Gyroscopes and the Chemical Literature, 2002–2020: Approaches to a Nascent Family of Molecular Devices

Molecular Dynamics of Steroidal Rotors Probed by Theoretical, Spectroscopic and Dielectric Methods

Our study focuses on molecular rotors with fast-moving rotators and their potential applications in the development of new amphidynamic crystals. Steroidal molecular rotors with a dipolar fluorine-substituted phenyl group as the rotator were synthesized and characterized. Three different rotors were investigated with varying numbers of fluorine atoms. A comprehensive analysis was performed using vibrational spectroscopy (Raman, FT-IR), electronic circular dichroism (ECD), and dielectric response to understand the behavior of the investigated model rotors. The results were supported by theoretical calculations using Density Functional Theory (DFT) methods. The angle-dependent polarized Raman spectra confirmed the crystallinity of the samples. Nearly frequency and temperature-independent permittivity suggest low-frequency librational motion of stators. An in-depth analysis of ECD spectra revealed high conformational flexibility in solution, resulting in low ECD effects, while in the solid-state with restricted rotation, significant ECD effects were observed. These findings shed light on the conformational behavior and potential applications of the studied steroidal molecular rotors.

Supramolecular Logic Gates Based on the Conjugates of Calixarenes and Carbohydrates

In the era of application-oriented research, laboratory to real life translation is highly regarded and in great demand. This could mean that molecular science developed for sensing and detecting a variety of chemical species awaits conversion to devices. In that, the molecular logic gates are the most promising ones where the information storage and/or data processing can be easily carried out in terms of molecular inputs and electrical response outputs. This would facilitate the simultaneous execution of a diverse array of molecular sensing functions. The recent progress in molecular logic gates based on supramolecular optical receptors, in particular, fluorescent ones, such as calixarene derivatives and carbohydrate conjugates will have a transformative impact on molecular devices and will encourage this science to yield technology. Therefore, this review provides a critical evaluation of recent publications on molecular logic gates based on the derivatives of calixarenes and glyco-conjugates, including several from our own research group, with the view that the corresponding applications are a beneficiary in laboratory-to-device translation. In addition, this review is also expected to assist young researchers in planning their research focus in the broad area of supramolecular-based logic gates targeting some specific applications.

Macrocyclic Sulfur Ligand Stabilized Trans-Palladium Dichloride Complex: Syntheses, Structure, Chlorine Rotation, and Application in α-Olefination of Nitriles by Primary Alcohols

Herein, we have reported the synthesis of a macrocyclic organosulfur ligand (L1) having a seventeen-membered macrocyclic ring. Subsequently, the corresponding trans-palladium complex (C1) of bulky macrocyclic organosulfur ligand (L1) was synthesized by reacting it with PdCl2 (CH3 CN)2 salt. The newly synthesized ligand and complex were characterized using various analytical and spectroscopic techniques. The complex showed a square planar geometry with trans orientation of two ligands around the palladium center. The complex possesses intramolecular SCH…Cl interactions of 2.648 Å between the macrocyclic ligand and palladium dichloride. The potential energy surface (PES) for the rotational process of C1 suggested a barrier of ~23.81 kcal/mol for chlorine rotation. Furthermore, the bulky macrocyclic organosulfur ligand stabilized palladium complex (C1) was used as a catalyst (2.5 mol %) for α-olefination of nitriles by primary alcohols. The α,β-unsaturated nitrile compounds were found to be the major product of the reaction (57-78 % yield) with broad substrate scope and large functional group tolerance. Notably, the saturated nitrile product was not observed during the reaction. The mechanistic studies suggested the formation of H2 and H2 O as only by-products of the reaction, thereby making the protocol greener and sustainable.

Molecular rotators anchored on a rod-like anionic coordination polymer adhered by charge-assisted hydrogen bonds

On the basis of variable-temperature single-crystal X-ray diffraction, variable-temperature/frequency dielectric analysis, variable-temperature solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations, here we present a new model of crystalline supramolecular rotor (i-PrNHMe2)[CdBr3], where a conformationally flexible near-spherical (i-PrNHMe2)+ cation functions as a rotator and a rod-like anionic coordination polymer {[CdBr3]-}∞ acts as the stator, and the adhesion of them is realized by charge-assisted hydrogen bonds.

Giant Crystalline Molecular Rotors that Operate in the Solid State

Molecular motion in the solid state is typically precluded by the highly dense environment, and only molecules with a limited range of sizes show such dynamics. Here, we demonstrate the solid-state rotational motion of two giant molecules, i.e., triptycene and pentiptycene, by encapsulating a bulky N-heterocyclic carbene (NHC) Au(I) complex in the crystalline media. To date, triptycene is the largest molecule (surface area: 245 Å2 ; volume: 219 Å3 ) for which rotation has been reported in the solid state, with the largest rotational diameter among reported solid-state molecular rotors (9.5 Å). However, the pentiptycene rotator that is the subject of this study (surface area: 392 Å2 ; volume: 361 Å3 ; rotational diameter: 13.0 Å) surpasses this record. Single-crystal X-ray diffraction analyses of both the developed rotors revealed that these possess sufficient free volume around the rotator. The molecular motion in the solid state was confirmed using variable-temperature solid-state 2 H spin-echo NMR studies. The triptycene rotor exhibited three-fold rotation, while temperature-dependent changes of the rotational angle were observed for the pentiptycene rotor.

Sequential self-assembly of calix[4]resorcinarene-based heterobimetallic Cd8Pt8 nano-Saturn complexes

A rational molecular design strategy is introduced for selective metal-ligand coordination, enabling the quantitative self-assembly of heterobimetallic nano-Saturn complexes. During the sequential multicomponent self-assembly, the CdII ions and organometallic trans-PtII motifs demonstrate preferential binding to specific ligands. The pre-designed directive interactions allow for precise control over the structural characteristics.

Trityl-Based Lanthanide-Supramolecular Assemblies Exhibiting Slow Magnetic Relaxation

The triphenylmethane (trityl) group has been recognized as a supramolecular synthon in crystal engineering, molecular machine rotors and stereochemical chirality inductors in materials science. Herein we demonstrate for the first time how it can be utilized in the domain of molecular magnetic materials through shaping of single molecule magnet (SMM) properties within the lanthanide complexes in tandem with other non-covalent interactions. Trityl-appended mono- (HL1 ) and bis-compartmental (HL2 ) hydrazone ligands were synthesized and complexated with Dy(III) and Er(III) triflate and nitrate salts to generate four monometallic (1-4) and two bimetallic (5, 6) complexes. The static and dynamic magnetic properties of 1-6 were investigated, revealing that only ligand HL1 induces assemblies (1-4) capable of showing SMM behaviour, with Dy(III) congeners (1, 2) able to exhibit the phenomenon also under zero field conditions. Theoretical ab initio studies helped in determination of Dy(III) energetic levels, magnetic anisotropic axes and corroborated magnetic relaxation mechanisms to be a combination of Raman and quantum tunnelling in zero dc field, the latter being cancelled in the optimum non-zero dc field. Our work represents the first study of magneto-structural correlations within the trityl Ln-SMMs, leading to generation of slowly relaxing zero-field dysprosium complexes within the hydrogen-bonded assemblies.

Rapid Access to Encapsulated Molecular Rotors via Coordination-Driven Macrocycle Formation

Macrocycle formation that relies upon trans metal coordination of appropriately placed pyridine ligands within an arylene ethynylene construct provides rapid and reliable access to molecular rotators encapsulated within macrocyclic stators. Showing no significant close contacts to the central rotators, X-ray crystallography of AgI -coordinated macrocycles provides plausibility for unobstructed rotation or wobbling of rotators within the central cavity. Solid-state 13 C NMR of PdII -coordinated macrocycles supports the notion of unobstructed movement of simple arenes in the crystal lattice. Solution 1 H NMR studies indicate complete and immediate macrocycle formation upon the introduction of PdII to the pyridyl-based ligand at room temperature. Moreover, the formed macrocycle is stable in solution; a lack of significant changes in the 1 H NMR spectrum upon cooling to -50 °C is consistent with the absence of dynamic behavior. The synthetic route to these macrocycles is expedient and modular, providing access to rather complex constructs in four simple steps involving Sonogashira coupling and deprotection reactions.

Coordination-Driven Tetragonal Prismatic Cage and the Investigation on Host-Guest Complexation

A coordination-driven host has been reported to encapsulate guests by noncovalent interactions. Herein, we present the design and synthesis of a new type of prism combining porphyrin and terpyridine moieties with a long cavity. The prism host can contain bisite or monosite guests through axial coordination binding of porphyrin and aromatic π interactions of terpyridine. The ligands and prismatic complexes were characterized by electrospray ionization mass spectrometry (ESI-MS), TWIM-MS, NMR spectrometry, and single-crystal X-ray diffraction analysis. The guest encapsulation was investigated through ESI-MS, NMR spectrometry, and transient absorption spectroscopy analysis. The binding constant and stability were determined by UV-Vis spectrometry and gradient tandem MS (gMS²) techniques. Based on the prism, a selectively confined condensation reaction was also performed and detected by NMR spectrometry. This study provides a new type of porphyrin- and terpyridine-based host that could be used for the detection of pyridyl- and amine-contained molecules and confined catalysis.

Structures and Supramolecular Properties of Inclusion Complexes of Anthracene-Triptycene Nanocages with Fullerene Guests and Their Dynamic Motion as Molecular Gyroscopes

Three derivatives of macrocyclic cage compounds consisting of diarylanthracene and triptycene units were synthesized. These nanocages formed host-guest complexes with C₆₀ and other fullerene guests as confirmed by ¹ H NMR and fluorescence spectroscopy. The association constant of the mesityl and 2,4,6-tributoxyphenyl derivatives with C₆₀ was determined to be 2.2 × 10⁴  L mol^-1 , which was larger than that of the pentafluorophenyl derivative. Direct experimental evidence of the complexation was obtained by X-ray diffraction analysis: the guest C₆₀ molecule was included in the cavity via multipoint CH⋅⋅⋅π interactions. Dynamic disorders of the included C₆₀ molecule in variable-temperature X-ray analysis indicated uniaxial motion, such as gyroscopic motion. The unique dynamic behavior of the spherical C₆₀ rotor anchored by the cage stator via CH⋅⋅⋅π interactions in the crystal, as well as substituent effects on the association properties, are discussed with the aid of DFT calculations.

Syntheses, homeomorphic and configurational isomerizations, and structures of macrocyclic aliphatic dibridgehead diphosphines; molecules that turn themselves inside out

The diphosphine complexes cis- or trans-[upper bond 1 start]PtCl₂(P((CH₂) _n )₃P[upper bond 1 end]) (n = b/12, c/14, d/16, e/18) are demetalated by MC[triple bond, length as m-dash]X nucleophiles to give the title compounds (P((CH₂) _n )₃)P (3b-e, 91-71%). These "empty cages" react with PdCl₂ or PtCl₂ sources to afford trans-[upper bond 1 start]MCl₂(P((CH₂) _n )₃P[upper bond 1 end]). Low temperature ³¹P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in,in (major) and out,out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: ΔH ^‡ 7.3/8.2 kcal mol^-1, ΔS ^‡ -19.4/-11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60-51) : (40-49) mixtures of (in,in/out,out) : in,out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH₃. The configurational stabilities of in,out-3b, c, e preclude phosphorus inversion in the interconversion of in,in and out,out isomers. Low temperature ³¹P NMR spectra of in,out-3b, c reveal degenerate in,out/out,in homeomorphic isomerizations (ΔG ^‡ _Tc 12.1, 8.5 kcal mol^-1). When (in,in/out,out)-3b, c, e are crystallized, out,out isomers are obtained, despite the preference for in,in isomers in solution. The lattice structures are analyzed, and the D ₃ symmetry of out,out-3c enables a particularly favorable packing motif. Similarly, (in,in/out,out)-3c, e·2BH₃ crystallize in out,out conformations, the former with a cycloalkane solvent guest inside.

Square-Planar and Octahedral Gyroscope-Like Metal Complexes Consisting of Dipolar Rotators Encased in Dibridgehead Di(triaryl)phosphine Stators: Syntheses, Structures, Dynamic Properties, and Reactivity

For a variety of purposes, it is of interest to embed metals in cagelike trans-spanning di(triaryl)phosphine ligands. Toward this end, a combination of P(p-C₆H₄O(CH₂)_mCH═CH₂)₃ [3; m = 4 (a), 5 (b), 6 (c), and 7 (d)], [Rh(COD)(μ-Cl)]₂, and CO gives square-planar trans-Rh(CO)(Cl)[P(p-C₆H₄O(CH₂)_mCH═CH₂)₃]₂ (4a-4d). Reactions of 4b-4d with Grubbs' catalyst (first generation) and then H₂ (catalyst PtO₂) yield the title compounds trans-Rh(CO)(Cl)[P(p-C₆H₄O(CH₂)_nO-p-C₆H₄)₃P] (n = 2m + 2, 6b-6d; 26-41% from 4b-4d). Two are crystallographically characterized. The Cl-Rh-CO moieties rapidly rotate on the NMR time scale at -120 °C, per the ample clearance provided by the (CH₂)_n segments. Steric interactions with the PC₆H₄O linkages are analyzed. LiC≡CAr displaces the chloride ligand from 6b to give RhC≡CAr adducts (Ar = C₆H₅/p-C₆H₄CH₃, 7b/8b). The ArC≡C-Rh-CO rotator of 7b rapidly rotates on the NMR time scale (-70 °C), but with 8b, the longer p-CH₃C₆H₄C≡C group is confined between two (CH₂)₁₂ bridges, even at 120 °C. Reactions of Re(CO)₅(X) and 3c (140 °C) give octahedral mer,trans-Re(CO)₃(X)[P(p-C₆H₄O(CH₂)₆CH═CH₂)₃]₂ (X = Cl/Br), and metathesis/hydrogenation sequences yield mer,trans-Re(CO)₃(X)[P(p-C₆H₄O(CH₂)₁₄O-p-C₆H₄)₃P]. Reactions of 6c and 6d and excess PMe₃ give the free diphosphines P(p-C₆H₄O(CH₂)_nO-p-C₆H₄)₃P (14c and 14d, 83-75%). The addition of 14d to [Rh(CO)₂(μ-Cl)]₂ reconstitutes 6d (87%). Both in,in and out,out isomers of 14c and 14d are possible, but low-temperature NMR spectra show one set of signals, consistent with rapid homeomorphic isomerizations that turn the molecules inside out. Thermolyses (C₆D₅Br, 140 °C) effect phosphorus inversion to give in,out isomers.

Design of rotational potential in a phenyltriptycene molecular rotor by exploiting CH/π-interaction between tripticil hydrogen and phenyl

The chemistry of artificial molecular rotors has recently attracted considerable attention in the field of molecular machines. Phenyltriptycene could be used as a stepwise molecular rotor because it is composed of a phenyl rotor and a triptycene stator, in which the rotational potential can be designed by introducing substituents. In this study, a novel design of the relative energies among three rotamers of a substituted phenyltriptycene by exploiting the CH/π-interaction between a peri-hydrogen and phenyl was investigated. First, the structures of two different phenyltriptycenes were compared to confirm CH/π-interactions. Second, the effects of the substituents of 1,4,5-trichloro-3',5'-dimethoxyphenyltriptycene on the relative energies were investigated by structural analysis, temperature-dependent nuclear magnetic resonance studies, and density functional theory calculations. The obtained results should facilitate the design of novel molecular switches and/or molecular rotors.

Structures and Oxidation Properties of Phenylene-Bridged Diazacycloalkanes: Ring Size Effects on Structures and Properties

Phenylenediamine derivatives have been investigated as functional molecules because of their characteristic oxidation properties. In this study, phenylene-bridged diazacycloalkanes, that is, C10, C12, and C14, in which numbers indicate the lengths of a side chain, were synthesized, and the effects of the macroring size on their structures and oxidation properties were investigated. X-ray crystallography revealed that the structures around the nitrogen atoms were remarkably dependent on the chain lengths. The benzene plane of C10 is arranged almost perpendicular to the macroring to avoid steric contact. However, the benzene plane of C14 and alkyl frame were co-planar. Stabilization resulting from conjugation was comparable to destabilization caused by macroring strain according to DFT calculations. Structural differences between C10 and C14 caused changes in the NMR chemical shifts of the inner methylene protons and first oxidation potentials in solution. Notably, the properties of C12 can be analyzed as those of distributed structures, which is of interest with respect to exploiting the metastable structure of the molecules. The observed relationships between the steric structures and properties can facilitate the design of functional molecules containing phenylenediamine moieties.

A surprise landing on the terra incognita of macrocyclic dibridgehead diorganoarsines: syntheses, structures, and reactivities

Reactions of trans-[Fe(CO)₂(NO)(As((CH₂)_n)₃As)]⁺ BF₄^- (n = 10, 12, 14) and Bu₄N⁺ Cl^- afford the title compounds As((CH₂)_n)₃As, which upon reaction (n = 14) with MCl₂ (M = Pt, Ni), Rh(CO)(Cl), and Fe(CO)₃ sources reconstitute cage like complexes trans-ML_n(As((CH₂)₁₄)₃As). Reactions with H₂O₂ and BH₃ give the corresponding arsine oxides and boranes. Crystal structures of metal-free species reveal out,out isomers, but cage complex formation is proposed to entail homeomorphic isomerization to in,in isomers with endo directed lone pairs.

Insights into the Molecular Dynamics of Quasi-Spherical (Chloromethyl)triethylammonium Confined in a Weakly Bound Ionic Cocrystal

Here, we report a weakly bound ionic cocrystal, (Et₃NCH₂Cl)₂[ZnCl₄], which undergoes a reversible structural phase transition owing to the switched molecular dynamics of the quasi-spherical (Et₃NCH₂Cl)⁺ cation from static to dynamic. Interestingly, a unique rolling and moving mechanism is uncovered for such a cation in the high-temperature phase, where its two methylene groups exhibit different kinetic energy barriers. This study provides a meaningful insight into the solid-state molecular dynamics of large-size quasi-spherical molecules that contain both a rigid core and flexible shell.

Synthesis and rotational dynamics of diazamacrocycles having bridged 1,4-naphthylene as framed molecular rotors

1,4-Naphthylene bridged diazamacrocycles were synthesized and characterized as novel framed molecular rotors, and dependence of the rotation on the frame size was investigated.

Bulky selenium ligand stabilized trans-palladium dichloride complexes as catalyst for silver-free decarboxylative coupling of coumarin-3-carboxylic acids

This report describes synthesis of three new trans -palladium dichloride complexes of bulky selenium ligands. These complexes possess a Cl-Pd-Cl rotor spoke attached to a Se-Pd-Se axle. The new ligands and palladium complexes ( C1 - C3 ) were characterized with the help of NMR, HRMS, UV-Vis., IR, and elemental analysis. The single crystal structure of metal complex C2 confirmed a square planer geometry of complex with trans -orientation. The X-ray structure revealed intramolecular secondary interactions (SeCH---Cl) between chlorine of PdCl 2 and CH 2 proton of selenium ligand. Variable temperature NMR data shows coalescence of diastereotopic protons, which indicates pyramidal inversion of selenium atom at elevated temperature. The relaxed potential energy scan of C2 suggests a rotational barrier of ~12.5 kcal/mol for rotation of chlorine atom through Cl-Pd-Cl rotor. The complex C3 possess dual intramolecular secondary interactions (OCH 2 ---Cl and SeCH 2 ---Cl) with stator ligand. Molecular rotor C2 was found to be most efficient catalyst for the decarboxylative Heck-coupling under mild reaction conditions. The protocol is applicable to a broad range of substrates with large functional group tolerance and low catalyst loading (2.5 mol %). The mechanism of decarboxylative Heck-coupling reaction was investigated through experimental and computational studies. Importantly the reaction works under silver-free conditions which reduces the cost of overall protocol. Further, the catalyst also worked for decarboxylative arylation and decarboxylative Suzuki-Miyaura coupling reactions with good yields of the coupled products.

Platinum(II) alkyl complexes of chelating dibridgehead diphosphines P((CH2)n)3P (n = 14, 18, 22); facile cis/trans isomerizations interconverting gyroscope and parachute like adducts

The gyroscope like dichloride complexes trans-Pt(Cl)₂(P((CH₂)_n)₃P) (trans-2; n = c, 14; e, 18; g, 22) and MeLi (2 equiv.) react to yield the parachute like dimethyl complexes cis-Pt(Me)₂(P((CH₂)_n)₃P) (cis-4c,e,g, 70-91%). HCl (1 equiv.) and cis-4c react to give cis-Pt(Cl)(Me)(P((CH₂)₁₄)₃P) (cis-5c, 83%), which upon stirring with silica gel or crystallization affords trans-5c (89%). Similar reactions of HCl and cis-4e,g give cis/trans-5e,g mixtures that upon stirring with silica gel yield trans-5e,g. A parallel sequence with trans-2c/EtLi gives cis-Pt(Et)₂(P((CH₂)₁₄)₃P) (cis-6c, 85%) but subsequent reaction with HCl affords trans-Pt(Cl)(Et)(P((CH₂)₁₄)₃P) (trans-7c, 45%) directly. When previously reported cis-Pt(Ph)₂(P((CH₂)₁₄)₃P) is treated with HCl (1 equiv.), cis- and trans-Pt(Cl)(Ph)(P((CH₂)₁₄)₃P) are isolated (44%, 29%), with the former converting to the latter at 100 °C. Reactions of trans-5c and LiBr or NaI afford the halide complexes trans-Pt(X)(Me)(P((CH₂)₁₄)₃P) (trans-9c, 88%; trans-10c, 87%). Thermolyses and DFT calculations that include acyclic model compounds establish trans > cis stabilities for all except the dialkyl complexes, for which energies can be closely spaced. The σ donor strengths of the non-phosphine ligands are assigned key roles in the trends. The crystal structures of cis-4c, trans-5c, trans-7c, and trans-10c are determined and analyzed together with the computed structures.

Simultaneous synthesis and characterization of in/out-isomers of disilabicyclo[14.14.14]alkanes

Facile and simultaneous synthesis of diphenyl-disilabicyclo[14.14.14]alkane in/out-isomers was achieved by using organosilicon chemistry. Although the formation of several in/out-isomers would be conceivable, only two diastereomers, i.e. the (traditional-)out,out-isomer and the twist-out,out-isomer, could be isolated because of homeomorphic isomerization. Crystal structures of the diastereomers were confirmed.

Toward Frameworks with Multiple Aligned and Interactive Fe(CO)3 Rotators: Syntheses and Structures of Diiron Complexes Linked by Two trans-Diaxial α,ω-Diphosphine Ligands Ar2P(CH2)nPAr2

Reactions of (η⁴-benzylideneacetone)Fe(CO)₃ and the α,ω-diphosphines Ar₂P(CH₂)_nPAr₂ afford the trigonal bipyramidal diiron tetraphosphorus complexes trans,trans-(CO)₃Fe[Ar₂P(CH₂)_nPAr₂]₂Fe(CO)₃ (n/Ar = 3/Ph 3, 4/Ph 4a, 4/p-tol 4b; 56-19%). Crystal structures establish essentially parallel P-Fe-P axes, iron-iron distances of 5.894(9)-5.782(1) Å (3) and 6.403(1)-6.466(1) Å (4a,b), and van der Waals radii of 4.45 Å for the Fe(CO)₃ rotators, the planes of which are offset by 0.029-1.665 Å. Analogous reactions of Ph₂P(CH₂)₆PPh₂ yield the square pyramidal monoiron complex trans-(CO)₃Fe[Ph₂P(CH₂)₆PPh₂] (6', 31%), a rare case where a diphosphine spans trans basal positions (∠P-Fe-P 147.4(2)°). Both 3 and 6' exhibit two CO ¹³C NMR signals at room temperature, indicating slow exchange on the NMR time scale, which in the former could entail Fe(CO)₃/Fe(CO)₃ gearing. Under analogous conditions, 4a,b exhibit one signal. Previously reported adducts of Fe(CO)₃ and Ph₂P(CH₂)_nPPh₂ are surveyed (1:1, n = 1-5; 2:2, n = 5), and the IR ν_C≡O band patterns and energies of all complexes analyzed with the aid of DFT calculations. The diiron complexes are preferred thermodynamically. Attention is given to limiting types of Fe(CO)₃/Fe(CO)₃ interactions in the diiron complexes.

Steric effects on the intramolecular charge transfer fluorescence of benzo[b]thiophene-1,1-dioxide bridged macrocages

Intramolecular charge transfer (ICT) fluorescence has been widely investigated and exploited in sensor molecules. However, steric effects on the ICT fluorescence properties have rarely been reported so far, although research in this area would promote an understanding of the basics of solvation. Herein, we report the detailed fluorescence properties of bis(trimethylsilyl)benzo[b]thiophene-1,1-dioxide (TMSBTO2) and its caged cyclophanes and non-cage isomers, which demonstrate ICT fluorescence in various solutions. The fluorescence band maxima for these benzo[b]thiophene-1,1-dioxides (BTO2s) showed a red-shift with increasing solvent polarity, confirming ICT fluorescence characteristics. The linearity of the Lippert-Mataga plots was confirmed for all ICT fluorescence measured in hexane, toluene, AcOEt, CH2Cl2, and EtOH. The slopes of the plots decreased in the following order: TMSBTO2, non-cage isomers, and caged BTO2s. It is concluded that the Onsager radii for these BTO2s were increased in the abovementioned order, assuming that the difference in the dipole moments between the excited and ground states for these BTO2s was identical.