Thiophene–Thiophene versus Phenyl–Phenyl Coupling in 2‐(Diphenylamino)‐Thiophenes: An ESR‐UV/Vis/NIR Spectroelectrochemical Study

Abstract

The oxidation of several 2‐diphenylamino‐substituted thiophenes and N,N′‐bis(2‐diphenylamino‐5‐thienyl)‐substituted phenylene‐1,4‐diamines with different substitution patterns in the 5‐position of their thiophene moieties was studied by cyclovoltammetric and spectroelectrochemical measurements (ESR, UV/Vis/NIR). These measurements revealed both the structure of the oxidation products obtained and that of their cationic intermediates, as well as the pathway of their formation and follow‐up reactions. Thus, the formation of the radical cations in the first electrochemical oxidation step of the target molecules was demonstrated. Depending on the substitution pattern, these radical cations give rise to several consecutive processes to a different extent. Thus radical dimers, dehydrodimers with a 2,2‐bithiophene, 3,3′‐bithiophene, or benzidine structure, as well as radical monocationic and dicationic products can be formed. For N,N′‐bis(2‐diphenylamino‐5‐thienyl)‐substituted phenylene‐1,4‐diamines rather stable radical cations and dications were primarily formed and unambiguously identified. These species were transformed into 2,2′‐bithiophene dimers and oligomers when the 5‐position of the thiophene moiety was unsubstituted. By in situ spectroelectrochemistry the influence of the substituents on the type of coupling reactions can be demonstrated and followed in detail.

Electronic descriptors for analytical use of the benzidine‐based compounds and the mechanism of oxidative coupling of anilines

“…This transition is the most intense (f = 1.489) and has a small half-width in the experimental spectrum. [4,6] This absorption band is rather well predicted by all DFT functionals, except the B3LYP (Table 2). It should be noted that this band corresponds the second transition in the spectrum calculated in vacuum approximation ( Table 4).…”

“…Experimental value is equal to 429 nm. [4,6] ANALYTICAL USE OF THE BENZIDINE-BASED COMPOUNDS The state S 17 in Fig. 1a corresponds to the main contribution (39% HOMO → LUMO + 5) presented in Table 4, but it may seem that this is a transition HOMO → LUMO + 4 (Fig.…”

“…Earlier, a few proposals were reported regarding this mechanism. [1][2][3][4]6,8,14,16] From these studies, one can highlight three points of view on the reaction mechanism. An attempt of explanation of the aforementioned mechanism is presented in Zaporozhets et al; [5] however, just a general molecular sequence (C 6 H 5 N(C 2 H 5 ) 2 → Teb → Teb 2+ ) is shown as the stages of the oxidative coupling.…”

“…[1,2] After cooling their melts, they generally form amorphous glasses in which charged species, generated by their oxidation, exhibit high stability and high mobility. [4] Meanwhile, N-alkylated amines and diamines, such as N,Ndiethylaniline or N,N,N′,N′-tetraethylbenzidine (Teb), have been recently reported to be effective reagents for colorimetric and visual determination of the ClO À , BrO 3 À , and IO 3 À ions in wastewater. [5] This method is based on the well-known reaction of electrochemical [1][2][3][4]6] or chemical oxidation of the amines with different oxidants.…”

“…[5] This method is based on the well-known reaction of electrochemical [1][2][3][4]6] or chemical oxidation of the amines with different oxidants. Among them, the naphthalene-1,8-diylbis (diphenylmethylium) ion, [7] atomic chlorine, [8] and such ions as ClO 4 À , [9,10] Cu 2+ , [9,11] Cr 2 O 7 2À , [10,12] S 2 O 8 2À , [12][13][14] Ti 3+ , [15] Ce 4+ , MnO 4 À -anion [12] were effectively utilized to obtain singly and doubly ionized forms of the aforementioned amines. Overall, the latter dications are rather stable-colored species that were comprehensively studied by UV-Vis spectroscopic techniques.…”