Synthesis, characterization, and electrogenerated chemiluminescence of phenyl-substituted, phenyl-annulated, and spirofluorenyl-bridged oligothiophenes

Abstract

To overcome the insolubility of higher oligothiophenes and simultaneously to enhance their processability with respect to an application in molecularly doped organic light-emitting devices (OLEDs) we synthesized phenylsubstituted, phenyl-annulated, and spirofluorenyl-bridged oligothiophenes 1-5. Significantly improved solubilities in polar solvents of up to three orders of magnitude were found and their optical and electrochemical properties were investigated in solution. Reflecting small conformational changes and the almost complete electronic separation of the substituents, phenyl substitution and the introduction of a spiro core by bridging the central bithienyl unit only slightly affected optical and redox properties in comparison to the unmodified oligothiophenes (6-8). In contrast, the presence of an isothianaphthene (benzo[c]thiophene) unit in the oligomeric chain led to a distinct approximation of the frontier orbitals and consequently to a red-shift of both absorption and fluorescence. Finally, we demonstrated the applicability of some oligomers as dopants for OLEDs by electrogenerated chemiluminescence (ECL).

Electrochemistry and electrogenerated chemiluminescence of thiophene and fluorene oligomers. Benzoyl peroxide as a coreactant for oligomerization of thiophene dimers

“…Most previous studies of oligothiophenes have focused on oxidation, with fewer studies of reduction being reported in the literature. 67 Presumably, this reflects the fact that the reductions in question typically occur at quite negative potentials and that oxidations are more frequently used in (p-type) doping of polythiophene polymers. One goal of the present study was thus to carry out analyses of a set of congeneric oligothiophenes under conditions of both oxidation and reduction.…”

“…Several studies on the ECL behavior of some thiophene and spirofluorene oligomers have been previously reported. 38,67,[77][78][79][80] In this work the ECL spectra for oligomers with a large number of units, n, were obtained. In terms of length, this corresponds to a maximum n value of seven in the case of the fluorenes and twelve in the case of the thiophenes.…”

4,4′‐Spirobi[cyclopenta[2,1‐b;3,4‐b′]dithiophene: A New Generation of Heterocyclic Spiro‐Type Molecules

“…Considerable works have been done in order to replace the phenyl units of the core unit with less aromatic heteroaryl units such as thiophene. However, these efforts were only partially successful, resulting for example in a core unit with mixed chromophores between a bifluorene and a bithienyl unit [19,20] or a phenyl-thiophenyl and a bifluorene unit [21][22][23] or in a thiophene based core unit with a silicon atom at the centre of the spiro core. [24] In this paper we report for the first time on a new spiro type molecule with only thiophene as a central aromatic system with a spiro carbon atom, giving the core unit 4,4′-spirobi[cyclopenta[2,1-b;3,4-b′]dithiophene] (Spiro-CPDT).…”

Electroluminescent Properties of Spiro[fluorene-benzofluorene]-Containing Blue Light Emitting Materials

“…However, spiro compounds with versatile substituents, especially spiro[fuorene-benzofluorene] with an asymmetric substitution pattern on the fluorine and benzofluorene units, have seldom been reported. [11][12][13][14][15][16] Recently, we have successfully demonstrated that the spiro[fluorene-7,9′-benzofluorene]-based host and dopant materials can form a blue OLED with a good color purity. [17][18][19][20][21][22] In this study, new host materials based on the new spiro-[fluorene-7,9′-benzofluorene]-based materials, BH-1P and BH-1DPA, were designed and synthesized by the Suzuki reaction and amination reaction in order to improve the EL efficiency and color purity of the OLEDs.…”