Dramatically Enhanced Fluorescence of Heteroaromatic Chromophores upon Insertion as Spacers into Oligo(triacetylene)s

Abstract

Dedicated to Professor David N. Reinhoudt on the occasion of his 60th birthdayIn continuation of a previous study on the modulation of p-electron conjugation of oligo(triacetylene)s by insertion of central hetero-spacer fragments between two (E)-hex-3-ene-1,5-diyne ((E)-1,2-diethynylethene, DEE) moieties (Fig. 1), a new series of trimeric hybrid oligomers (14 ± 18 and 22 ± 24, Fig. 2) were prepared (Schemes 1 ± 3). Spacers used were both electron-deficient (quinoxaline-based heterocycles, pyridazine) and electron-rich (2,2'-bithiophene, 9,9-dioctyl-9H-fluorene) chromophores. With 19 ± 21 (Scheme 4), a series of transition metal complexes was synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramolecular assembly. The UV/VIS spectra ( Fig. 3) revealed that the majority of spacers provided heterotrimers featuring extended p-electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer 13 and homo-trimer 12 (Fig. 5). This increase in emission intensity appears as a general feature of these systems: even if the spacer molecule is non-fluorescent, the corresponding hetero-trimer may show a strong emission ( Table 2). The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV) ( Table 3 and Fig. 5). In each case, the first one-electron reduction step in the hetero-trimers appeared anodically shifted compared with DEE dimer 13 and homo-trimer 12. With larger spacer chromophore extending into two dimensions (as in 14 ± 18, Fig. 2), the anodic shift (by 240 ± 490 mV, Table 3) seems to originate from inductive effects of the two strongly electron-accepting DEE substituents rather than from extended p-electron conjugation along the oligomeric backbone, as had previously been observed for DEE-substituted porphyrins.Introduction. ± In a previous study, we had explored how the properties of oligomers made from (E)-1,2-diethynylethene (DEE, (E)-hex-3-ene-1,5-diyne) repeating units can be tuned or changed by the insertion of spacer chromophores [1]. For this purpose, a series of eleven hybrid oligomers 1 ± 11 (Fig. 1) were prepared, in which mostly aromatic hetero-spacers with different electronic characteristics were introduced between two DEE moieties. UV/VIS Studies revealed that the majority of the hetero-spacers were less effective than the homo-spacer DEE in trimeric 12 in facilitating p-electron delocalization along the linear conjugated oligomeric backbone. Electrochemical investigations by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV) confirmed these results.On the other hand, fluorescence studies clearly demonstrated that a desirable function can be created or strongly enhanced upon insertion of hetero-spacers into pure DEE oligomers [2 ± 4]. Thus, the heterocyclic derivatives 7 ± 9, containing pyridine, pyrazine, or thiophene spacers, respectively, feature a strong fluorescence emission, which is present to a signi...

A New Donor–Acceptor–Donor Polyfluorene Copolymer with Balanced Electron and Hole Mobility

“…All other chemicals were purchased from Aldrich and were used without further purification. The following compounds were synthesized following modified literature procedures: the diketone 7 [25], 4,7-dibromo-2,1,3-benzothiadiazole [21], 1,4-dibromo-2,3-diaminobenzene 3 [21], and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9,9-dioctylfluorene [22].…”

“…Bromination of 2,1,3-benzothiadiazole (1) with Br 2 and HBr gave 4,7-dibromo-2,1,3-benzothiadiazole (2), which was subsequently reduced with zinc in acetic acid to afford 1,4-bibromo-2,3-diaminobenzene (3). [21] Condensation of compound 3 with diketone 7 followed by Stille coupling of quinoxaline 8 with 2-tributylstannylthiophene afforded compound 9. Bromination of compound 9 with N-bromosuccinimide (NBS) resulted in dibromide 10, which was subsequently copolymerized with 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9,9-dioctylfluorene [22] to afford APFO-15.…”

Electronic Properties and Field‐Effect Transistors of Thiophene‐Based Donor–Acceptor Conjugated Copolymers

“…The monomers 2,5-bis(trimethylstannyl)thiophene [6] and 5,8-dibromo-2,3-diheptylquinoxaline were synthesized following reported methods. [7] High-purity HPLC grade trifluoroacetic acid and chloroform were used to make polymer solutions. The anhydrous toluene and octyltrichlorosilane (OTS) used in the deposition of self-assembled monolayers (SAMs) on the gate dielectric surface were purchased from Aldrich and used as received.…”

New Donor‐Functionalized Cp Ligands: Synthesis and Complexation Behaviour of Quinoxalyl and Benzothiadiazolyl Systems

“…Solvents were dried by using standard procedures and distilled prior to use. 4,7-dibromo-2,1,3-benzothiadiazole 17 , di-µ- ). Infrared spectra were obtained on a Varian 3100 FT-IR spectrometer (Excalibur Series).…”