Effect of donor to acceptor ratio on electrochemical and spectroscopic properties of oligoalkylthiophene 1,3,4-oxadiazole derivatives

Abstract

A structure-property study across a series of donor-acceptor-donor structures composed of mono- and bi-(1,3,4-oxadiazole) units symmetrically substituted with alkyl functionalized bi-, ter- and quaterthiophene segments is presented. Synthetically tailoring the ratio of electron-withdrawing 1,3,4-oxadiazole to electron-releasing thiophene units and their alkyl grafting pattern permitted us to scrutinize the impact of these structural factors on the redox, absorptive and emissive properties of these push-pull molecules. Contrasting trends of redox potentials were observed, with the oxidation potential closely following the donor-to-acceptor ratio, whereas the reduction potential being tuned independently by either the number of acceptor units or the conjugation length of the donor-acceptor system. Increasing the thiophene unit contribution delivered a shift from blue to green luminescence, while the structural rigidity afforded by intramolecular non-covalent interactions between 1,3,4-oxadiazole and the thiophene moieties has been identified as the prime factor determining the emission efficiency of these molecules. All six structures investigated electro-polymerize easily, yielding electroactive and electrochromic polymers. The polymer doping process is largely influenced by the length of the oligothiophene repeating unit and the alkyl chain grafting density. Polymers with relatively short oligothiophene segments are able to support polarons and polaron-pairs, whereas those with segments longer than six thiophene units could also stabilize diamagnetic charge carries - bipolarons. Increasing the alkyl chain grafting density improved the reversibility and broadened the working potential window of the p-doping process. Stable radical anions have also been investigated, bringing detailed information about the conjugation pattern of these electron-surplus species. This study delivers interesting clues towards the conscious structural design of bespoke frontier energy level oligothiophene functional materials and their polymers by incorporating a structurally matching 1,3,4-oxadiazole unit.

Selenylated-oxadiazoles as promising DNA intercalators: Synthesis, electronic structure, DNA interaction and cleavage

“…2). As expected, compounds 3a-h presented a reduction process at the most negative potentials, probably associated with the oxadiazole group [57]. Compound 3e showed different reduction behavior due to the electroactivity of the nitro group.…”

“…Analysis of the data listed in Table 1 leads to the conclusion that the IP and EA energies depend directly on the electron-donating or electronwithdrawing characteristics of the substituent group. The introduction of electron donor groups increases the electron density and therefore decreases the oxidation potential and the IP [57,61], 3g with the dimethylamino substituent in the phenyl portion directly linked to the selenium atom, showed this effect more pronouncedly. This effect was also observed on molecules 3b, 3c and 3d, in which oxidation starts at less anodic values, however the electron donor substituent is linked to the phenyl portion closest to oxadiazole.…”

Time‐dependent density functional theory investigations on structural modification in carbazole‐based organic photosensitizers to improve electron injection in dye‐sensitized solar cell

“…The addition of electrophilic heterocyclic molecules with thiophene in the π ‐spacer can produce such changes in energy levels, which are favorable for photosensitizers. [ 51,52,54 ] Oxadiazole is an efficient electron acceptor with elevated thermal stability and photoluminescence quantum yield. [ 55 ] The oxadiazole has high compatibility with thiophene because of their structural similarities.…”

Investigating the Optical Properties of Thiophene Additions to s-Indacene Donors with Diketopyrrolopyrrole, Isoindigo, and Thienothiophene Acceptors

“…Yamaguchi et al found that longer conjugated systems and longer conjugated D–A systems of the same type had an increase in both QY and emission maximum . However, Kurowska et al found in small molecule D–A systems that the QY decreased and the emission maximum increased with an increase in the donor ratio . Surprisingly, there has not been much investigation of conjugation length of the donor in D–A polymers with tailored donor and acceptor subunits.…”

“…99 However, Kurowska et al found in small molecule D−A systems that the QY decreased and the emission maximum increased with an increase in the donor ratio. 100 Surprisingly, there has not been much investigation of conjugation length of the donor in D−A polymers with tailored donor and acceptor subunits. The polymers in this study with longer donor conjugation lengths had higher QYs than their corresponding shorter donor polymer analogues.…”