Conformational variation and crystalline phase transformation of low syndiotactic polypropylene films in stretched and stress‐relaxed states

Low syndiotactic polypropylene (sPP; rrrr = 80%) films were isothermally crystallized at 0 °C (sample S₀) and 90 °C (sample S₉₀) for 65 h, respectively. Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction were used to characterize the structure transformation and orientation behavior of samples S₀ and S₉₀ at both stretched and stress‐relaxed states. It was found that stretching (λ = 0–700%) induces the transformation of the chain conformation from helical to trans‐planar form for both S₀ and S₉₀ films. The stretched S₀ and S₉₀ samples show well oriented trans‐planar chains as well as partially retained helices. Simultaneously, crystalline phase transformation occurs during the stretching and relaxing processes of the investigated sPP samples, i.e., stable form I crystals can be transformed into metastable form III or mesophase by stretching samples, and vice versa. For stretched S₀ sample, form III with trans‐planar conformation, which generally exists in highly stretched sPP, cannot be observed, even at higher strains. For sample S₉₀, however, stretching might induce the formation of both the form III crystals and mesophase with trans‐planar chains; releasing the tension, form III again gets converted into trans‐planar mesophase and form I crystals. In the stretched and stress‐relaxed states of samples S₀ and S₉₀, the difference of the delicate orientation behavior and relative content of chain conformation and crystalline form can be attributed to the different heat‐treating methods of the low syndiotacticity sPP. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2924–2936, 2005     

Elasticity of syndiotactic polypropylene: Insights from temperature and time dependence

The origin of the unusual and puzzling elasticity of drawn sPP samples was investigated. The mechanism responsible of the elasticity was studied for drawn samples characterized by a very simple structural organization, where there are no involvements of crystallographic modifications with different chain conformation. The elastic behavior of the drawn samples, valued through the hysteresis cycles, was determined at different temperatures. At room temperature the samples show remarkable elastic properties, whereas decreasing the temperature the elastic behavior becomes worse and worse, disappearing at temperatures lower than 0 °C. The elasticity also disappears in drawn samples after a long aging under tension. Thermomechanical and structural investigations, as well as shrinkage as a function of temperature and aging at room temperature of the fixed drawn samples, support the idea that the elastic behavior of sPP can be explained by the model of the plastic deformation of semicrystalline polymers. The interpretation is based on the presence of “tie” molecules axially connecting the crystals in the oriented samples, whose extension, chain conformation and/or crystallization determine the retractive stress of the oriented sample, as well as other mechanical properties. We show that many experiments on the drawn samples, either fixed or relaxed, are strictly connected to the morphology of the drawn sample, derived by the transition between the lamellar initial and the fibrillar final structure. By applying the model we can answer the questions derived from the experimental facts not yet well clarified, giving a new insight into the interesting elasticity of sPP.     

Elastic Behaviour of Oriented Syndiotactic Poly(propylene)

A syndiotactic poly(propylene) film (sPP), quenched from the melt at 0°C, was drawn at room temperature up to a draw ratio of λ = 6. The fibre was analysed under tension by X‐ray analysis and FTIR spectroscopy, showing the presence of the oriented crystalline form III described by Chatani, with the chains in trans‐planar conformation. Then it was unhooked, undergoing a large shrinkage, and reaching a length corresponding to a draw ratio of λ = 3.8. X‐ray and FTIR analysis showed that in the relaxed fibre, a conformational transition from the trans‐planar to the helical form occurred. The relaxed fibre was again submitted to increasing extensions up to λ = 6, step by step, and the elastic behaviour was analysed through the Mullins' curve and hysteresis cycles. It showed good elastic properties, which appear to be closely correlated to the conformational transition between helical and trans‐planar forms.     

The Role of the trans-Planar Mesophase in the Polymorphic Behavior of Syndiotactic Polypropylene

The transformations of the trans-planar mesophase of syndiotactic polypropylene (sPP) subjected to thermal, mechanical and solvent treatments, were investigated. The unoriented trans-planar mesophase, obtained by quenching the melt at 0°C, was annealed at 80°C and the thermal transformation was investigated by X-rays, infrared and dynamic-mechanical analysis. The presence of the helical form II was recognized in the annealed sample. The oriented trans-planar mesophase, obtained by drawing at room temperature and releasing the tension, was immersed in liquid dichloromethane for 24 hours. After drying the sample showed the presence of the oriented form II, although it was not possible to exclude a partial transition into form IV. On the basis of the present and literature results we suggested a scheme of the polymorphic transitions of sPP, in which the central role of the trans-planar mesophase is enlightened.     

Crystallization kinetics and morphology of the mesomorphic form of syndiotactic polypropylene

For the first time the kinetics of formation of syndiotactic polypropylene mesophase close to 0 °C through differential scanning calorimetry has been investigated. The calorimetric data have been analyzed through the well‐known Avrami analysis. We have obtained Avrami coefficients less or at most equal to 2, which are likely to indicate a nearly bidimensionality of the crystallites. The morphology of the mesophase, not known up to now, has been examined through atomic force microscopy (AFM): lamellar structures have been observed. The fractal dimension of the AFM images has been evaluated through the box counting method. It resulted about 2, in a very good agreement with the calculated Avrami coefficients. An infrared and diffractometer analysis on samples kept for increasing times at 0 °C has also been performed to confirm the calorimetric data. The experimental results allow one to better clarify the kinetics of mesophase‐formation. It has been found that a time of 3 h at 0 °C is actually necessary for the complete crystallization of the trans‐planar mesophase, a longer time is needed to stabilize the mesophase domains when the sample is extracted from 0 °C at room temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 936–944, 2007     

Physical aging of syndiotactic polypropylene

Syndiotactic polypropylene (sPP) was quenched from the melt in an ice‐water bath, and changes in the structural organization, during the aging time, were followed by X‐rays, differential scanning calorimetry, and transport properties of dichloromethane at low activities. After 1 month, an increase of crystallinity from 19 to 26% was observed. In addition, the results of sorption and diffusion indicated a consistent increase of an intermediate phase not crystalline, yet impermeable to the vapors. The study of the mechanical properties showed that there is a remarkable increase of all the mechanical parameters with the aging time, and this effect was associated to the increase of the intermediate phase. The elastic modulus increased three times in the first hours of aging. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 173–180, 1999     

Lightly crosslinked,mesomorphic networks obtained through the reaction of dimeric,liquid‐crystalline epoxy–imine monomers and heptanedioic acid

We reacted various dimeric, liquid‐crystalline epoxy–imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid‐crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed‐frequency and frequency‐sweep modes in the shear sandwich configuration. The arrangement in the liquid‐crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid‐crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid‐crystalline phase with respect to side‐chain liquid‐crystalline elastomers and that the time–temperature superposition principle did not hold through the liquid‐crystalline‐to‐isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270–6286, 2006     

Crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline poly(epichlorohydrin) derivatives

We performed the crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline polyethers using peroxide‐type initiators with and without the addition of tertiary amine promoters. The crosslinking temperatures were chosen in the range of mesophase stability to allow the mesophase order to be frozen. The biphenyl derivatives, with a high isotropization temperature, were crosslinked to a large extent. This led to anisotropic thermosets. To crosslink naphthalene derivatives, amine promoters were needed, but degrees of crosslinking were lower, and anisotropic elastomers were obtained. Crosslinking processes were studied by differential scanning calorimetry, polarized optical microscopy, and Fourier transform infrared spectroscopy. The nature of the frozen mesophase was confirmed by X‐ray diffraction studies on mechanically oriented samples. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2237–2244, 2002     

Effects of the oriented mesophase on the cold crystallization of syndiotactic polystyrene and its blend with poly(2,6‐dimethyl‐1,4‐phenylene oxide)

The effects of molecular orientation on the crystallization and polymorphic behaviors of syndiotactic polystyrene (sPS) and sPS/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) blends were studied with wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. The oriented amorphous films of sPS and sPS/PPO blends were crystallized under constraint at crystallization temperatures ranging from 140 to 240°C. The degree of crystallinity was lower in the cold‐crystallized oriented film than in the cold‐crystallized isotropic film. This was in contrast to the case of the cold crystallization of other polymers such as poly(ethylene terephthalate) and isotactic polystyrene, in which the molecular orientation induced crystallization and accelerated crystal growth. It was thought that the oriented mesophase was obtained in drawn films of sPS and that the crystallization of sPS was suppressed in that phase. The WAXD measurements showed that the crystal phase was more ordered in an sPS/PPO blend than in pure sPS under the same annealing conditions. The crystalline order recovered in the cold‐crystallized sPS/PPO blends in comparison with the cold‐crystallized pure sPS because of the decrease in the mesophase content. The crystal forms depended on the crystallization temperature, blend composition, and molecular orientation. Only the α′‐crystalline form was obtained in cold‐crystallized pure sPS, regardless of molecular orientation, whereas α′, α″, and β′ forms coexisted in the cold‐crystallized sPS/PPO blends prepared at higher crystallization temperatures (200–240°C). The β′‐form content was much lower in the oriented sPS/PPO blend than in the isotropic blend sample at the same temperature and composition. It was concluded that the oriented mesophase suppressed the crystallization of the stable β′ form more than that of the metastable α′ and α″ forms during the cold crystallization of sPS/PPO blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1665–1675, 2003     

Side‐chain cholesteric liquid‐crystalline elastomers derived from smectic crosslinking units: Synthesis and phase behavior

New side‐chain cholesteric liquid‐crystalline elastomers containing cholesteryl 4‐allyloxybenzoate as cholesteric mesogenic units and biphenyl 4,4′‐bis(10‐undecen‐1‐ylenate) as smectic crosslinking units were synthesized. The chemical structures of the olefinic compounds and polymers obtained were confirmed by element analysis, Fourier transform infrared, proton nuclear magnetic resonance, and carbon‐13 nuclear magnetic resonance spectra. The mesogenic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the concentration of the crosslinking unit on the phase behavior of the elastomers was examined. The elastomers containing less than 17 mol % of the crosslinking units revealed elasticity, reversible mesomorphic phase transition, wider mesophase temperature ranges, and higher thermal stability. The experimental results demonstrated that the glass‐transition temperature, isotropization temperature, and mesophase temperature ranges decreased with an increasing concentation of the crosslinking unit. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5262–5270, 2004     

Vinyl‐terminated liquid‐crystalline dendrimers based on dendritic polyols and their siloxane‐based elastomers

A new series of side‐chain liquid‐crystalline dendrimers (LCDs) by grafting vinyl‐terminated phenyl benzoate‐based promesogens to a novel polypropyleneimine‐derived dendritic polyols are reported. Polarized optical microscopy and X‐ray diffraction studies show that both the compounds display a smectic‐A (SmA) mesophase. The second‐generation dendrimer bearing eight‐branched promesogens exhibits a more stable SmA mesophase with a wide mesomorphic temperature range. It is demonstrated that “promoting groups” in the structure of LCD for the enhancement of mesomorphic stability are unnecessary in the case of strong anisotropic interactions. In contrast to conventional LCDs, these two compounds possess reactive vinyl terminals that endow them with the potential for the preparation of polymeric materials. For the first time, a type of thermoset elastomers is explored from LCDs via hydrosilylation crosslinking reaction of vinyl terminals and siloxane crosslinker. Two‐dimensional X‐ray diffraction study indicates that the lamellar structures of original dendrimers are reserved in the elastomer networks. Stress–strain curves reveal that these elastomers exhibit excellent elasticity under successive uniaxial compression. The combination of anisotropic structures of rigid units and elasticity of flexible networks in this novel series of elastomers makes them promising candidates for the application in artificial muscles or cartilages. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999     

FTIR spectroscopic investigation of thermal effects in semi‐syndiotactic polypropylene

The temperature‐dependent behavior of individual components within metallocene‐catalyzed semisyndiotactic polypropylenes (semi‐sPP) with a wide range of stereoregular content (26 to 96% rr) is studied using Fourier transform infrared (FTIR) spectroscopy and temperature‐modulated differential scanning calorimetry (DSC). Changes in sensitive, high‐resolution absorbance spectra are observed as melt‐slow‐cooled thin films are subjected to stepwise temperature increases. In general, spectral bands previously identified as being sensitive to ordered structures (e.g., conformed chains, crystal morphs) appear to follow overall trends of shifting to lower wavenumbers (energies), broadening, and decreasing in peak area intensity as temperature increases. Peaks that appear due to “splitting” (observed in more stereoregular materials) show a trend toward coalescence as temperature increases; this corresponds to a gradual loss of chain conformational order. Gauche‐gauche‐trans‐trans (ggtt)_n helical and all‐trans (tttt)_n planar zigzag‐conformed chains that participate in the crystalline‐amorphous interfacial region (“mesophase”) appear to be more stable (i.e., they do not lose their conformational order as easily) with increasing temperature in materials with a greater degree of syndiotacticity. Moreover, IR data correspond well with modulated DSC endotherms located near 50 °C and 70 °C. At each transition temperature—thought to represent, respectively, a thermally driven chain conformation from planar zigzags to helices, and a dynamic disorder of helices marked by rapid gauche ? trans isomerization—the IR absorbance ratio, A₉₇₈/A₉₆₃, which represents the relative population of helical chains, undergoes an accelerated decrease. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 439–461, 2005     

Synthesis and characterization of hydrogen‐bonded thermotropic liquid crystalline aromatic‐aliphatic poly(ester–amide)s from amido diol

Fifteen highly regular hydrogen‐bonded, novel thermotropic, aromatic‐aliphatic poly(ester–amide)s (PEAs) were synthesized from aliphatic amido diols by melt polycondensation with dimethyl terephthalate and solution polycondensation with terephthaloyl chloride. Intermolecular hydrogen bonds more or less perpendicular to the main‐chain direction induce the formation and stabilization of liquid crystalline property for these PEAs. The structure of these polymers, even in the mesomorphic phase is dominated by hydrogen bonds between the amide–amide and amide–ester groups in adjacent chains. Aliphatic amido diols were synthesized by the aminolysis of γ‐butyrolactone, δ‐valerolactone and ε‐caprolactone with aliphatic diamines containing a number of methylene groups from two to six in isopropanol medium at room temperature. Effects of polarity of the solvent on solution polymerization and effect of catalyst on trans esterification were studied. These polymers were characterized by elemental analysis, FTIR, ¹H NMR, ¹³C NMR, solubility studies, inherent viscosity, DSC, X‐ray diffraction, polarized light microscopy, and TGA. All the melt/solution polycondensed PEAs showed multiple‐phase transitions on heating with second transitions identified as nematic/smectic/spherullitic texture. The mesomorphic properties were studied as a function of their chemical structure by changing alternatively m or n. Odd‐even effect on mesophase transition temperature, isotropization temperature, and crystallinity were studied. The effect of molecular weight and polydispersity on mesophase/isotropization temperature and thermal stability were investigated. It was observed that there exists a competition for crystallinity and liquid crystallinity in these PEAs © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2469–2486, 2000     

Solid‐state NMR characterizations on phase structures and molecular dynamics of poly(ethylene‐co‐vinyl acetate)

Solid‐state nuclear magnetic resonance spectroscopy and relaxation measurements, together with DSC, have been used to elucidate the structures and molecular dynamics in poly(ethylene‐co‐vinyl acetate) (EVA). It has been found that besides immobile orthorhombic and monoclinic crystalline phases, the third mobile crystalline phase (possibly the phase) of a considerable amount (36% of total crystalline phases) appears in the EVA samples, which forms during room‐temperature aging as a result of the secondary crystallization and melts at temperature somewhat higher than room temperature. Such a mobile crystalline phase has not only the well‐defined chemical shift of its own, but also has different molecular mobility from the orthorhombic phase. The mobile crystalline phase is characterized by the rapid relaxation of the longitudinal magnetization, which is caused by conventional spin‐lattice relaxation, while the slow relaxation of the longitudinal magnetization occurring in the orthorhombic phase is originated from the chain diffusion. In addition, the amorphous phase also contains two components: an interfacial amorphous phase and a melt‐like amorphous phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2864–2879, 2006     

Syntheses of polyolefin‐based stereoregular diblock copolymers for self‐assembled nanostructures

The preparation of polyolefin‐based stereoregular diblock copolymers by postpolymerization of ethenyl‐capped syndiotactic polypropylene‐based propylene/norbornene copolymer (sPP‐based P‐N copolymer) led to the successful generation of a structurally uniform stereoregular diblock copolymer for self‐assembly studies. The ethenyl‐capped prepolymer was prepared by conducting propylene/norbornene copolymerization in the presence of Me₂C(Cp)(Flu)ZrCl₂/MAO. Ozonolysis of ethenyl‐capped sPP‐based P‐N copolymer provided the formyl group end‐capped, end‐functionalized prepolymer with a quantitative functional group conversion ratio. Subsequently, connecting the formyl end‐group of the stereoregular prepolymer by coupling with living anionic polystyrene resulted in the high yield production of stereoregular diblock copolymer (sPP‐based P‐N‐block‐polystyrene), which is difficult to prepare by other methods. The resulting stereoregular diblock copolymer possesses precise chemical architecture to self‐organize into consistent nanostructures as evidenced by transmission electron microscopy and small angle X‐ray scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4843–4856, 2008     

Mechanical properties of oriented low‐density polyethylene with an oriented lamellar‐stack morphology

A quantitative study was undertaken of the anisotropy of low‐strain mechanical behavior for specially oriented polyethylene with controlled crystalline and lamellar orientation. The samples were prepared by the die drawing of injection‐molded rods of polyethylene and annealing. This produced a parallel lamellar structure for which a simple, three‐dimensional composite laminate model could be used to calculate the expected anisotropy. Experimental data, including X‐ray strain measurements of the lateral crystalline elastic constants, showed good quantitative agreement with the model prediction. The X‐ray strain measurements confirmed that the amorphous regions exert large constraints on the crystalline phase in the lateral directions, where an order of magnitude difference was found between the measured apparent lateral crystalline compliances in the lamellar‐stack sample and the expected values for a perfect crystal. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 755–764, 2000     

Main chain thermotropic liquid crystalline polyurethanes containing biphenyl mesogens based on novel AB‐type self‐polycondensation route: FT‐IR and XRD studies

The detailed mesophasic characterization of main chain liquid crystalline polyurethanes containing biphenyl mesogen, which were synthesized by the novel AB‐type self‐polycondensation approach, was carried out by using Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM), variable temperature X‐ray Diffraction (XRD), and Fourier Transform Infrared (FT‐IR) spectroscopic studies. The type of mesophase present in these polymers was identified to be the smectic A phase by POM and XRD studies. The smectic layer thickness was found to increase as the length of the spacer increased. The effect of temperature on the hydrogen bonding was analyzed by FT‐IR studies. The curve‐fitting analysis of the NH stretching and C?O stretching modes of vibrations indicated a gradual decrease in hydrogen bonding during the transition from the crystalline state to the mesophase. The mesophase to isotropic liquid transition was then accompanied by the complete disappearance of the hydrogen bonding. The biphenyl bands also showed changes during phase transitions due to the coupling of biphenyl vibration modes with the urethane linkage attached to it. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1903–1912, 2005     

Annealing induced variation of crystalline structure and mechanical properties of syndiotactic polypropylene fibers

<正>Syndiotactic polypropylene(sPP) as-spun fiber(sPP1) and drawn fiber(sPP2) were prepared by melt-spinning and melt-spinning/hot-drawing,respectively.The structure transition of the two fibers induced by annealing at different temperatures and the corresponding mechanical properties were subsequently investigated by the combination of Fourier transform infrared spectroscopy(FTIR),wide-angle X-ray diffraction(WAXD) and tensile testing.The results indicate that the chain conformation and crystal forms of the two sPP fibers are not obviously changed at low annealing temperature (40℃).With increasing the annealing temperature,the trans-planar conformation and mesophase in sPP1 and sPP2 fibers can be completely transformed to helical conformation and crystal form I under tension.Upon removing the tension,a small amount of mesophase and trans-planar conformation will be regained.The mechanical properties of the annealed fibers are manifestly dependent on their initial structure and the annealing temperature.     

Multi-Color Photoluminescence Based on Mechanically and Thermally Induced Liquid-Crystalline Phase Transitions of a Hydrogen-Bonded Benzodithiophene Derivative

Controlling assembled structures of π-conjugated liquid-crystalline molecules is of great interest in the development of stimuli-responsive luminescent materials due to their molecular motility in the ordered states. Herein, we describe a mechanoresponsive hydrogen-bonded benzodithiophene liquid-crystalline molecule that exhibits a tricolor photoluminescence switching at ambient temperature. The compound shows a shear-induced phase transition from a rectangular columnar to a metastable optically anisotropic mesophase, which is accompanied by the luminescent color change from yellow to sky-blue. The metastable mesophase exhibits a time-responsive transformation to another metastable mesophase showing a blue-green emission through isothermal aging at room temperature. The luminescent color of aged sample reverts back to the initial yellow color by thermal annealing at 150 °C. These dynamic structural changes accompanied by the emission color changes are governed by distinct π-stacking modes and hydrogen-bonded patterns. The shear-induced luminescent color change from yellow to blue is found to occur above the shear strain of 390 % at which the shear stress is 2.4×10⁵ Pa as determined from dynamic viscoelastic measurements.