Effect of regioregularity and role of heteroatom on the chiral behavior of oligo(heteroalkyl thiophene)s

Abstract

Novel optically active oligothiophenes bearing electron‐donating chiral side chains have been prepared by synthetic methods suitable to achieve regioregular head‐to‐tail and head‐to‐head/tail‐to‐tail derivatives. In particular, the chiral (S)‐(2‐methyl)butyl moiety was linked at position 3 of the thiophene ring through heteroatoms, such as S or O, to evaluate its effect on the macro molecular aggregation and, consequently, on the chiroptical properties of the material in the solid state. The materials have been fully characterized and investigated by optical and chiroptical methods upon aggregation both from the solution and as cast films. Compared with the related head‐to‐tail and head‐to‐head/tail‐to‐tail poly(3‐alkyl)thiophene derivatives, with the same optically active moiety directly linked to the ring and possessing a higher polymerization degree, the chiroptical properties of the newly synthesized oligomers were significant, or even better, and provided insight into the role of intrachain–interchain interactions between the heteroatom and the thienyl sulfur atom.

Chiral Polythiophenes: Part I: Syntheses of Monomeric Precursors

“…One of the representatives is alkoxy substituted thiophene with an electro-donating substituent, optically active (+)-3-[( S )-(2-methylbutoxy)]thiophene (TOR*) 57, which was prepared in 67% yield by the acid catalyzed reaction of 3-methoxythiophene 55 with ( S )-(−)-2-methyl-1-butanol 3 refluxed in a toluene solution for 24 h in the presence of a catalytic amounts of p -toluenesulfonic acid monohydrate ( Scheme 17 ) [ 67 ].…”

“…As an example, 3-[(−) 3-( S )-3,7-dimethyoctyl]thiophene 15 was converted to (−) 2–bromo-3-( S )-(3,7-dimethyoctyl)thiophene 63 [ 72 , 73 , 74 ]; (+)-3-[2-(( S )-2- methylbutoxy)ethyl]thiophene 24 to (+)-2-bromo-3-[2-(( S )-2- methylbutoxy)ethyl]thiophene 64[ 50 ] [ 50 , 51 , 75 ]; (+)- 3-[( S ) -2-methylbutylsulfanyl]thiophene 59 to the corresponding 2-bromo derivative 65 [ 67 , 68 , 70 ]; (+)-3- [( S )-3,7-dimethyloctylsulfanyl]thiophene 61 to 2-bromo derivative 66 [ 70 ] and ( R )-3-(4-(4-ethyl-2-oxazolin-2-yl)phenyl)thiophene (EOPT) 18 to EOPT-Br 67 ( Scheme 20 ) [ 47 ].…”

“…An analogous reaction of optically active 3-[2-(1- methyloctyloxy)ethyl]thiophene 75 afforded either the monobromothiophene 75 or dibromothiophene 77, dependent on the amount of NBS used ( Scheme 24 , Entry 3) [ 78 ]. Fully regioselective dibromination was again observed for 3-[2-methylbutylsulfanyl]thiophene 59 , giving the corresponding 2.5-dibromo derivative 78 ( Scheme 24 , Entry 4) [ 67 , 68 , 70 , 79 ]; (+)-3- [( S )-3,7-dimethyloctylsulfanyl]thiophene 61, leading to 2,5-dibromo derivative 79 ( Scheme 24 , Entry 5) [ 80 ] and (+)-3-[( S ) -2-methylbutoxyl]thiophene 57, giving the corresponding 2.5-dibromo derivative 80 ( Scheme 24 , Entry 6) [ 67 ].…”

“…One of the representatives is alkoxy substituted thiophene with an electro-donating substituent, optically active (+)-3-[(S)-(2-methylbutoxy)]thiophene (TOR*) 57, which was prepared in 67% yield by the acid catalyzed reaction of 3-methoxythiophene 55 with (S)-(−)-2-methyl-1-butanol 3 refluxed in a toluene solution for 24 h in the presence of a catalytic amounts of p-toluenesulfonic acid monohydrate (Scheme 17) [67]. The monomer (S)-57 was used to prepare novel, optically active oligothiophenes using synthetic methods suitable for obtaining regioregular head-to-tail and head-tohead/tail-to-tail derivatives (if starting from the bithiophene monomers).…”

“…The optical properties of the polythiophenes with different types of substitution were examined using UV-VIS and fluorescent spectroscopy, and the circular dichroism and polarimetric measurements were conducted to examine their chirality. The fluorescence quantum efficiency in the solutions of the regioirregularly 2,5-coupled polythiophenes reaches 24%.The synthesis of the 3-substituted monothiophenes containing an alkyl side chain attached to the thiophene ring through a heteroatom was developed, as the presence of the heteroatom directly attached to the heterocyclic ring affects the properties of the monomers as well the products of their polymerizations.One of the representatives is alkoxy substituted thiophene with an electro-donating substituent, optically active (+)-3-[(S)-(2-methylbutoxy)]thiophene (TOR*) 57, which was prepared in 67% yield by the acid catalyzed reaction of 3-methoxythiophene 55 with (S)-(−)-2-methyl-1-butanol 3 refluxed in a toluene solution for 24 h in the presence of a catalytic amounts of p-toluenesulfonic acid monohydrate (Scheme 17)[67].…”