Substituent Correlations Characterized by Hammett Constants in the Spiropyran–Merocyanine Transition

Brügner, Oliver; Reichenbach, Thomas; Sommer, Michael; Walter, Michael

doi:10.1021/acs.jpca.7b01248

Cited by 30 publications

(26 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…More rigorously, the reduction potentials were evaluated by using the Hammett equation to identify a linear free energy relationship between 2‐substituent on the imidazolium and the Hammett substituent constant . This approach has been successful for a broad array of studies including fulleroid electrochemistry, rates of benzylic radical dimerization, and photochromic spiropyran isomerization . The imidazolium bromide and triflate reduction half‐wave potentials were plotted against both meta and para Hammett substituent constants, and linear fits were applied, as shown in Figure .…”

Section: Resultsmentioning

confidence: 94%

“…[41,42] This approach has been successful for a broad array of studies including fulleroid electrochemistry, [43] rates of benzylic radical dimerization, [44] and photochromic spiropyran isomerization. [45] The imidazolium bromide and triflate reduction half-wave potentials were plotted against both meta and para Hammett substituent constants, and linear fits were applied, as shown in Figure 2. Note that only the most linear relationships are shown in Figure 2, and the comparison of linear fits can be seen in Figure S12a-b.…”

Section: Electrochemistrymentioning

confidence: 99%

See 1 more Smart Citation

Synthesis and electrochemical evaluation of 2‐substituted imidazolium salts

Hogan

Sutherland

2017

J of Physical Organic Chem

View full text Add to dashboard Cite

Herein, we report the synthesis, electrochemical, and computational evaluation of six 2‐substituted imidazolium bromides and six 2‐substituted imidazolium triflates. All final compounds were obtained in 2 or fewer synthetic steps from inexpensive starting materials and display a single, irreversible electrochemical reduction. The reduction potentials span a range greater than 1 V depending on the electron withdrawing power of the 2‐substituent. Imidazolium bromides such as Bn2(H)ImBr reduce with E1/2 = −2.70 V vs Fc/Fc+, whereas the electron‐withdrawing Br‐containing analog Bn2(Br)ImBr reduces at only −1.58 V vs Fc/Fc+. The reduction potential of imidazolium bromides obeys a linear free energy relationship to σm Hammett constants, whereas imidazolium triflates correlate better with the σp Hammett constants. These results indicate that the stabilizing effect of the 2‐substituent is anion‐sensitive, changing from induction to resonance upon exchanging bromide for triflate. Predicted electron affinities from density functional theory–optimized structures of imidazolium cations and reduced species more closely match experimental data for the triflates, suggesting that a triflate anion does not electronically perturb the imidazolium core as much as a bromide. Taken together, these data highlight the dual modularity of imidazolium salts by changing both 2‐substituent and anion.

show abstract

Section: Resultsmentioning

confidence: 94%

Section: Electrochemistrymentioning

confidence: 99%

Synthesis and electrochemical evaluation of 2‐substituted imidazolium salts

Hogan

Sutherland

2017

J of Physical Organic Chem

View full text Add to dashboard Cite

show abstract

“…[11,13,14,16,17] Notably,a lmost all of these systems use 6-nitro-SP derivatives.The nitro group lowers the energy of the corresponding MC form and hence facilitates SP!MC isomerization. [18] Thep reviously reported mainchain alternating para,para-SP copolymers did not show…”

mentioning

confidence: 99%

“…After fractionation, this material showed at oughness close to that of aromatic polycarbonates (E = 1GPa, e = 122 %). [18] Thep reviously reported mainchain alternating para,para-SP copolymers did not show Subsequently,S chlüter et al investigated various kinked polyarylenes,w ith some of them exhibiting toughness at high molecular weight after fractionation.…”

mentioning

confidence: 99%

“…Fort he first time,c opolymers with p,p-SPBr 2 were mechanochromic under positive strain. [18] In order to be able to observe mechanochromism regardless,the high strength of PmmpPof up to 50 MPa at yield is probably key (see Supporting Information). Figure 1shows that repeated switching was possible 25 times.T his is am arked difference compared to SP-based mechanochromic systems reported so far showing persistent colors.…”

mentioning

confidence: 99%

See 1 more Smart Citation

A Simply Synthesized, Tough Polyarylene with Transient Mechanochromic Response

Kempe

Brügner²,

Buchheit

et al. 2017

Angew Chem Int Ed

Self Cite

View full text Add to dashboard Cite

As imple and high-yielding route to tough polyarylenes of the type poly(meta,meta,para-phenylene) (PmmpP) is developed. PmmpP is tough even in its as-synthesized state which has an intermediate molar mass of M w % 60 kg mol À1 and exhibits outstanding mechanical properties at further optimized molecular weight of M w = 96 kg mol À1 ,E= 0.9 GPa, e = 300 %. Statistical copolymers with para,para-spiropyran (SP) are mechanochromic, and the toughness allows mechanochromism to be investigated. Strained samples instantaneously lose color upon force release.D FT calculations showt his phenomenon to be caused by the PmmpP matrix that allows build-up of sufficiently large forces to be transduced to SP,and the relatively unstable corresponding merocyanine (MC) form arising from the aromatic co-monomer.M Cu nits covalently incorporated into PmmpP show adrastically reduced half life time of 3.1 scompared to 4.5 hobtained for SP derivatives with common 6-nitro substitution.Polyarylenes have intrigued material scientists since the invention of transition-metal-catalyzed cross-coupling reactions. [1,2] In 2007, Schlüter et al. introduced ah igh molecular weight (MW) poly(meta,para-phenylene) (PmpP) by careful selection of catalyst, solvent mixture,c oncentration, and temperature. [3] In their pioneering work ac rude polymer of M w = 83 kg mol À1 was synthesized and the molecular weight further increased to M w = 255 kg mol À1 by fractionation. After fractionation, this material showed at oughness close to that of aromatic polycarbonates (E = 1GPa, e = 122 %). This was aremarkable feat both from asynthetic as well as amaterials science point of view,b ecause polyarylenes are inherently chemically more stable than polycarbonates as aresult of the exclusive presence of aryl-aryl bonds in the backbone. Subsequently,S chlüter et al. investigated various kinked polyarylenes,w ith some of them exhibiting toughness at high molecular weight after fractionation. [3][4][5][6][7] Our interest in tough polyarylenes stems from their potentially ideal use as stable,tough yet amorphous matrices for covalent incorporation of mechanochromic dyes,s uch as spiropyrans (SPs). [8][9][10] SPs isomerize to their colored merocyanine (MC) form under an umber of external stimuli, including force,and can therefore be used as mechanical force sensors. [11][12][13][14][15] Compared to matrix polymers used so far in combination with covalently linked SPs,t ough polyarylenes have several distinct advantages.T heir toughness allows drawing samples and thus to transduce mechanical force to SP.A lso,t hey are typically amorphous,h ence mechanochromism can be investigated within an isotropic matrix which is not possible with semi-crystalline polymers.H erein we show that the nature and high strength of polyarylenes is of striking additional advantage in that high forces can be transduced to SP co-monomers.We found existing methods for kinked polyarylene synthesis to be cumbersome,expensive,and inefficient owing to significant loss of polymer during fractionation. ...

show abstract

Highly Sensitive, Anisotropic, and Reversible Stress/Strain‐Sensors from Mechanochromic Nanofiber Composites

et al. 2018

Self Cite

View full text Add to dashboard Cite

Mechanochromic polymeric systems are intensively investigated for real-time stress detection applications. However, an effective stress-sensing material must respond to low deformation with a detectable color change that should be quickly reversible upon force unloading. In this work, mechanochromic nanofibers made by electrospinning are used to produce mechanochromic nanofiber/poly(dimethylsiloxane) (PDMS) composites with isotropic and anisoptropic response. Due to chain alignment of spiropyran copolymer chains within the nanofibers, only very small strains are required to yield a mechanochromic response. Composites with aligned and isotropic nanofibers show anisotropic and isotropic mechanochromic behavior, respectively. Due to the special substitution pattern of spiropyran in the copolymer, the mechanochromic response of these nanofiber/PDMS composites shows fast reversibility upon force unloading. The outstanding benefit of using highly sensitive mechanochromic nanofibers as filler in composite materials allows the detection of directional stress and strain, and it is a step forward in the development of smart, mechanically responsive materials.

show abstract

Substituent Correlations Characterized by Hammett Constants in the Spiropyran–Merocyanine Transition

Cited by 30 publications

References 49 publications

Synthesis and electrochemical evaluation of 2‐substituted imidazolium salts

Synthesis and electrochemical evaluation of 2‐substituted imidazolium salts

A Simply Synthesized, Tough Polyarylene with Transient Mechanochromic Response

Highly Sensitive, Anisotropic, and Reversible Stress/Strain‐Sensors from Mechanochromic Nanofiber Composites

Contact Info

Product

Resources

About