Strong π-stacking causes unusually large anisotropic thermal expansion and thermochromism

Abstract

π-stacking in ground-state dimers/trimers/tetramers of N-butoxyphenyl(naphthalene)diimide (BNDI) exceeds 50 kcal ⋅ mol−1 in strength, drastically surpassing that for the *3[pyrene]2 excimer (∼30 kcal ⋅ mol−1; formal bond order = 1) and similar to other weak-to-moderate classical covalent bonds. Cooperative π-stacking in triclinic (BNDI-T) and monoclinic (BNDI-M) polymorphs effects unusually large linear thermal expansion coefficients (αa, αb, αc, β) of (452, −16.8, −154, 273) × 10−6 ⋅ K−1 and (70.1, −44.7, 163, 177) × 10−6 ⋅ K−1, respectively. BNDI-T exhibits highly reversible thermochromism over a 300-K range, manifest by color changes from orange (ambient temperature) toward red (cryogenic temperatures) or yellow (375 K), with repeated thermal cycling sustained for over at least 2 y.

Colossal Anisotropic Thermal Expansion in a Diazo‐Functionalized Compound with Switchable Solid‐State Behavior

“…[7a,9] Recently, π-stacking interactions were used to attain anisotropic TE in a naphthalenediimide-based compound. [10] Materials exhibiting unique behaviors including NTE, ZTE, large PTE, or anisotropic TE are interesting and can be utilized to construct devices. For example, anisotropic expansion in materials has successfully been used to fabricate thermomechanical devices.…”

“…However, colossal anisotropic TE has been less reported in purely organic materials, especially single‐component organic solids [7a,9] . Recently, π‐stacking interactions were used to attain anisotropic TE in a naphthalenediimide‐based compound [10] . Materials exhibiting unique behaviors including NTE, ZTE, large PTE, or anisotropic TE are interesting and can be utilized to construct devices.…”

Anomalous thermal expansion of strontium squarate trihydrate induced by hydrogen-bond weakening

“…14,15 Some uniaxial NTE compounds can be processed as preferred fibers or membranes, which can also meet practical applications. 16 Moreover, NTE can also be utilized to modify materials’ physical and chemical properties, such as luminescence, 17,18 ferroelectric, 19 nonlinear optics, 20 gas adsorption, etc . 21,22…”

“…14,15 Some uniaxial NTE compounds can be processed as preferred fibers or membranes, which can also meet practical applications. 16 Moreover, NTE can also be utilized to modify materials' physical and chemical properties, such as luminescence, 17,18 ferroelectric, 19 nonlinear optics, 20 gas adsorption, etc. 21,22 Compared with traditional inorganic NTE compounds, [23][24][25][26][27][28] the most outstanding characteristic of MOFs or coordination polymers (CPs) is their structural designability, which make them an ideal platform to realize NTE.…”

π-Stacking among the Anthracenyl Groups of a Copper Complex Resulted in Doubling of Unit Cell Volume To Provide New Polymorphs

“…However, those contribute to design catalysts and magnetic, optical, high energy materials . Aromatic π-stacking in a self-assembly influences physical properties like conductance, proton transfer, etc . Herringbone arrangement is a term used for organized π-stacks and has broad dimensions for material design .…”