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On the effect of conformational isomerism on the optical properties of bis(8-oxyquinolato) diboron complexes with 2,2’-biphenyl backbone

Abstract

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 imposing close intramolecular p-stacking interactions involving chromophore units. Crystal structure of 1 revealed a unique p-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 terminal phenyl group and Q ligand, dominates in benzene and chloromethanes solutions. The observed conformational equilibria strongly affects the optical properties of the system, specifically leading to significant increase of quantum yield of emission (from 22% in MeCN to 38% in benzene) accompanied by 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 variation in frontier orbitals distributions.

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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, Accepted Manuscript
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    On the effect of conformational isomerism on the optical properties of bis(8-oxyquinolato) diboron complexes with 2,2’-biphenyl backbone

    M. Urban, P. Górka, K. Nawara, K. Wozniak, K. Durka and S. Lulinski, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT03197E

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