Effect of the electron-accepting centre and solubilising substituents on the redox, spectroscopic and electroluminescent properties of four oxadiazoles and a triazole disubstituted with bithiophene

Star‐Shaped Conjugated Molecules with Oxa‐ or Thiadiazole Bithiophene Side Arms

“…Vibrational structure, although not very highly pronounced, is observed in the emission spectrao fm olecules with two alkyl substituents (S*TBT2 and S*OBT2),w hich may be interpreted in terms of some rigidification of the molecular structure in the excited state, possibly throughb enzoid-quinoid type of transformationo ccurringu pon excitation. [41] Relatively large Stokes shifts are measured for S*TBT1 and S*OBT1, 90 and 104 nm, respectively.T hey are larger than the shifts reported for the corresponding linear compounds containing oxadiazoleo rt hiadiazole units [37][38][39][40] and additionally corroborate significant,e xcitation-induced changesint heir molecular structure. Smaller Stokes shifts are found for S*TBT2 and S*OBT2 (59 and 71 nm) comparable to those noted for the linear compounds.…”

“…As ar esult, the electrochemical gaps (E g (electro)) of S*TBT1 and S*TBT2 are smaller than those of S*OBT1 and S*OBT2.T he trend is similara si nt he case of linear donor-acceptor compounds consisting of the same electron-withdrawing and -donating groups, however,i nt he star-shaped molecules the electrochemical band gaps are smaller by 120 to 170 meV. [39,40] Figure 2. Cyclic voltammograms of the studied star-shaped molecules (concentration 510 À4 m in 0.1 m Bu 4 NPF 6 /CH 2 Cl 2 ;scan rate:5 0mVs À1 ).…”

“…Although trisubstituted benzene as the central unit of the studied star-shaped molecules should assure their good planarity and conjugation, the planarity-sensitive p-p*b and in the spectra of these molecules is hypsochromically shiftedb y 13 to 16 nm, as compared to the case of the corresponding linear oxa-or thiadiazoles disubstituted with either alkylbithiophene or dialkylbithiophene. [37,39,40] The p-p*b and in the thin film spectra of molecules containing one alkyl solubilizing group in each arm (S*TBT1 and S*OBT1) is bathochromically shifted with respect to the position of this band in the solution spectra (see Table 1). This means that lower planarity of these molecules in solution has its origin in the interaction with the solvent molecules and in the solid state this planarity is improved.…”

“…[38,43] The reduction process of all four molecules is irreversible, similarly as linear oxa-and thiadiazoles disubstitutedw ith alkyl-o r dialkylbithiophenes ( Figure 2). [37,39,40] Molecules containing thiadiazole electron withdrawing units are easier to reduce and easier to oxidize as compared to their oxadiazole analogues (see Figure2and data presented in Ta ble 2) yielding lower ionization potential (IP) and highere lectron affinity (EA) values. As ar esult, the electrochemical gaps (E g (electro)) of S*TBT1 and S*TBT2 are smaller than those of S*OBT1 and S*OBT2.T he trend is similara si nt he case of linear donor-acceptor compounds consisting of the same electron-withdrawing and -donating groups, however,i nt he star-shaped molecules the electrochemical band gaps are smaller by 120 to 170 meV.…”

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

“…38 Both the electron-withdrawing character of 1,3,4-oxadiazole and its efficient conjugation with thiophene afford versatile tuning of electronic properties of thiophene based molecular structures. 36,39 Furthermore, oxygen and nitrogen atoms can engage in non-covalent interactions with sulphur and hydrogen atoms of adjacent thiophene units. 38 In the anti-conformation, one can expect the formation of hydrogen bonds between oxadiazole's oxygen atom and the two hydrogen atoms of the flanking thiophenes, 40 while each of the two symmetric azole nitrogens could couple with the nearest thiophene's sulphur atom by way of cooperative heteroatomic interactions.…”