Sensitivity and Resolution Development of Spiropyran‐based Molecular Photoswitches

The phenylazo moiety and its donor‐ and acceptor‐substituted derivatives are studied as effective auxochromes to improve their sensitivity and resolution for distinguishing between the spiro (SP; OFF) and mero (ON) forms in molecular photoswitching applications. Thus, 13 azospiropyran derivatives were synthesized and their spectroscopic and photokinetic behaviors were studied. The quality of photochromic reactions of the synthesized photochromic compounds were compared using a dose–response model. Interestingly, by replacing the nitro group in 6‐nitrospiropyran (ε = 0.42 × 10⁴ M^?1 cm^?1) with a simple phenylazo moiety, the SP form is still colorless and the color intensity of the merocyanine (MC) form is improved desirably by extending the conjugation length ( 1a , ε = 1.35 × 10⁴ M^?1 cm^?1). The presence of a hydrophilic OH group or a CH₃ group at the para position of phenylazo moiety revealed more or less the same photochromic properties as 1a . The OCH₃ group substituted at position 6 of the phenylazo moiety at the para position of the azobenzene moiety effectively increased the photochromic properties with the maximum k‐value for SP to MC switching. Meanwhile, Cl, Br, COOH, and NO₂ groups at the para position of the azobenzene moiety revealed the reduction in photochromic properties compared to 1a .     

Synthesis,crystal structure and photochromic property of a phenethyl viologen bismuth(III) chloride

Viologen bismuthate halides generally show photochromic properties. In the present work, phenylethyl alcohol was introduced into chloro bismuthates in the hope to prepare photochromic crystalline materials and finally a photochromic inorganic-organic hybrid, (PeV)₃(Bi₂Cl₉)₂ (1), based on an in situ generated PeV²⁺ cation (PeV²⁺ = phenethylviologen = N,N′-diphenethyl-4,4′-bipyridinium), has been obtained, whose microstructure contains a discrete dimer [Bi₂Cl₉]^3– counterion identified by single crystal X-ray diffraction. More importantly, 1 exhibits a typical photochromic behavior, which can be mainly attributed to the reversible inter-conversion between the monocation viologen radical [PeV]^+? and the viologen dication [PeV]²⁺.     

A fourfold interpenetrating cadmium(II) metal–organic framework based on 2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine with reversible photochromic properties

2,4,6‐Tris(pyridin‐4‐yl)‐1,3,5‐triazine (tpt), as an organic molecule with an electron‐deficient nature, has attracted considerable interest because of its photoinduced electron transfer from neutral organic molecules to form stable anionic radicals. This makes it an excellent candidate as an organic linker in the construction of photochromic complexes. Such a photochromic three‐dimensional (3D) metal–organic framework (MOF) has been prepared using this ligand. Crystallization of tpt with Cd(NO₃)₂·4H₂O in an N,N‐dimethylacetamide–methanol mixed‐solvent system under solvothermal conditions afforded the 3D MOF poly[[bis(nitrato‐κ²O,O′)cadmium(II)]‐μ₃‐2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine‐κ³N²:N⁴:N⁶], [Cd(NO₃)₂(C₁₈H₁₂N₆)]_n, which was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and single‐crystal X‐ray diffraction. The X‐ray diffraction crystal structure analysis reveals that the asymmetric unit contains one independent Cd^II cation, one tpt ligand and two coordinated NO₃^? anions. The Cd^II cations are connected by tpt ligands to generate a 3D framework. The single framework leaves voids that are filled by mutual interpenetration of three independent equivalent frameworks in a fourfold interpenetrating architecture. The compound shows a good thermal stability and exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron‐transfer generation of radicals in the tpt ligand.     

A two‐dimensional CdII coordination polymer based on naphthalenediimide: synthesis,crystal structure and photochromic properties

Naphthalenediimides, a class of organic dyes with an expanded π‐electron‐deficient plane, have attracted considerable interest because of their photoinduced electron transfer from neutral organic moieties to stable anionic radicals. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic two‐dimensional coordination polymer has been prepared using N,N′‐bis(pyridin‐4‐ylmethyl)naphthalene‐1,8:4,5‐bis(dicarboximide) (DPMNI). In crystallization tubes, upon slow diffusion of an MeOH solution of cadmium perchlorate into a CHCl₃ solution of DPMNI, the complex poly[[bis[μ₂‐2,7‐bis(pyridin‐4‐ylmethyl)benzo[imn][3,8]phenanthroline‐1,3,6,8(2H,7H)‐tetrone‐κ²N:N′]bis(perchlorato‐κO)cadmium(II)] chloroform tetrasolvate], {[Cd(C₂₆H₁₆N₄O₄)₂(ClO₄)₂]·4CHCl₃}_n, (I), was obtained. The asymmetric unit contains one Cd²⁺ cation, two DPMNI ligands, two coordinated ClO₄⁻ anions and four CHCl₃ solvent molecules. Each Cd²⁺ cation is interconnected by four DPMNI linkers to generate a neutral two‐dimensional naphthalenediimide coordination network with all the ClO₄⁻ anions above or below this plane. Strong interlaminar anion–π interactions between the coordinated ClO₄⁻ anions and the imide rings of an adjacent layer lead to a three‐dimensional supramolecular structure. Compound (I) exhibits reversible photochromic behaviour and photocontrolled tunable luminescence properties, which may originate from the photoinduced electron‐transfer generation of radicals in the DPMNI ligand.     

Control of the Single‐Molecule Magnet Behavior of Lanthanide‐Diarylethene Photochromic Assemblies by Irradiation with Light

Lanthanide‐based extended coordination frameworks showing photocontrolled single‐molecule magnet (SMM) behavior were prepared by combining highly anisotropic Dy^III and Ho^III ions with the carboxylato‐functionalized photochromic molecule 1,2‐bis(5‐carboxyl‐2‐methyl‐3‐thienyl)perfluorocyclopentene (H₂dae), which acts as a bridging ligand. As a result, two new compounds of the general formula [{Ln^III₂(dae)₃(DMSO)₃(MeOH)} ? 10 M eOH]_n (M=Dy for 1 a and Ho for 2 ) and two additional pseudo‐polymorphs [{Dy^III₂(dae)₃(DMSO)₃(H₂O)} ? x MeOH]_n ( 1 b ) and [{Dy^III₂(dae)₃(DMSO)₃(DMSO)} ? x MeOH]_n ( 1 c ) were obtained. All four compounds have 2D coordination‐layer topologies, in which carboxylate‐bridged Ln₂ units are linked together by dae^2? anions into grid‐like frameworks. All four compounds exhibited a strong reversible photochromic response to UV/Vis light. Moreover, both 1 a and 2 show field‐induced SMM behavior. The slow magnetic relaxation of 1 a is influenced by the photoisomerization reaction leading to the observation of the cross‐effect: photocontrolled SMM behavior.     

Synthesis and characterization of a photochromic magnesium(II) coordination polymer based on a naphthalene diimide ligand

Naphthalene diimides, which are planar, chemically robust and redox‐active, are an attractive class of electron‐deficient dyes, which can undergo a single reversible one‐electron reduction to form stable radical anions in the presence of electron donors upon irradiation. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic one‐dimensional linear coordination polymer has been prepared using N ,N ′‐bis(3‐carboxyphenyl)naphthalene‐1,8:4,5‐tetracarboximide (H₂BBNDI). Crystallization of H₂BBNDI with magnesium nitrate in an N ,N ′‐dimethylformamide (DMF)/ethanol/H₂O mixed‐solvent system under solvothermal conditions afforded the one‐dimensional coordination polymer catena‐poly[[bis(dimethylformamide‐κO )magnesium(II)]‐bis[μ‐N‐(3‐carboxylatophenyl)‐N ′‐(3‐carboxylphenyl)naphthalene‐1,8:4,5‐tetracarboximide‐κ²O :O ′]], [Mg(C₂₈H₁₃N₂O₈)₂(C₃H₇NO)₂]_n . The asymmetric unit contains half of a magnesium cation, one HBBNDI⁻ ligand and one DMF molecule. Two partially deprotonated HBBNDI⁻ ligands bridge two magnesium cations to form a one‐dimensional chain. Strong inter‐chain π–π interactions between the naphthalene rings of the HBBNDI⁻ ligand and the imide rings of adjacent chains provide a two‐dimensional structure. The supramolecular three‐dimensional framework is stabilized by π–π interactions between naphthalene rings of neighbouring two‐dimensional supramolecular networks. The complex exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron‐transfer generation of radicals in the HBBNDI⁻ ligand.     

Synthesis,structure, and properties of the [RuNO(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>][Co(CN)<Subscript>6</Subscript>] complex containing a photochromic cation

The salt of cobalt hexacyanide with the photochromic mononitrosyl cation [RuNO(NH₃)₅]³⁺ with the composition [RuNO(NH₃)₅][Co(CN)₆] was synthesized. Single crystals of the salt were grown, and the crystal structure was solved. The photochromic properties were studied by differential scanning calorimetry (DSC). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 545–548, March, 2008.     

Untersuchung reversibler Photoprozesse durch Blitzlichtphotolyse IV. Triplettzustände des 1, 3, 6′, 8′- tetramethyl-dehydrodianthrons

By means of the flash photolysis technique, transient absorption spectra attributed to tetramethyl-dehydrodianthrone (TMD) in both the photochromic and triplet states have been investigated in polymethylmethacrylate matrices and in the solvent triacetin. In polymethylmethacrylate matrices and in rigid glasses of triacetin the triplet state of TMD is heavily populated. Triplet-triplet absorption and phosphorescence measurements show that below 180°K the triplet decay follows first order kinetics with the decay constant k=11,3 ± 0,1 s^?1. In incompletely solidified triacetin glass it is possible to monitor the transient absorption of the photochromic and the triplet state simultaneously. It is shown that the photochromic state ¹A₁* is not generated via the triplet state. Therefore the authors suggest a kinetic scheme characterised by a direct singlet state - photochromic state transition.     

Structural characterization and photochromic behaviour of a novel compound based on a π‐acidic naphthalene diimide derivative and a double hydroxide‐bridged dinuclear AlIII aqua ion cluster

Noncovalent interactions, such as π–π stacking interactions, C—H…π interactions and hydrogen bonding, are important driving forces for self‐assembly in the construction of functional supermolecules and materials, especially in multicomponent supramolecular systems. Herein, a novel compound based on a π‐acidic naphthalene diimide derivative and a double hydroxide‐bridged dinuclear Al³⁺ aqua ion cluster, namely bis[N,N′‐bis(2‐sulfonatoethyl)‐1,4,5,8‐naphthalene diimide] di‐μ‐hydroxido‐bis[tetraaquaaluminium(III)] tetrahydrate, (C₁₈H₁₂N₂O₁₀S₂)₂[Al₂(OH)₂(H₂O)₈]·4H₂O, was obtained using the above‐mentioned common noncovalent interactions, as well as uncommon lone‐pair–π interactions. Functional molecular modules were connected by these noncovalent interactions to generate obvious photochromic properties. The compound was prepared by the self‐assembly of N,N′‐bis(2‐sulfoethyl)‐1,4,5,8‐naphthalene diimide and Al(NO₃)₃·9H₂O under mixed solvothermal conditions, and was characterized in detail by single‐crystal X‐ray diffraction, powder X‐ray diffraction and FT–IR spectroscopy. The thermal stability and photochromic properties were also investigated; furthermore, in‐situ solid‐state UV–Vis absorption spectroscopy and electron spin resonance (ESR) were used to clarify the photochromic mechanism.     

含硝基一代光致变色液晶树枝状大分子的光化学研究

研究了树外围含12个硝基偶氮苯基元新型一代碳硅烷光致变色液晶树枝状大分子G1和基元小分子M1在溶液中的最大吸收波长、摩尔消光系数、反-顺光化学异构化反应速率常数、热回复异构化反应速率常数、光化学回复异构化反应平衡常数及速率常数. G1的光致变色反应速率常数的数量级为10^－1 s^－1, 而含偶氮基元液晶聚硅氧烷的光致变色反应速率常数的数量级为10^－8 s^－1, 因此液晶树枝状大分子的光响应速率比后者快10⁷倍. G1的光回复异构化反应平衡常数k_t /k_c为1.76～1.77, 有作为光控开关材料的应用前景.     

Structure and photochromic and magnetic properties of 1-isopropyl-3,3,5′,6′-tetramethylspiro[indoline-2,2′-2<Emphasis Type="Italic">H</Emphasis>-pyrano[3,2-<Emphasis Type="Italic">b</Emphasis>]pyridinium] tris(oxalato)chromate(III)

Single crystals of 1-isopropyl-3,3,5′,6′-tetramethylspiro[indoline-2,2′-2H-pyrano[3,2-b]-pyridinium] tris(oxalato)chromate(III) (Sp)₃Cr(C₂O₄)₃ were prepared for the first time. The molecular and crystal structure of this salt was studied by X-ray diffraction. The crystal structure of the salt consists of the structural units [3(Sp)⁺…Cr(C₂O₄)₃ ³⁻], in which the charged pyranopyridinium moieties of the photochromic cations (Sp)+ are directed toward the oxalate groups, whereas the indoline moieties are directed into the cavities between the structural units. This structure appeared to be favorable for photochromic transformations in the crystals. Under UV irradiation of the (Sp)₃Cr(C₂O₄)₃ salt, the thermally stable closed form of spiropyran (λ_max = 370 nm) is transformed into the open form (λ_max = 574 and 603 nm). The reverse cyclization proceeds slowly in the dark (k = 1.0(2)·10⁻⁵ s⁻¹ and rapidly under visible light irradiation. The spectroscopic and photochromic properties of the oxalatochromate (Sp)₃Cr(C₂O₄)₃ are similar to those of the iodide SpI. The magnetic properties of (Sp)₃Cr(C₂O₄)₃ were studied before and after UV irradiation.     

Novel Aspects of a Convenient Synthesis and of Electroproperties of Derivatives Based on Diphenylamine

The substituted monomers 4a , c , d, 5a , b, 6a, 7a , b , and 8a of novel poly(diphenylamines), possessing the respective photochromic groups, were synthesized by the Stille cross‐coupling methodology (Scheme). The hyperbranched structures were characterized by ¹H‐ and ¹³C‐NMR spectroscopy. The obtained monomers show good stability in common organic solvents such as CHCl₃, toluene, and CH₂Cl₂, and exhibit excellent thermal stability. Electrochemical results and theoretical calculations suggest that oxidation and reduction of the monomers start from the side of the amine function and the five‐membered heterocyclic ring moieties, respectively.     

三代碳硅烷光致变色液晶树状物的光化学研究——端基含108个4-丁氧基偶氮苯介晶基元

报道了新化合物含108个丁氧基偶氮基元端基的三代(D3)碳硅烷光致变色液晶树状物在各溶液中的反-顺光异构化(光致变色)反应速率常数k_p, 光化学回复异构化正/逆反应速率常数k_t和k_c, 热回复异构化反应速率常数k_H, 光化学回复异构化反应平衡常数k_t/k_c, 活化能E, 异构化转换率及热回复异构化反应中的反-顺异构体组分比. D3的光致变色反应速率常数为10^－1 s^－1, 而含偶氮基元的光致变色液晶聚硅氧烷的光致变色反应速率常数为10^－8 s^－1, 因此, D3的光响应速度比后者快10⁷倍.     

Synthesis and exploring the excited-state PES of photochromic hydrogen bond-assembled [2]rotaxane based on 1,3-Diazabicyclo-[3.1.0]hex-3-enes

Here, the synthesis of photochromic hydrogen bond-assembled [2]rotaxanes using bis-fumarate as a thread for the first time is reported. In fact, photochromic 1,3-diazabicyclo[3.1.0]hex-3-ene moieties were used as stoppers and two-atom spacers managed good binding sites for the tetralactam macrocycles in clipping reactions. Moreover, the yields of photochromic [2]rotaxanes highly depended on the NO₂ substituent stoppers. While the thread with a para –NO₂ substituent as stopper units was shown to be an excellent template for the synthesis of photochromic [2]rotaxanes. The structures of the [2]rotaxanes are established clearly in solution by chemical shifts of the ¹H ¹³C NMR signals and UV–Vis spectra. A pronounced bathochromic shift was occurred in the excitation wavelength of photochoromic [2]rotaxanes compared with the absorption band of photochromic threads. Therefore, these organizations can be applied in light-driven molecular switches and motors. The reversible transformation of trans and cis geometric photoisomers under UV radiation was identified. In other efforts, the possibility of the process of trans to cis interconversion of the fumarate linker under UV irradiation has been examined computationally and it has appeared that it may cause the transverse of the bis-fumarate linker inside the tetralactam macrocycle to some extent.

     

Zn2+ doped ormosil–phosphotungstate hybrid films with enhanced photochromic response

Owing to the wide use of photochromic materials in UV sensors and dosimeters, considerable efforts have been made to increase the UV-response and sensitivity of the existing classes of photochromic materials. In this study, we report a simple sol–gel route for the preparation of highly photochromic transparent films based on ormosil–phosphotungstate hybrid materials. The effect of addition of Zn²⁺ ions on the photochromic response of these hybrid films and the possible mechanism involved is discussed. Compared to the undoped samples, the photochromic response of the Zn²⁺-doped hybrid films increases by 59–237 % depending on the concentration of Zn²⁺ ions added to the sol formulation. No structural or electronic change in the phosphotungstate dye was observed by vibrational spectroscopy or UV spectroscopy, though micro X-ray fluorescence (μ-XRF) analysis showed that the addition of Zn²⁺ in the sol–gel preparations leads to an increase in the amount of phosphotungstate (HPW) incorporated in the dip-coated films. Furthermore, TEM and nano-energy-dispersive X-ray showed formation of nano-agglomerates consisting of Zn and HPW in the Zn²⁺-doped samples. Zn K-edge X-ray absorption near edge structure analysis also confirmed the formation of the salt H_x[Zn(OH₂)₆] _2?xPW₁₂O₄₀. It is suggested that these Zn-phosphotungstate nano-agglomerates get trapped into the ormosil network during films preparation leading to increased concentration of the phosphotungstate anions in the films, in accordance with results from μ-XRF analysis. Raman spectroscopy confirmed that the Keggin structure of HPW is preserved in the hybrid films. FTIR spectra of the matrix part of the samples are identical before and after UV-irradiation, which suggests that the photochromic process does not involve oxidation of the organic functionalities. These highly photochromic hybrid films are promising candidates for the design of practical UV-sensing devices and dosimeters.     

Four Polyoxometalate-Viologen Discoloration Materials for UV Probing,Inkless and Erasable Printing and Visual Detection of Hg2+

In this work, four POM-based compounds containing viologen ligands were synthesized, namely {Cu^II(tybipy)₂(DMF)₂[H₂(β-Mo₈O₂₆)]₂} ⋅ 4 C₂H₇N ( 1 ), (Htybipy)₂ ⋅ (β-Mo₈O₂₆) ( 2 ) (tybipy⋅Br=1-Thiophen-3-ylmethyl-[4,4’]bipyridinyl-1-ium bromide), [Cu^II(nibipy)₂(4,4’-bipy)] ⋅ (SiW₁₂O₄₀) ( 3 ), (Hnibipy)₂ ⋅ (δ-Mo₈O₂₆) ( 4 ) (nibipy⋅Cl=1-(4-Nitro-benzyl)-[4,4’]bipyridinyl-1-ium chloride, 4,4’-bipy=4,4’-bipyridine). In compounds 1 and 3 , Cu²⁺ and mixed organic ligands modify POM anions. On the other hand, 2 and 4 are supramolecular structures only containing ligands and anions. Under Xe lamp with filter (300-400 nm) irradiation, these four compounds showed good photoresponse and photochromic ability, which can be used in mixed matrix films for visible UV detectors. Compounds 1 – 4 also have photoluminescence property and show good fluorescence quenching effect. A suspension of four compounds can be evenly spread on filter paper as inkless and erasable printing materials. Compounds 1 and 2 were also used as Hg²⁺ fluorescence detectors. The fluorescence intensity of 1 decreased by ca. 90 % when the concentration of Hg²⁺ increased to 40 mM. Moreover, we also prepared composites 1 / 2 @Hg²⁺, 1 @Cu²⁺, 1 @Co²⁺ by introducing 1 / 2 and Hg²⁺, Cu²⁺ and Co²⁺ to detection paper respectively, which can act as photochromic materials with features of fast color recovery.     

Photochromic Coatings Containing Ag(Cl1−xBrx) Microcrystals

Photochromic ormosil coatings containing Ag(Cl_1–x Br _x ) microcrystals were formed on a glass substrate via the sol-gel process. Methyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane were used as starting materials of the ormosil matrices. 3-chloropropyltrimethoxysilane and bromophenyltrimethoxysilane were added as halogen sources and silver colloidal dispersion was introduced into the precursor sol. The coated glass became transparent and photosensitive after Ag(Cl_1–x Br _x ) microcrystals were precipitated in the coatings above 300°C. Insertion of a SiO₂ buffer layer between the substrate and photochromic layer was effective in preventing Ag⁺ migration into the substrate. Photochromic performances were improved by the substitution of Cl with Br and the incorporation of a minute amount of Cu.     

Photochromic transformations in solutions of 8,8′-diquinolyl disulfide and di(mercaptoquinolinato)nickel(<Emphasis Type="SmallCaps">II</Emphasis>)

The nature of intermediate species and their reactions were studied by laser pulse photolysis for a photochromic system consisting of 8,8′-diquinolyl disulfide (RSSR) and a planar Ni^II complex di(mercaptoquinolinato)nickel(II) (Ni(SR)₂) in toluene and benzene solutions. Under exposure to laser radiation, disulfide RSSR dissociates to two RS^· radicals, whose spectrum has an intense absorption band with a maximum at λ = 400 nm (ε = 8400 L mol⁻¹ cm⁻¹). The radicals disappear by recombination (2k _rec = 4.6 · 10⁹ L mol⁻¹ s⁻¹). In the presence of the Ni(SR)₂ complex, coordination of the radical (k _coord = 4.4 · 10⁹ L mol⁻¹ s⁻¹) competes with recombination to form a radical complex RS^· Ni(SR)₂ having an intense absorption band with a maximum at 460 nm (ε = 16 600 L mol⁻¹ cm⁻¹). This species decays in the second-order reaction (2k = 4.6 · 10⁴ L mol⁻¹ s⁻¹). Since the photochromic system returns to the initial state, the reaction of two radical complexes is assumed to produce radical recombination and reduction of the disulfide and Ni(SR)₂ complex. Analysis of the kinetic data showed that some RS^· radicals decay in the microsecond time interval due to the reaction with the RS^· Ni(SR)₂ radical complex (k = 3.1 · 10⁹ L mol⁻¹ s⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2291–2300, October, 2005.     

An organic photochromic compound: (2S)‐2′‐ethoxy‐1,3,3‐trimethyl‐6′‐(piperidin‐1‐yl)spiro[indoline‐2,3′‐3′H‐naphtho[2,1‐b][1,4]oxazine]

In the course of our synthesis of hybrid photochromic compounds, the unexpected new organic photochromic title compound, C₂₉H₃₃N₃O₂, (I), was obtained. It is a derivative of the parent spirooxazine 1,3,3‐trimethyl‐6′‐(piperidin‐1‐yl)spiro[indoline‐2,3′‐3′H‐naphtho[2,1‐b][1,4]oxazine], (II). The 2′‐ethoxy group gives (I) different photochromic properties from its parent spirooxazine (II).     

Photochromic Dithienylethene‐Containing Triarylborane Derivatives: Facile Approach to Modulate Photochromic Properties with Multi‐addressable Functions

A series of dithienylethene‐containing triarylboranes has been designed, synthesized, and characterized. The electrochemistry, photophysics, and photochromic behavior have also been studied. The photophysical and photochromic properties could be facilely tuned in this system by varying the thiophene spacers (thiophene, thienothiophene, and bithiophene) between the dithienylethene and the dimesitylboron (BMes₂) or the position of the BMes₂ substitution in the thiophene spacers. The absorption of closed form has been found to be more sensitive towards the structural modification upon incorporation of the BMes₂ unit. Moreover, multi‐addressable photochromic reactivity is obtained upon addition of Lewis base (F^?), which is due to the formation of boron–Lewis base adduct. The dependence of the photophysical and photochromic properties on the thiophene spacers and the position of the BMes₂ substitution has been further supported by computational studies.