubin on the cell membrane as determined by Nomarski interference microscopy. The light-induced mechanism of the disappearance of bilirubin caused lethal membrane damage to the cells (trypan blue exclusion test). The cell kill rate increased with the irradiation dose and with the fraction of cells with no bilirubin. When 90% of lymphoid cells were bilirubin free, 46% of them were dead (using 480 J cm^?1 green light). Similar results were obtained with basal skin cells. In addition, bilirubin-induced damage of cell membrane and nuclear membrane was also shown by transmission electron microscopy. Bilirubin (340 μM) in the dark led to 5% of the cells being killed. Basal skin cells bind 2.5 times more bilirubin molecules than lymphoid cells and showed a different bilirubin disappearance. Irradiation of bilirubin in carbon tetrachloride with 514.5 nm laser light showed generation of singlet oxygen via its luminescence at 1270 nm. These results demonstrate that green light phototherapy of hyperbilirubinemia may cause both skin and immune system damage.     

Enhancement of color purity in blue light emitting poly(fluorene)s and poly(p‐phenylene)s with 2,6‐distyrylpyridine kinked segments along the backbone

2,6‐bis(4‐Distyrylpyridine) ( 1 ) was synthesized by the condensation of 2,6‐dimethylpyridine with 4‐bromobenzaldehyde. Two new series of soluble random or alternating polyfluorenes ( PF‐Py ) and poly‐p‐phenylenes ( PP‐Py ) with various compositions were prepared by Suzuki coupling utilizing 1 as a comonomer. These polymers showed optical band gaps of 3.00–3.07 eV and photoluminescence (PL) quantum yields in solution of 0.37–0.91 for PF‐Py and 0.29–0.38 for PP‐Py . Polymers PF‐Py emitted blue light with PL maximum at 410–424 nm in solution and 406–428 nm in thin films that was red shifted with increasing distyrylpyridine content. Polymers PP‐Py behaved as blue emitters both in solution and in solid state, with PL maximum at 416–436 nm. The optical properties of these polymers could be tuned by the reversible protonation–deprotonation process of the pyridine ring. The emitted color of the polymers in solution and thin film could be changed continuously between blue and green (PL maximum up to about 520 nm) by exposing the polymers to the acid or base environment. Thin films of PF‐Py displayed excellent color stability with a small red shift of 10 nm but without additional emission band in the long wave region of the spectrum, even after being annealed at high temperature for a long time. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4486–4495, 2005     

Poly(fluorenevinylene) derivatives by Heck coupling: Synthesis,photophysics, and electroluminescence

Three new poly(fluorenevinylene) derivatives were synthesized, characterized, and used as emissive materials in light‐emitting diodes (LEDs). They were synthesized by Heck coupling of 9,9‐dihexyl‐2,7‐divinylfluorene with 2,7‐dibromo‐9,9‐dihexylfluorene, 2,3‐bis(4‐bromophenyl)quinoxaline, or 2,5‐bis(4‐bromophenyl)‐3,4‐diphenylthiophene to afford the polymers F , Q , and T , respectively. Polymers F and Q had medium number–average molecular weights (M_n ? 14,000) with relatively narrow polydispersity (1.3–1.6), while T was obtained as an oligomer (M_n ? 4000). All polymers were soluble in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. They emitted blue‐greenish fluorescence light in dilute THF solution (444–491 nm), with photoluminescence (PL) quantum yields of 0.32–0.54, and in thin film (453–488 nm). LEDs with the configuration of ITO/PEDOT‐PSS/Polymer/Li:Al were fabricated and evaluated. The electroluminescence (EL) spectra of the Q and F polymers were very broad covering the blue–green–red region, whereas the spectrum of the polymer T was almost purely blue. The threshold electrical field for light emission of the devices was almost the same (?1.75 MV/cm). The external quantum efficiency of the devices of polymers Q and F was about 1.0 × 10^?3%, whereas that of polymer T was ?3.0 × 10^?5%. The fluorescence lifetime of polymers F and Q was significantly longer than that of the polymer T . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4494–4507, 2006     

基于席夫碱配体的锰羰基配合物可见光诱导释放一氧化碳性能

利用五羰基溴化锰和2-吡啶甲醛以及卤代苯胺通过一步法合成得到了3个含席夫碱配体的锰羰基配合物[Mn (CO)₃(py (CH=N) ph-X) Br],其中X=Cl (1)、Br (2)、I (3),并采用核磁、X射线单晶衍射、红外光谱、紫外可见光谱和荧光光谱对其进行了表征。这类配合物在非光照下稳定,在可见光(LED蓝光、绿光和红光)作用下分解释放CO,可以作为光诱导的一氧化碳释放剂(photoCORMs)。研究表明蓝光是促进配合物分解释放CO的最有效光源。此外,CO释放动力学分析显示配合物分解释放CO过程符合一级动力学模型。配合物3的释放研究表明脱氧肌红蛋白能够捕捉所释放的CO。尽管这些配合物本身的细胞毒性(IC₅₀)达到微摩尔级,但光照下的细胞兼容性有显著改善,上升为接近100微摩尔级。这些配合物具有荧光性质,在450 nm激发波长下在500~700 nm范围内发射一定强度的荧光,可以作为荧光标记物用以监测细胞或生物体内释放剂分布及CO释放情况。     

LOW TEMPERATURE ABSORBANCE AND FLUORESCENCE SPECTROSCOPY OF THE PHOTOACTIVE YELLOW PROTEIN FROM Ectothiorhodospira halophila

A simplified procedure was developed to purify the photoactive yellow protein (PYP) from Ecrorhiorhodospira halophila. Specific antibodies were used to follow the distribution of PYP through the separate purification steps. Low temperature absorbance and fluorescence characteristics of this photoactive protein were investigated. The absorbance spectrum of PYP in 67% (vol/vol) glycerol peaked at 449 and 447 nm, at room-and liquid nitrogen temperatures, respectively. It sharpened significantly upon cooling to 77 K and displayed fine-structure on the blue side of its absorbance maximum, with a spacing of 25 nm. At room temperature PYP fluoresced with a quantum yield of approximately 3.5 times 10^?-³ an emission maximum of 495 nm. Maximal excitation occurred at 457 nm, 10 nm red-shifted with respect to the absorbance maximum. At -low temperature the excitation maximum remained unaltered but maximal emission shifted significantly to the blue (to 482 nm). The quantum yield of fluorescence increased to 0.07 at this temperature. Illumination of PYP at low temperature with light from the visible part of the spectrum of electromagnetic radiation induced pronounced changes in its absorbance and fluorescence characteristics. At least two new stable intermediates were formed: one highly fluorescent, with an excitation maximum at 430 nm; additionally, a non-fluorescent red-shifted intermediate with an absorbance maximum at 490 nm. The amount formed of these two intermediates depended strongly on the wavelength of actinic illumination. In combination, these data underline the spectroscopic similarities between PYP and the retinal-containing chromoproteins that are present in Halobacterium halobium.     

Synthesis of pure blue emissive poly(2,7‐carbazole)s anchored by electron donor pendant

Three novel poly(2,7‐carbazole)s having hole injection and transporting pendent moieties of carbazole and triphenylamine at the N‐position were synthesized for achieving pure blue electroluminescence. The N‐pendants in the polymers correspond to N‐phenylcarbazol‐2‐yl ( P1 ), N,N‐diphenylamino‐N‐phenylcarabazol‐2‐yl ( P2) , and 4‐phenyl having a hydrocarbon chain with a triphenylamine terminal ( P3 ), respectively. Electronic, optical, and electroluminescence properties of these polymers were compared with those of a poly(2,7‐carbazole) directly connected with triphenylamine at the N‐position ( P0 ) having an aggregation‐induced emissive property. The photoluminescence (PL) spectra suggested that they could emit in the region of blue light in the film state. Especially, P2 that has the fixed and large diphenylaminocarbazolyl pendant showed a deep‐blue fluorescence with CIE(x, y) = (0.15, 0.07). The P0 , P2 , and P3 based light emitting diode devices showed maximum electroluminescence wavelengths in the range of 430–450 nm. The P2 device showed pure blue emission (CIE[x, y] = [0.18, 0.16]), high luminance (1130 cd/m²) and current density (628 mA/cm²) at 8 V, whereas low‐energy emissions around 500–600 nm were emerged at higher than 9 V. The P0 and P3 devices also showed a blue electroluminescence in the range of 8–11 V, but their luminance and efficiency were low. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2526–2534     

Large Thermally Irreversible Photoinduced Shift of Selective Light Reflection in Hydrazone-Containing Cholesteric Polymer Systems

Stimuli responsive liquid crystalline polymers are a unique class of so-called “smart” materials demonstrating various types of mesomorphic structures easily controlled by external fields, including light. In the present work we synthesized and studied a comb-shaped hydrazone-containing copolyacrylate exhibited cholesteric liquid crystalline properties with the pitch length of the helix being tuned under irradiation with light. In the cholesteric phase selective light reflection in the near IR spectral range (1650 nm) was measured and a large blue shift of the reflection peak from 1650 nm to 500 nm was found under blue light (428 or 457 nm) irradiation. This shift is related to the Z-E isomerization of photochromic hydrazone-containing groups and it is photochemically reversible. The improved and faster photo-optical response was found after copolymer doping with 10 wt % of low-molar-mass liquid crystal. It is noteworthy that both, the E and Z isomers of hydrazone photochromic group are thermally stable that enable to achieve a pure photoinduced switch without any dark relaxation at any temperatures. The large photoinduced shift of the selective light reflection, together with thermal bistability, makes such systems promising for applications in photonics.     

Synthesis of chromo‐ and fluorogenic poly(ortho‐diaminophenylene) chemosensors for fluoride anion

Two new poly(ortho‐diaminophenylene) derivatives containing fluorene and/or quinoxaline moieties per repeat unit in the main chain were synthesized via Suzuki coupling reaction followed by reduction process. The synthesized polymers were characterized and explored as colorimetric and fluorometric anion‐sensing materials. The polymers in dilute tetrahydrofuran (THF) solution emitted green light (about 530 nm) in their precursor benzothiadiazole forms and blue to green light (477–523 nm) in their reduced forms. The color of polymer solution was dramatically altered upon addition of fluoride anion without noticeable absorption change in UV–vis spectrum. The fluorescence was ratiometrically quenched with a linear relationship between fluorescence intensity and fluoride anion concentration implying static quenching mechanism could be applied judging from the maintenance of constant fluorescence lifetime with variable fluoride anion concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1546–1556, 2007