Stimuli-Responsive Circularly Polarized Organic Ultralong Room Temperature Phosphorescence

Purely organic materials showing room temperature phosphorescence (RTP) and ultralong RTP (OURTP) have recently attracted much attention. However, it is challenging to integrate circularly polarized luminescence (CPL) into RTP/OURTP. Here, we show a strategy to realize CPL-active OURTP (CP-OURTP) by binding an achiral phosphor group directly to the chiral center of an ester chain. Engineering of this flexible chiral chain enables efficient chirality transfer to carbazole aggregates, resulting in strong CP-OURTP with a lifetime of over 0.6 s and dissymmetry factor of 2.3×10⁻³ after the conformation regulation upon photo-activation. The realized CP-OURTP is thus stable at room temperature but can be deactivated quickly at 50 °C to CP-RTP with high CPL stability during the photo-activation/thermal-deactivation cycles. Based on this extraordinary photo/thermal-responsive and highly reversible CP-OURTP/RTP, a CPL-featured lifetime-encrypted combinational logic device has been successfully established.     

Organic Room‐Temperature Phosphorescence with Strong Circularly Polarized Luminescence Based on Paracyclophanes

Pure organic materials with intrinsic room‐temperature phosphorescence typically rely on heavy atoms or heteroatoms. Two different strategies towards constructing organic room‐temperature phosphorescence (RTP) species based upon the through‐space charge transfer (TSCT) unit of [2.2]paracyclophane (PCP) were demonstrated. Materials with bromine atoms, PCP‐BrCz and PPCP‐BrCz, exhibit RTP lifetime of around 100 ms. Modulating the PCP core with non‐halogen‐containing electron‐withdrawing units, PCP‐TNTCz and PCP‐PyCNCz, successfully elongate the RTP lifetime to 313.59 and 528.00 ms, respectively, the afterglow of which is visible for several seconds under ambient conditions. The PCP‐TNTCz and PCP‐PyCNCz enantiomers display excellent circular polarized luminescence with dissymmetry factors as high as ?1.2×10^?2 in toluene solutions, and decent RTP lifetime of around 300 ms for PCP‐TNTCz enantiomers in crystalline state.     

Luminescent Chiral Exciplexes with Sky-Blue and Green Circularly Polarized-Thermally Activated Delayed Fluorescence

Luminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with g_lum up to 7×10⁻³, one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone (g_lum ∼7×10⁻⁴). This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge-transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor-acceptor model. Interestingly, blue, green-yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi-color CP-TADF emitters.     

New Wine in Old Bottles: Prolonging Room‐Temperature Phosphorescence of Crown Ethers by Supramolecular Interactions

Supramolecular macrocyclic hosts have long been used in smart materials. However, their triplet emission and regulation at crystal level is rarely studied. Herein, ultralong and universal room‐temperature phosphorescence (RTP) is reported for traditional crown ethers. A supramolecular strategy involving chain length adjustment and morphological locking through complexation with K⁺ was explored as a general method to tune the phosphorescence lifetime in the solid state. A maximum 10‐fold increase of lifetime after complex formation accompanied with by invisible to visible phosphorescence was achieved. A deep encryption based on this activated RTP strategy was also facilely fabricated. This work thus opens a new world for supramolecular macrocycles and their intrinsic guest responsiveness offers a new avenue for versatile smart luminescent materials.     

Helically Assembled Pyrene Arrays on an RNA Duplex That Exhibit Circularly Polarized Luminescence with Excimer Formation

Circularly polarized luminescence (CPL) was observed in pyrene zipper arrays helically arranged on an RNA duplex. Hybridization of complementary RNA strands having multiple (two to five) 2′‐O‐pyrenylmethyl modified nucleosides affords an RNA duplex with normal thermal stability. The pyrene fluorophores are assembled like a zipper in a well‐defined helical manner along the axis of RNA duplex, which, upon 350 nm UV illumination, resulted in CPL emission with pyrene excimer formation. CPL (g_lum) levels observed for the pyrene arrays in dilute aqueous solution were +2×10^?2–+3.5×10^?2, which are comparable with |g_lum| for chiral organic molecules and related systems. The positive CPL signals are consistent with a right‐handed helical structure. Temperature dependence on CPL emission indicates that the stable rigid RNA structure is responsible for the strong CPL signals. The single pyrene‐modified RNA duplex did not show any CPL signal.     

An Unexpected Chromophore–Solvent Reaction Leads to Bicomponent Aggregation‐Induced Phosphorescence

Organic luminogens with persistent room‐temperature phosphorescence (RTP) have found a wide range of applications. However, many RTP luminogens are prone to severe quenching in the crystalline state. Herein, we report a strategy to construct a donor‐sp³‐acceptor type luminogen that exhibits aggregation‐induced emission (AIE) while the donor‐sp²‐acceptor counterpart structure exhibits a non‐emissive solid state. Unexpectedly, it was discovered that a trace amount (0.01 %) of the structurally similar derivative, produced by a side reaction with the DMF solvent, could induce strong RTP with an absolute RTP yield up to 25.4 % and a lifetime of 48 ms, although the substance does not show RTP by itself. Single‐crystal XRD‐based calculations suggest that n–σ* orbital interactions as a result of structural similarity may be responsible for the strong RTP in the bicomponent system. This study provides a new insight into the design of multi‐component, solid‐state RTP materials from organic molecular systems.     

Crystal‐State Photochromism and Dual‐Mode Mechanochromism of an Organic Molecule with Fluorescence,Room‐Temperature Phosphorescence,and Delayed Fluorescence

A D‐A‐D′ type pure organic molecule, named ODFRCZ, has unique triple‐emission character covering fluorescence, phosphorescence, and delayed fluorescence (DF). The phosphorescence of ODFRCZ has a rather long lifetime of about 350 ms at room temperature. One dimer of ODFRCZ with enhanced parallel molecular packing acts more effectively to prompt ISC processes, which further generates room‐temperature phosphorescence (RTP), owing to the larger transition dipole moment and closer energy level between S₁ and T_n. ODFRCZ is a rare example of an organic RTP molecule that shows dual‐stimuli responsiveness of dual‐mode mechanochromism (fluorescence red‐shift and RTP/DF on‐off switch) and reversible crystal‐state photochromism. This work may broaden the knowledge for stimuli‐responsive RTP organic molecules and lay the foundation for their wide‐scale applications.     

Investigation on the Luminescence Performance of Four Quinolones

Abstract

In this paper we report on the low temperature phosphorescence (LTP), the low temperature fluorescence (LTF), the paper substrate room temperature phosphorescence (PS‐RTP), and the room fluorescence (RTF) properties of ciprofloxacin (CPFX), lomefloxacin (LMX), fleroxacin (FLX), and ofloxacin (OFLX), which were investigated and compared. Some rules were discovered: their maximal excitation wavelength and emission wavelength are in the range of 280–295 nm and 428–500 nm, respectively, except OFLX, and the difference in molecular structure may be responsible for it. The pH experiments show that all their emissions are strongest in acid, followed by neutral, and weakest in alkali medium. The PS‐RTP characters of lifetime and polarization were also investigated and compared. It was found that the lifetimes of PS‐RTP were all in the level of 0.1 s. These quinolones belong to long‐life phosphorescence and their PS‐RTP spectra are incompletely polarized.     

Determination of Glucose by Affinity Adsorption Solid Substrate‐room Temperature Phosphorimetry Based on Triticum Vulgare Lectin Labeled with Silicon Dioxide Nanoparticle Containing Fluorescein Isothiocyanate

In the presence of heavy atom perturber Pb2＋, silicon dioxide nanoparticle containing fluorescein isothiocyanate (FITC-SiO2) could emit a strong and stable room temperature phosphorescence (RTP) signal on the surface of acetyl cellulose membrane (ACM). It was found in the research that a quantitative specific affinity adsorption (AA) reaction between triticum vulgare lectin (WGA) labeled with luminescent nanoparticle and glucose (G) could be carried on the surface of ACM. The product (WGA-G-WGA-FITC-SiO2) of the reaction could emit a stronger RTP signal, and the ΔIp had linear correlation to the content of G. According to the facts above, a new method to determine G by affinity adsorption solid substrate room temperature phosphorimetry (AA-SS-RTP) was established, based on WGA labeled with FITC-SiO2. The detection limit (LD) of this method calculated by 3Sb/k was 0.47 pg•spot－1 (corresponding to a concentration value 1.2×10－9 g•mL－1, namely 5.3×10－9 mol•L－1), the sensitivity was high. Meanwhile, the mechanism for the determination of G by AA-SS-RTP was discussed.     

Crystal‐State Photochromism and Dual‐Mode Mechanochromism of an Organic Molecule with Fluorescence,Room‐Temperature Phosphorescence,and Delayed Fluorescence

A D‐A‐D′ type pure organic molecule, named ODFRCZ, has unique triple‐emission character covering fluorescence, phosphorescence, and delayed fluorescence (DF). The phosphorescence of ODFRCZ has a rather long lifetime of about 350 ms at room temperature. One dimer of ODFRCZ with enhanced parallel molecular packing acts more effectively to prompt ISC processes, which further generates room‐temperature phosphorescence (RTP), owing to the larger transition dipole moment and closer energy level between S₁ and T_n. ODFRCZ is a rare example of an organic RTP molecule that shows dual‐stimuli responsiveness of dual‐mode mechanochromism (fluorescence red‐shift and RTP/DF on‐off switch) and reversible crystal‐state photochromism. This work may broaden the knowledge for stimuli‐responsive RTP organic molecules and lay the foundation for their wide‐scale applications.     

Axially Chiral TADF‐Active Enantiomers Designed for Efficient Blue Circularly Polarized Electroluminescence

The use of a chiral, emitting skeleton for axially chiral enantiomers showing activity in thermally activated delayed fluorescence (TADF) with circularly polarized electroluminescence (CPEL) is proposed. A pair of chiral stable enantiomers, (?)‐(S)‐Cz‐Ax‐CN and (+)‐(R)‐Cz‐Ax‐CN, was designed and synthesized. The enantiomers, both exhibiting intramolecular π‐conjugated charge transfer (CT) and spatial CT, show TADF activities with a small singlet–triplet energy difference (ΔE_ST) of 0.029 eV and mirror‐image circularly polarized luminescence (CPL) activities with large g_lum values. Notably, CP‐OLEDs based on the enantiomers feature blue electroluminescence centered at 468 nm with external quantum efficiencies (EQEs) of 12.5 and 12.7 %, and also show intense CPEL with g_EL values of ?1.2×10^?2 and +1.4×10^?2, respectively. These are the first CP‐OLEDs based on TADF‐active enantiomers with efficient blue CPEL.     

Thermal and light control of the chiral order of azopolymers

The control of the chiroptical properties of two azopolymers, which contain chiral terminal alkyl chains, by means of thermal and light irradiation processes has been studied. Both UV–vis and CD spectra of films and dichloromethane (DCM)/hexane solutions of the polymers have been registered and analyzed before and after different irradiation conditions: 488 nm circularly polarized light (CPL) and 365 nm unpolarized light. The chiroptical properties of the polymer containing chiral 1-methylheptyloxy terminal chains depended on the thermal history of the sample. As a result, the photocontrol of the chiral response in the bulk material by CPL irradiation has been evaluated on samples cooled from the isotropic state to room temperature at different rates. The chiroptical properties of these azopolymers show an intriguing combination of control from both the supramolecular and molecular chirality level as well as the thermal history of the sample and CPL irradiation.     

Stable Enantiomers Displaying Thermally Activated Delayed Fluorescence: Efficient OLEDs with Circularly Polarized Electroluminescence

Aromatic‐imide‐based thermally activated delayed fluorescent (TADF) enantiomers, (+)‐(S,S)‐ CAI‐Cz and (?)‐(R,R)‐ CAI‐Cz , were efficiently synthesized by introducing a chiral 1,2‐diaminocyclohexane to the achiral TADF unit. The TADF enantiomers exhibited high PLQYs of up to 98 %, small ΔE_ST values of 0.06 eV, as well as obvious temperature‐dependent transient PL spectra, thus demonstrating their excellent TADF properties. Moreover, the TADF enantiomers showed mirror‐image CD and CPL activities. Notably, the CP‐OLEDs with CPEL properties based on the TADF enantiomers not only achieved high EQE values of up to 19.7 and 19.8 %, but also displayed opposite CPEL signals with g_EL values of ?1.7×10^?3 and 2.3×10^?3, which represents the first CP‐OLEDs, based on the enantiomerically pure TADF materials, having both high efficiencies and intense CPEL.     

The amplified circularly polarized luminescence emission response of chiral 1,1′‐binaphthol‐based polymers via Zn(II)‐coordination fluorescence enhancement

Two kinds of chiral 1,1′‐binaphthol (BINOL)‐based polymer enantiomers were designed and synthesized by the polymerization of 5,5′‐((2,2′‐bis (octyloxy)‐[1,1′‐binaphthalene]‐3,3′‐diyl)bis(ethyne‐2,1‐diyl))bis(2‐hydroxybenzaldehyde) ( M1 ) with alkyl diamine ( M2 ) via nucleophilic addition–elimination reaction. The resulting chiral polymers can exhibit mirror image cotton effects either in the absence or in the presence of Zn²⁺ ion. Almost no fluorescence or circularly polarized luminescence (CPL) emission could be observed for two chiral BINOL‐based polymer enantiomers in the absence of Zn²⁺. Interestingly, the chiral polymers can show strong fluorescence and CPL response signals upon the addition of Zn²⁺, which can be attributed to Zn²⁺‐coordination fluorescence enhancement effect. This work can develop a new strategy on the design of the novel CPL materials via metal‐coordination reaction. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1282–1288     

Synthesis and characterization of novel poly(vinyl chloride)‐based grafts: Poly(vinyl chloride‐co‐2‐chloropropene) fitted with multiple high‐glass‐transition‐temperature polyolefin branches

The tertiary chlorine (Cl^t) content of vinyl chloride/2‐chloropropene copolymers [P(VC‐co‐2CP)] was determined by NMR spectroscopy. Copolymers containing 6.8–47.0 Cl^t's per P(VC‐co‐2CP) chain were used to initiate the cationic grafting of α‐methylstyrene, norbornadiene, indene, and norbornene with Et₂AlCl under various conditions. Grafting was demonstrated by selective solvent extraction, and the effect of the experimental conditions on the grafting efficiency was examined. Select rheological and thermal characteristics of P(VC‐co‐2CP) grafts, including the glass‐transition temperature, heat deflection temperature, and discoloration upon heating, were studied. P(VC‐co‐2CP) carrying 7–11 poly(α‐methylstyrene) or polynorbornadiene branches per chain raised the glass‐transition temperature to, or above, that of a blend control. P(VC‐co‐2CP)s fitted with polyindene or polynorbornene branches were less effective in raising the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3644–3651, 2002     

Yellow Circularly Polarized Luminescence from C1‐Symmetrical Copper(I) Complexes

The synthesis of chiral C₁‐symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |g_lum|=1.2×10^?3. These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL‐emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.     

AIE Triggers the Circularly Polarized Luminescence of Atomically Precise Enantiomeric Copper(I) Alkynyl Clusters

Atomically precise enantiomeric metal clusters are scarce, and copper(I) alkynyl clusters with intense circularly polarized luminescence (CPL) responses have not been reported. A pair of chiral alkynyl ligands, (R/S)‐2‐diphenyl‐2‐hydroxylmethylpyrrolidine‐1‐propyne (abbreviated as R/S‐DPM ) we successfully prepared and single crystals were characterized of optically pure enantiomeric pair of atomically‐precise copper(I) clusters, [Cu₁₄(R/S‐DPM)₈](PF₆)₆ (denoted as R/S‐Cu₁₄ ), which feature bright red luminescence and CPL with a high luminescence anisotropy factor (g_lum). A dilute solution containing R/S‐Cu₁₄ was nonluminescent and CPL inactive at room temperature. Crystallization‐ and aggregation‐induced emission (CIE and AIE, respectively) contribute to the triggering of the CPL of R/S‐Cu₁₄ in the crystalline and aggregated states. Their AIE behavior and good biocompatibility indicated applications of these copper(I) clusters in cell imaging in HeLa and NG108‐15 cells.     

Reversible Photoinduced Switching of Permeability in a Cast Non‐Porous Film Comprising Azobenzene Liquid Crystalline Polymer

Permeation characteristics of an azobenzene‐containing liquid crystalline (LC) non‐porous film are investigated using a metallic corrosion method. Thin films (300 nm) are fabricated by the solution casting of an azobenzene side‐chain LC polymer on freshly polished carbon steel coupons. Coated coupons are treated under the following conditions: a) gradual annealing at a cooling rate lower than 1 °C · min⁻¹ from 150 °C (above its T_g) to room temperature, and b) irradiation at 465 nm (20 mW · cm⁻²) with either circularly polarized light (CPL) or non‐polarized light (NPL). The morphology of these films is characterized using X‐ray diffraction, polarized optical microscopy, and transmission measurements. The results suggest that the annealing treatment resulted in the formation of a polydomain structure consisting of locally ordered small smectic domains that lack mutual orientation. Ordered micro domains are surrounded by disordered phases. CPL and NPL irradiation generates a monodomain orientated structure and an isotropic liquid crystal glass, respectively. The permeability of these non‐porous films treated by CPL, NPL, and annealing are found to be 6.14 × 10⁻⁴, 1.92 × 10⁻², and 1.56 × 10⁻³ cm³ · m⁻² · d⁻¹. An orientation‐dependent structure model is constructed to explain the permeation phenomenon, considering the ordered phase is impermeable, only the disordered phase is accessible to penetrating molecules. Fast switching of gas permeation is demonstrated by alternative irradiation of the film with CPL and NPL, which results in an approximately 30‐fold difference in the permeability of the non‐porous film.

     

Self‐Stabilized Amorphous Organic Materials with Room‐Temperature Phosphorescence

The stability of pure organic room‐temperature phosphorescent (RTP) materials in air has been a research hotspot in recent years. Without crystallization or encapsulation, a new strategy was proposed to obtain self‐stabilized organic RTP materials, based on a complete ionization of a photo‐induced charge separation system. The ionization of aromatic phenol 4‐carbazolyl salicylaldehyde (CSA) formed a stable H‐bonding anion–cation radical structure and led to the completely amorphous CSA‐I film. Phosphorescent lifetimes as long as 0.14 s at room temperature and with direct exposure to air were observed. The emission intensity was also increased by 21.5‐fold. Such an amorphous RTP material reconciled the contradiction between phosphorescence stability and vapor permeability and has been successfully utilized for peroxide vapor detection.     

Cucurbit[n]urils-induced room temperature phosphorescence of quinoline derivatives

The cucurbit[7,8]urils (Q[7] and Q[8])-induced room temperature phosphorescence (RTP) of quinoline and its derivatives were firstly found in the cucurbit[n]urils chemistry. The luminophores (quinolines) and their RTP are affected by the concentration of different Q[n]s, heavy metal ions and amounts, and pH. The RTP lifetime of the luminophore has been investigated. In presence of Na₂SO₃, the cation Tl⁺ led to stronger Q[n]-induced RTP, while the RTP lifetimes of luminophore/Q[7 or 8]/KI were generally longer than that of luminophore/Q[7 or 8]/TlNO₃, the RTP lifetimes of these systems were between 0.18 and 47.4 ms. Contrary to the stable 1:2 Q[8]:guest ternary inclusion complexes at lower pHs, as suggested by ¹H NMR, electronic absorption and fluorescence spectroscopy, low Q[8]-induced room temperature phosphorescence was observed. However, at higher pHs, high intensity of cucurbit[n]urils-induced room temperature phosphorescence of these quinoline derivatives were observed, and a 1:1 Q[8]:guest inclusion complex was formed. Investigations of dependence of RTP intensity on concentration of Q[n] revealed that the highest intensity of the Q[n]-induced RTP was observed at a low mole ratio of host:guest, which is closed to 1:1. It was presumably resulted from the strong interaction of Q[n] and these guests due to the combined hydrophobic cavity interaction and the hydrophilic portal interaction of the cucurbit[n]urils with the nitrogen heterocycles guest.