Resonance-Enhanced Charge Delocalization in Carbazole–Oligoyne–Oxadiazole Conjugates

Abstract

There are notably few literature reports of electron donor-acceptor oligoynes although they offer unique opportunities for studying charge transport through 'all-carbon' molecular bridges. In this context, the current study focuses on a series of carbazole-(C≡C) n -2,5-diphenyl-1,3,4-oxadiazoles (n = 1-4) as conjugated π-systems, in general, and explores their photophysical properties, in particular. Contrary to the behavior of typical electron donor-acceptor systems, for these oligoynes the rates of charge recombination after photoexcitation increase with increasing electron donoracceptor distance. To elucidate this unusual performance, detailed photophysical and time-dependent density functional theory investigations were conducted. Significant delocalization of the electron density along the bridge indicates that the bridging states come into resonance with either the electron donor or acceptor, thereby accelerating the charge transfer. Moreover, the calculated bond lengths reveal a reduction in bond length alternation upon photoexcitation, indicating significant cumulenic character of the bridge in the excited state. In short, strong vibronic coupling between the electrondonating N-arylcarbazoles and the electron-accepting 1,3,4-oxadiazoles accelerates the charge recombination as the oligoyne becomes longer.

Nuclearity Control for Efficient Thermally Activated Delayed Fluorescence in a CuI Complex and its Halogen-Bridged Dimer

“…Thus, singlet and triplet excitons generated under electrical excitation in electroluminescent devices can be used through the singlet harvesting effect − to reach up to a 100% internal efficiency, whereas a limit of only 25% is expected in the absence of TADF or phosphorescence. Although phosphorescent emitters can achieve such an efficiency through a triplet harvesting mechanism, they often require high-cost and less abundant Ir­(III) or Pt­(II) ions in their structure. − Conversely, the most studied TADF emitters correspond to purely organic compounds ,− or low-cost metal-based inorganic complexes containing Cu I ,,− or Ag I . ,,− Hence, a deep understanding and identification of the variables controlling TADF is required to design and develop high-performance emitters for technological applications.…”

A review of functional linear carbon chains (oligoynes, polyynes, cumulenes) and their applications as molecular wires in molecular electronics and optoelectronics

“…20) was probed recently using in-depth photophysical and time-dependent DFT (TD-DFT) techniques. 166 The overall absorption characteristics gave rise to a strong length dependence of the bridge, and, as above, a dramatic reduction in PLQY accompanied increasing oligoyne length. Solvent-polarity-dependent emission measurements were reported.…”

Advances in Polyynes to Model Carbyne

“…There is a strong correlation between energy/wavenumber of the Я line and BLA in polyynes, 68 and the signals move consistently to lower values as BLA decreases. 69 Experimentally, this dispersion is clearly by comparison of the Raman frequency of a tetrayne (2257−2000 cm −1 ) to the longest derivative in each case, Tr* [20]/Py* [16]/Ad [10]/Re [10] (1918/1922/1985/ 1899 cm −1 ).…”