Donor-Substituted Diphenylacetylene Derivatives Act as Electron Donors and Acceptors

Abstract

Despite the predominant electron donor character of p-phenylenediamine, our studies on extended p-phenylenediamine derivatives show that they can not only be chemically oxidized, giving well-known Wurster-type radical cations, but also be chemically reduced, giving radical anions. Making use of EPR/ENDOR spectroscopy and supported by DFT calculations, we were able to reveal the extent of π-electron delocalization in the paramagnetic species and to shed light onto the geometry and bond lengths. While for the radical anions spin was found to be mostly delocalized into the π-system, the radical cations can be described as essentially N-centered. Furthermore, we performed electrochemical characterizations using cyclic voltammetry to gain insight into the thermodynamics of the redox processes. The photophysical properties of the parent extended p-phenylenediamine were investigated by absorption, emission, and excitation spectroscopy. The fluorescence quantum yield and the excited-state lifetime of the neutral precursors in hexane and acetonitrile were determined to establish elementary differences originating from solvent effects.

Experimental and theoretical studies of the spectroscopic properties of simple symmetrically substituted diphenylacetylene derivatives

“…1-2 ESI. † The structure of the absorption spectrum of DPA, 32,35,39 as well as dDMADPA 28,53 are in agreement with literature data. The absorption spectra of dDBADPA and dDHADPA are the same as the spectrum of dDMADPA.…”

“…Changing a solvent from non-polar MeCx to more polar MeTHF, did not cause signicant changes in the shape of the long-wavelength absorption band (Table 1, ESI †). However, in polar acetonitrile, the shape of the absorption band of dCHODPA and dDMADPA undergoes slight changes due to a loss of vibronic structure associated with the vibration of the phenyl ring, in agreement with data published by Rosspeinter et al 28 and Onitsch et al 53 (Fig. 2 ESI †).…”

“…The lowest energy vibronic band in MeCx is located at 304 nm for DPA, 316.5 nm for dOMeDPA, 326 nm for dCNDPA, 330 nm for dCOOMeDPA and 352 nm for dDMADPA. 28,53 All DPA derivatives in non-polar or weakly polar solvents possess characteristic emission band shapes that are not a mirror symmetry of the absorption spectrum. Such phenomena occurs also for the arylethynyl derivatives of DMA, 12,19 as well as for phenylene ethynylene oligomers, 22,25,26,28,54 and have been explained in terms of torsional disorder and quadratic coupling between the ground and the rst excited state 55 or the exciton model developed by Liu et al 56,57 The polarity of the solvents used in the study had little effect on the position of the emission spectra of the studied compounds.…”

Multi-coloration of polyurethane derivatives through click postfunctionalization, electrochemical oxidation, and Ag+ ion complexation

“…Very recently, the cation radical of the redox active unit of P1, namely Me 2 NPhC^CPhNMe 2 , was comprehensively investigated as an expanded W€ urster blue. 21 The reversible redox behavior of W€ urster's blue, the cation radical of N,N,N 0 ,N 0 -tetramethyl-p-phenylenediamine, has been successfully applied to electrochromic materials when this unit was integrated into polymers. 22 However, the electrochemically induced color changes of the alkyne-expanded form have, to the best of our knowledge, never been reported.…”

“…23 The g value of 2.0028 is similar to that of the reported cation radical of Me 2 NPhC^CPhNMe 2 , suggesting the aromatic amine-based cation radical. 21 The stability of the oxidized form was estimated from the time-dependent change in the absorbance intensity at 680 nm. It should be noted that the blue color was almost persistent when stored in an inert atmosphere.…”