Synthesis of new, highly luminescent bis(2,2’-bithiophen-5-yl) substituted 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole

Abstract

SummaryA new synthetic approach towards the preparation of functionalised, soluble, donor–acceptor (DA) alkylbithiophene derivatives of oxadiazole, thiadiazole and triazole is reported. Taking advantage of the Fiesselmann reaction, reactive bithiophene synthons having alkyl or alkoxy substituents at designated positions are prepared. Following a synthetic strategy, featuring the bottom-up approach, sequential structural elements are built, starting from a simple thiophene compound, until the target molecule is obtained, all in good yield. Supplementing the well established methods of oxadiazole and thiadiazole synthesis, efficient ring closure reaction affording a 4H-1,2,4-triazole unit is presented. All target ambipolar compounds display strong photoluminescence with measured quantum yields up to 0.59. Modification of the demonstrated synthetic routes may be exploited for the preparation of longer, specifically functionalised oligothiophenes, coupled to other heteroaromatic cores.

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.…”

“…For both compounds the radicalc ations formed at relatively high potentials are very reactive and undergo consecutive reactions of chemical nature,l eadingt oo xidative degradation of the molecules, which is manifestedi napartial or total loss of their electrochemicala ctivity.T he same behavior was previously observed in the case of linear monomers consistingo fo xiadiazole or thiadiazole disubstituted with alkylbithiophene groups. [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.…”

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

“…The experimental findings are confronted with the results of quantum chemical (DFT) calculations delivering a mechanistic interpretation of the trends observed. Ester precursors (compounds 7a-c) of p-conjugated 1,3,4oxadiazole-thiophene derivatives (1,(3)(4)(5)(6) were prepared by the method previously elaborated, [43][44][45][46][47] starting from thiophene, 2,2 0 -bithiophene and 2,2 0 :5 0 ,2 00 -terthiophene (Scheme 1).…”

Synthesis and Optical Properties of Alkaloid Quindoline, Its Structural Analogues and Substituted δ‐Carbolines

“…Introduction of a halogen atom into the benzene core ( 2 c–e , 7 d , 7 e ) leads to a sharp decrease in the quantum yield to 0.01–0.09 (Table S1 in the SI). The observed trend of decreasing quantum yield with increasing atomic number of substituent is a clear manifestation of heavy atom effect ,. At the same time, the substituents in the benzene ring have practically no effect on the position of absorption and emission maxima in the spectra of quindoline derivatives 8 a–e , just like the quantum luminescence yield, ranging from 0.29 to 0.34.…”