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Issue 44, 2018
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The effect of conformational isomerism on the optical properties of bis(8-oxyquinolato) diboron complexes with a 2,2′-biphenyl backbone

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Abstract

A fluorescent bis(8-oxyquinolato) diborinic complex with a central 2,2′-biphenyl backbone 1 and its octafluoro analogue 2 were synthesized to study the optical–structural relationship of sterically encumbered molecules featuring close intramolecular π-stacking interactions involving chromophore units. The crystal structure of 1 revealed a unique π-stacked arrangement of two pendant phenyl groups and two 8-oxyquinolato ligands (Q) located in the inner part of the complex. Unlike 1, the closely related complex 2 features conformational isomerism, and two major forms, namely 2-syn and 2-anti, are observed in solution to a varying extent depending on the solvent polarity. Form 2-syn, a geometrical analogue of 1, is preferable in polar solutions, whereas its rotational isomer 2-anti featuring π-stacking interactions between the terminal phenyl group and Q ligand dominates in benzene and chloromethane solutions. The observed conformational equilibria strongly affect the optical properties of the system, specifically leading to a significant increase of the quantum yield of emission (from 22% in MeCN to 38% in benzene) accompanied by a bathochromic shift (Δλ = 10 nm) of absorption and hypsochromic shifts (Δλ = −8 nm) of emission spectra with decreasing solvent polarity. This effect was ascribed to the variation in frontier orbital distributions.

Graphical abstract: The effect of conformational isomerism on the optical properties of bis(8-oxyquinolato) diboron complexes with a 2,2′-biphenyl backbone

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Publication details

The article was received on 05 Aug 2018, accepted on 11 Sep 2018 and first published on 12 Sep 2018


Article type: Paper
DOI: 10.1039/C8DT03197E
Citation: Dalton Trans., 2018,47, 15670-15684
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    The effect of conformational isomerism on the optical properties of bis(8-oxyquinolato) diboron complexes with a 2,2′-biphenyl backbone

    M. Urban, P. Górka, K. Nawara, K. Woźniak, K. Durka and S. Luliński, Dalton Trans., 2018, 47, 15670
    DOI: 10.1039/C8DT03197E

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