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Achieving yellow emission by varying the donor/acceptor units in rod-shaped fluorenyl-alkynyl based π-conjugated oligomers and their binuclear gold(I) alkynyl complexes

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Abstract

Fluorenyl-alkynyl based π-conjugated rod-shaped oligomers bearing different central aromatic moieties and functionalizable di-alkynyl termini, such as H–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–H (OH1), H–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Btz–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–H (OH2) and H–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Btd–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–H (OH3) where Fl = 9,9-dioctylfluorene, Btz = N-hexylbenzotriazole, and Btd = benzothiadiazole, were successfully synthesized by a Pd(0) catalyzed Stille coupling protocol. Electron withdrawing benzothiadiazole and benzotriazole as strong to moderate acceptors and fluorene as the donor have been incorporated to adjust the Donor–Acceptor (D–A) strength for fine-tuning the bandgap (Eg) as well as the emission wavelength. The corresponding digold(I) σ-complexes (PPh3)Au–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Au(PPh3) (OM1), (PPh3)Au–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Btz–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Au(PPh3) (OM2) and (PPh3)Au–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Btd–[triple bond, length as m-dash]–Fl–[triple bond, length as m-dash]–Au(PPh3) (OM3) have also been prepared by a reaction of Au(PPh3)Cl and methanolic NaOMe in DCM with the corresponding alkynyl functionalized oligomers to take advantage of the heavy-atom effect on their emissive properties. The synthesized rod-shaped π-conjugated fluorene based oligomers and their binuclear Au(I) σ-complexes have been unambiguously characterized by various spectroscopic tools such as FTIR and multinuclear NMR as well as MALDI-TOF and CHN analyses. The absorption and emission spectral studies exhibited a progressive red shift with increasing the electron withdrawing character of the central aromatic unit. The rod-like oligomers having alkynyl termini and the corresponding digold(I) complexes are found to be blue, cyan and yellow emissive, demonstrating the fine-tuning of the emission wavelength. Most importantly, the fluorene based π-conjugated yellow light emitters OH3 and OM3 are successfully achieved by varying the donor/acceptor moiety to the fluorenyl-alkynyl backbone. The digold(I) diacetylide organometallic wires exhibit phosphorescence at 77 K in degassed CH2Cl2 due to the efficient intersystem crossing from the S1 to the T1 excited state as induced by heavy atoms.

Graphical abstract: Achieving yellow emission by varying the donor/acceptor units in rod-shaped fluorenyl-alkynyl based π-conjugated oligomers and their binuclear gold(i) alkynyl complexes

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Publication details

The article was received on 12 Mar 2017, accepted on 28 Mar 2017 and first published on 30 Mar 2017


Article type: Paper
DOI: 10.1039/C7DT00895C
Citation: Dalton Trans., 2017, Advance Article
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    Achieving yellow emission by varying the donor/acceptor units in rod-shaped fluorenyl-alkynyl based π-conjugated oligomers and their binuclear gold(I) alkynyl complexes

    S. N. Islam, A. Sil and S. K. Patra, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT00895C

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