Photocyclization Quantum Yield Research Articles

All-Visible-Light-Activated Diarylethene Photoswitches.

Photochromic compounds have attracted much attention for their potential applications in photo-actuators, optoelectronic devices and optical recording techniques. This interest is driven by their key photochemical and photophysical properties, which can be reversibly modulated by light irradiation. Among them, diarylethene compounds have garnered extensive investigation due to their excellent thermal stability of both open- and closed-form isomers, robust fatigue resistance, high photocyclization quantum yield and good photochromic performance in both solution and solid phases. However, a notable limitation in expanding the utility of diarylethene compounds is the necessity for ultraviolet light to induce their photochromism. This requirement poses challenges, as ultraviolet light can be detrimental to biological tissues, and its penetration is often restricted in various media. This review provides an overview of design strategies employed in the development of visible-light-responsive diarylethene compounds. These design strategies serve as a guideline for molecular design, with the potential to significantly broaden the applications of all-visible-light-activated diarylethene compounds in the realms of materials science and biomedical science.

Towards Optical Information Recording: A Robust Visible-Light-Driven Molecular Photoswitch with the Ring-Closure Reaction Yield Exceeding 96.3 .

Diarylethene molecular photoswitches hold great fascination as optical information materials due to their unique bistability and exceptional reversible photoswitching properties. Conventional diarylethenes, however, rely on UV light for ring-closure reactions, typically with modest yields. For practical application, diarylethenes driven by visible lights are preferred but achieving high ring-closure reaction yield remains a significant challenge. Herein, we synthesized a novel all-visible-light-driven photoswitch, TPAP-DTE, by facilely endcapping the dithienylethene (DTE) core with triphenylamine phenyl (TPAP) groups. Owing to the electron-donating conjugation effect of TPAP, the open-form TPAP-DTE responds strongly to short-wavelength visible lights with considerable photocyclization quantum yields and molar absorption coefficient. Upon 405 nm visible-light irradiation, TPAP-DTE achieves a ring-closure reaction yield exceeding 96.3 % (confirmed by both nuclear magnetic resonance spectroscopy and high-performance liquid chromatography). Its ring-opening reaction yield is 100 % upon irradiation with long-wavelength visible light. TPAP-DTE could be regarded as a bidirectional "quasi"-quantitative conversion molecular switch. Furthermore, TPAP-DTE exhibits robust fatigue resistance over 100 full photoswitching cycles and great anti-aging property under 85 °C and 85 % humidity for at least 1000 h. Consequently, its rewritable QR-code, multilevel data storage, and anti-counterfeiting/encryption applications are successfully demonstrated exclusively using visible lights, positioning TPAP-DTE as a highly promising medium for information recording.

Towards Optical Information Recording: A Robust Visible‐Light‐Driven Molecular Photoswitch with the Ring‐Closure Reaction Yield Exceeding 96.3 %

AbstractDiarylethene molecular photoswitches hold great fascination as optical information materials due to their unique bistability and exceptional reversible photoswitching properties. Conventional diarylethenes, however, rely on UV light for ring‐closure reactions, typically with modest yields. For practical application, diarylethenes driven by visible lights are preferred but achieving high ring‐closure reaction yield remains a significant challenge. Herein, we synthesized a novel all‐visible‐light‐driven photoswitch, TPAP−DTE, by facilely endcapping the dithienylethene (DTE) core with triphenylamine phenyl (TPAP) groups. Owing to the electron‐donating conjugation effect of TPAP, the open‐form TPAP−DTE responds strongly to short‐wavelength visible lights with considerable photocyclization quantum yields and molar absorption coefficient. Upon 405 nm visible‐light irradiation, TPAP−DTE achieves a ring‐closure reaction yield exceeding 96.3 % (confirmed by both nuclear magnetic resonance spectroscopy and high‐performance liquid chromatography). Its ring‐opening reaction yield is 100 % upon irradiation with long‐wavelength visible light. TPAP−DTE could be regarded as a bidirectional “quasi”‐quantitative conversion molecular switch. Furthermore, TPAP−DTE exhibits robust fatigue resistance over 100 full photoswitching cycles and great anti‐aging property under 85 °C and 85 % humidity for at least 1000 h. Consequently, its rewritable QR‐code, multilevel data storage, and anti‐counterfeiting/encryption applications are successfully demonstrated exclusively using visible lights, positioning TPAP−DTE as a highly promising medium for information recording.

Circularly polarized luminescence switch based on a photochromic europium(III) helicate derived coordination polymer

Chiroptical switches based on circularly polarized luminescence (CPL) have shown the promising applications in advanced information technologies. Herein, a pair of lanthanide coordination polymer enantiomers [Eu2(LR)3(BTFPO)2]n and [Eu2(LS)3(BTFPO)2]n with light-regulated CPL property are designed, which are assembled by a chiral binuclear triple-stranded Eu3+ helicates [Eu2(LR/S)3] coordinated with two photochromic triphenylphosphine oxides (BTFPO). Upon the alternative UV and 526 nm light irradiation, the complexes show the reversible photochromism, PL and CPL responses. Notably, the luminescence dissymmetry factor, glum of 5D0→7F1 (591 nm) transition shows an obvious increase from 0.19 to 0.29 before and after 275 nm light irradiation. Additionally, the emission from Eu3+ center is not completely quenched in closed-ring state due to the low photocyclization (Фo-c) quantum yield of the polymer. The partial maintenance of emissive intensity is of essential importance for the monitor of CPL signal. More importantly, the CPL photo-switching property of the complexes in solid hybrid film is maintained, and still displays the enhanced CPL emission in photostationary state. Further, the potential applications of the doping film in logic gate and anti-counterfeiting were investigated.

Tuning the photochemical ring-closing reaction efficiency in diarylethene-based photoswitches through engineering of internal charge transfer.

The photochemical quantum yield is one of the key features for a photoswitch and its tuning is challenging. In an attempt to tackle this issue within the popular diarylethene-based switches, we have explored the potential to use internal charge transfer (CT), a readily controllable parameter, for an effective modulation of the photocyclization quantum yield. For this, a homogeneous family of terarylenes, a sub-class of diarylethenes, with different CT characters, but the same photochromic core was designed and its photochromic properties were fully investigated. A clear correlation was found between the cyclization quantum yield and the CT character of the switch. More precisely, almost linear relationships were established between the ring-closing quantum yield and (i) the electron density variation accompanying the S0 → S1 transition and (ii) the percentage of LUMO on the reactive carbon atoms. Such a correlation was rationalized by a joint spectroscopic analysis and theoretical modelling of both ground and first excited states, introducing the concept of "early" or "late" photochromes. Encouragingly, such a potentally predictive model also seemed relevant when applied to some other diarylethene-based switches reported in the literature.

Nondestructive All-Optical Readout through Photoswitching of Intramolecular Excimer Emission.

We report the first intramolecular excimer photoswitching induced by molecular motion within a dithienylethene (DTE) molecule without destructive readout. The photochromic compound DTE bears two pyrene chromophores, judiciously positioned to face each other in the DTE's open form. The close proximity of the pyrenes in the open form is confirmed by NMR experiments and geometry optimization. Intense pyrene excimer luminescence is recorded, upon both one- and two-photon excitation (OPE and TPE). The photocyclization reaction of the DTE core induces a molecular motion of one pyrene moiety which thus prevents the possibility of formation of an excimer. Our DTE-based pyrene is stable upon TPE irradiation and shows a high photocyclization quantum yield. Such property specifications allow us to report the original nondestructive readout fluorescence by alternating exposure to OPE and TPE.

Sterically Hindered Diarylethenes with a Benzobis(thiadiazole) Bridge: Enantiospecific Transformation and Reversible Photosuperstructures.

ConspectusPhotochromic diarylethenes featuring reversible regulation by external light irradiation have attracted increasing attention in versatile applications such as logic gates, supramolecular systems, liquid crystals, and super-resolution imaging because of their outstanding bistability and fatigue resistance. However, for typical diarylethene systems, there always exist three typical unsolved issues. The first is how to modulate the bistability between the open and closed forms from the viewpoint of ethene bridge aromaticity. The second is how to decrease and avoid the photoinactive parallel conformer in order to achieve a high quantum yield, since the open form possesses the photoactive antiparallel (ap) conformation and the photoinactive parallel (p) conformation. Because of the typical rapid rotation of the flexible side aryl groups, the two conformers cannot be separated efficiently, thereby resulting in a relatively low photocyclization quantum yield. The third is how to fulfill the enantiospecific transformation with reversibility to photomodulate the chirality. Stereochemically, the ap conformer with C2 symmetry can be further subdivided into a pair of enantiomers with P and M helicity originating from the central hexatriene moiety. Similarly, the rapid rotation can also lead to the loss of intrinsic chirality, restricting the development and application of light-driven chiroptical switches. Accordingly, it is desirable to construct a specific diarylethene system to break through these bottlenecks for real versatile applications.Our group has recently developed a unique sterically hindered diarylethene system based on benzobis(thiadiazole) as the ethene bridge for completely solving these issues. We introduce a low-aromaticity benzobis(thiadiazole) unit into the diarylethene as a central ethene bridge with incomparably high bistability. To block or freeze the rotation of flexible side aryls, we further incorporate a large bulky benzothiophene unit to induce a large steric hindrance, or rotation barrier, between the ethene bridge and side aryls, thereby successfully separating multiple conformers of the diarylethenes with high photocyclization quantum yields and enantiospecific photoreaction. Consequently, given such a fantastic building block, we enhance its performance by means of supramolecular self-assembly, thereby realizing unique conformer-dependent self-assembly as well as unprecedented concerted isomerization and enantiospecific photoreaction of photoresponsive metallacycles. In addition, decoration of the intrinsically chiral diarylethenes with mesogenic units can enable us to manipulate the helical superstructure of liquid crystals, thus achieving a multiple anticounterfeiting technique and a quadridimensional manipulable laser. We also unravel the dual aggregation-induced emission (AIE) behavior of the sterically hindered diarylethene, especially as applied in super-resolution imaging.

Boosting Visible Light-induced Photocyclization Quantum Yield of a Diarylethene-perylenebisimide Dyad by Introducing a Ketone Spacer Group

Abstract Recently, we found a unique visible light-induced photocyclization reaction in a diarylethene-perylenebisimide dyad based on multiplicity conversion via intramolecular energy transfer. Here we report on the remarkable enhancement of photocyclization quantum yield under visible light irradiation by changing the spacer unit from an ester to a ketone group. This simple modification lifts the restrictions of solvent choice and oxygen quenching.

Cover Feature: Tetrathienyl Corannulene Compounds with Highly Sensitive Photochromism (Chem. Eur. J. 49/2022)

Tetrathienyl corannulene compounds showed highly sensitive photochromism with a large molar absorption coefficient and photocyclization quantum yield close to 1, although dithienyl phenanthrene compounds showed no photoreactivity. Such a high photoreactivity was rationalized by the predominance of the photoreactive atropisomers amplified by energy migration, and the curvature-induced short distance between photoreactive carbons. More information can be found in the Research Article by M. Yamada, T. Kawai, and co-workers (DOI: 10.1002/chem.202201286).

Efficient blue light-responsed dithienylethenes with exceptional photochromic performance

Three novel dithienylethenes modified by bifluoroboron β-diketonate fragments have been successfully developed. Upon blue light irradiation, they reached photostationary state within 2–5 s, as well as 100% conversion ratio and photocyclization quantum yield of > 0.70. Such fascinating photochromism were endowed by collaborative role of electron-withdrawing effect of BF2bdk group to reduce HOMO-LUMO electronic gap for the open isomer, together with intramolecular hydrogen bonds and CH-π interactions favoring antiparallel conformation fixation. Moreover, they displayed specific discrimination and photoswitchable bacterial imaging for S. aureus.

Light-Triggered Metal Coordination Dynamics in Photoswitchable Dithienylethene-Ferrocene System.

The C2-symmetric photochromic molecule 3, containing dithienylethene (DTE) and ferrocene units connected by an alkyne bridge, represents a unique probe where a metal (Hg2+) binds with the central DTE moiety. Both photoisomerized states of 3 (open, 3o; closed, 3c) are found to interact with Hg2+ ion by the S atoms of the DTE core; however, the binding constants (from a UV-vis study) and DFT calculations suggest that the open isomer (3o) binds with the metal ion more strongly than that of the closed isomer (3c). Notably, the course of metal binding does not perturb the inherent photoisomerization properties of the DTE core and the photoswitchability persists even in the metal-coordinated form of 3, however, with a comparatively slower rate. The quantum yields for photocyclization (Φo→c) and photocycloreversion (Φc→o) in the free form are 0.56 and 0.007, respectively, whereas the photocyclization quantum yield in the Hg2+ complexed species is 0.068, 8.2 times lower than the photocyclization quantum yield (Φo→c) of free 3o. Thus, the rate of photoisomerization can be modulated by a suitable metal coordination to the DTE core. The dynamics of photoswitchability in the metal-coordinated form of DTE has been explored by experimental means (UV-vis and electrochemical studies) as well as quantum chemical calculations.

Modeling Photonastic Materials: A First Computational Study.

Photonastic materials present a directional and repeatable deformation of the material shape due to transduction from light energy to mechanical energy. Among these materials, light-responsive polymers, composed of photochromic molecules embedded in a polymer matrix, are of high interest. The present work aims at laying the foundation stone of the modeling of the photomechanical behavior of such systems by proposing a computational strategy that is able to investigate (i) the impact of the polymer matrix on the photochromic properties of a dithienylethene (DTE) switch and (ii) the impact of the photochromic reaction on the polymer environment. Contrary to previous approaches, the present model is able to propose a realistic arrangement of the photochrome embedded in the polymer film, thanks to the adaptation of the so-called "controlled-like polymerization algorithm" [Lemarchand, C. A.; J. Chem. Phys. 2019, 50, 224902]. Our strategy relies on molecular dynamics (MD) simulations and time-dependent density functional theory (DFT) calculations. Careful analysis of MD trajectories and comparison with simulations in solution have shown the rigidification of the DTE molecule due to the presence of the polymer chains, which hindered the interconversion between the DTE open-form isomers and can probably modify the photocyclization quantum yield. Besides, the UV-vis absorption properties of the DTE open-form isomers are more impacted by the polymer embedding than its closed-form counterpart. Concerning the impact of the photoreaction on the polymer matrix, the time evolution of the pressure tensor and of the atomic displacements in the matrix have shown that (i) the cyclization reaction has a negligible impact; (ii) the cycloreversion reaction induces a locally large and anisotropic pressure increase and leads to a collective displacement of the polymer matrix away from the reactive center; and (iii) the characteristic time scale associated with these coupled processes is below 1 ps. Therefore, the two processes involved in photonastic motions, namely, the photoreaction and the relaxation of the polymer matrix after the photoswitch structural change, cannot be decoupled.

Metal-directed synthesis of quadruple-stranded helical Eu(III) molecular switch: a significant improvement in photocyclization quantum yield.

The self-assembly of a quadruple-stranded Eu(iii) helicate induces the conformation transformation of a DAE-based photochromic ligand from parallel to antiparallel, which brings a significant improvement in the photocyclization quantum yield (Φo-c) as compared with the free ligand. Furthermore, the photocontrolled open- and closed-rings of the ligand realized a reversible modulation toward Eu3+ center emission.

Photochromic Performance of 5-Heteroaryl-4-vinyl-2-phenylthiazole Derivatives

Abstract Compounds 5-(5-methyl-2-phenyl-4-thiazolyl)-4-(5-methyl-1-phenyl-1-propenyl)-2-phenylthiazole 1a and 5-(2-methyl-5-phenyl-3-thienyl)-4-(2-methyl-1-phenyl-1-propenyl)-2-phenylthiazole 2a having an S-N heteroatom-contact interaction and a CH-N hydrogen bonding were synthesized in an attempt to obtain new photochromic compounds having terarylene and 1-aryl-2-vinylcyclopentene backbones. The S-N interaction and CH-N hydrogen bonding of 1a and 2a can be explained by DFT calculation and temperature dependent 1H NMR spectra. The tethering interactions are expected to stabilize the reactive conformation of 1a and 2a, and to increase the photocyclization quantum yield. Two 5-heteroaryl-4-vinyl-2-phenylthiazoles 1 and 2 underwent reversible photocyclization reactions from the open-ring isomers 1a and 2a to the closed-ring isomers 1b and 2b, respectively. The photocyclization quantum yields of 1a and 2a are 0.57 and 0.63, which are 3 times larger than that of 1-thiazolyl-2-vinylcyclopentene derivatives (0.20). The number of photochromic cycles exhibited by 1b was 50 in the presence of air, which is higher than that of 2b.

A Visible-Near-Infrared Light-Responsive Host-Guest Pair with Nanomolar Affinity in Water.

The discovery of stimuli-responsive high affinity host-guest pairs with potential applications under biologically relevant conditions is a challenging goal. This work reports a high-affinity 1:1 complex formed between cucurbit[8]uril and a water-soluble photochromic diarylethene derivative. It was found that, by confining the open isomer within the cavity of the receptor, a redshift in the absorption spectrum and an enhancement of the photocyclization quantum yield from Φ=0.04 to Φ=0.32 were induced. This improvement in the photochemical performance enables quantitative photocyclization with visible light that, together with the near-infrared light-induced ring-opening reaction and the 100-fold selectivity for the closed isomer, confirms this as an outstanding light-responsive affinity pair.

Adjustable Photochromic Behavior of a Diarylethene-Based Bistable [3]Rotaxane.

An acid-base stimulus-responsive diarylethene-based bistable [3]rotaxane has been constructed through a threading-stoppering method, manifesting a reversible shuttling motion undergoing acid-base stimulation. In this system, two macrocycles can be driven to unfasten or restrict the photoswitchable framework by addition of the appropriate acid or base, revealing that photocyclization quantum yield of the [3]rotaxane in the "Near" state is superior to that in the "Far" state. These findings offer a new approach for directional improvement of photochromic performance and construction of molecular machine with a shuttling motion.

Diastereoselective photocyclization of a photochromic diarylethene having a benzo[b]phosphole P-oxide group

A photochromic diarylethene derivative 1 having a chiral benzo[b]phosphole P-oxide at the aryl moiety underwent a diastereoselective photocyclization reaction in acetonitrile upon irradiation with ultraviolet (UV) light. It was found that the diastereomeric excess (d.e.) value changes depending on the conversion ratio from the open- to closed-ring isomer as well as the irradiation wavelength. This is attributed to the difference in the photocycloreversion quantum yields of diastereomers of the closed-ring isomer. The diarylethene showed a high photocyclization quantum yield owing to a high population of photoreactive conformers of the open-ring isomer by the steric effect of the benzo[b]phosphole P-oxide group.

Photo- and acid induced multicolor switches based on pyridine-containing perfluorodiarylethene derivatives

Two novel perfluorodiarylethenes which contains a 2-methylbenzo[b]furane and a modified pyridine moiety were synthesized. Such structure may induce F⋯N or S⋯N heteroatom contact which was newly observed. Experiments results showed that the photocyclization quantum yield exhibited a strong correlation with the two weak intramolecular interactions, which behaved solvent independency. Moreover, both novel pyridine-perfluorodiarylethenes exhibited an obvious acidichromism, and the absorption maxima of their closed-ring isomers showed a prominent bathochromic shift to the near-infrared region.

Tunable photochromism in the robust dithienylethene-containing phospholes: design, synthesis, characterization, electrochemistry, photophysics, and photochromic studies.

A series of dithienylethene-containing phosphole derivatives has been designed, synthesized and characterized. One of the compounds has been characterized by X-ray crystallography. Upon photoexcitation, the compounds exhibit drastic color changes, ascribed to the reversible photochromic behavior. Their photochromic, photophysical and electrochemical properties have been studied. They show photochromic reactivities with high photocyclization quantum yields. Their photophysical and photochromic properties are found to be facilely tuned in this system by substitution at the phosphole backbone, as well as variation on the extent of π-conjugation of the phosphole backbone. Some selected compounds have been demonstrated to exhibit photochromic properties in polymethylmethacrylate (PMMA) films.

Separation of Photoactive Conformers Based on Hindered Diarylethenes: Efficient Modulation in Photocyclization Quantum Yields

AbstractEndowing both solvent independency and excellent thermal bistability, the benzobis(thiadiazole)‐bridged diarylethene system provides an efficient approach to realize extremely high photocyclization quantum yields (Φo‐c, up to 90.6 %) by both separating completely pure anti‐parallel conformer and suppressing intramolecular charge transfer (ICT).