Phosphorescent, liquid-crystalline complexes of platinum(II): influence of the beta-diketonate co-ligand on mesomorphism and emission properties

TY - JOUR

T1 - Phosphorescent, liquid-crystalline complexes of platinum(II)

T2 - influence of the beta-diketonate co-ligand on mesomorphism and emission properties

AU - Spencer, Matthew

AU - Santoro, Amedeo

AU - Freeman, Gemma R.

AU - Diez, Alvaro

AU - Murray, Paul R.

AU - Torroba, Javier

AU - Whitwood, Adrian C.

AU - Yellowlees, Lesley J.

AU - Williams, J. A. Gareth

AU - Bruce, Duncan W.

PY - 2012/12/21

Y1 - 2012/12/21

N2 - Two series of rod-like ortho-platinated complexes bound to a range of beta-diketonate co-ligands are reported of the form [Pt(N boolean AND C)(O boolean AND O)]. The liquid crystal and luminescent properties are influenced through the introduction of different beta-diketonates (O boolean AND O) as well as through the presence of a fused cyclopentene ring on the N boolean AND C-coordinated 2-phenylpyridine ligand. For metal complexes, smectic phases are dominant but no mesomorphism is exhibited when the beta-diketonate is hexafluorinated acetylacetonate (1,1,1-5,5,5-hexafluoro-2,4-pentandione). The introduction of an unsymmetrical trifluoroacetyl acetonate (1,1,1-trifluoro-2,4-pentandione) ligand is particularly interesting due to the discovery of the beta-diketonate as a dynamic system that readily isomerises to a 1 : 1 ratio under thermal conditions, from an initial ratio of 3 : 1 formed during the synthesis. As expected, the presence of the 3,5-heptanedionato co-ligand decreases the transition temperatures due to the introduction of a larger lateral substituent. Unfortunately complexes based on 2-phenylpyridine ligands with a fused cyclopentene ring are, with one exception, not mesomorphic. With the exception of the hexafluoroacetyl acetonate complexes, the materials are brightly luminescent and have excited state lifetimes between 13 and 30 mu s with emission quantum efficiencies exceeding 0.5, with one as high as 0.7. A time-dependent density functional theory (TD-DFT) study suggests that the lack of emission from the hexafluoroacetyl acetonate complexes may be associated with large structural distortion upon formation of the excited state, as well as to poorer overlap of orbitals leading to a lower radiative rate constant. The same analysis provides an explanation for the apparently quite different emission efficiencies of the two isomers of the trifluoroacetyl acetonate complexes.

AB - Two series of rod-like ortho-platinated complexes bound to a range of beta-diketonate co-ligands are reported of the form [Pt(N boolean AND C)(O boolean AND O)]. The liquid crystal and luminescent properties are influenced through the introduction of different beta-diketonates (O boolean AND O) as well as through the presence of a fused cyclopentene ring on the N boolean AND C-coordinated 2-phenylpyridine ligand. For metal complexes, smectic phases are dominant but no mesomorphism is exhibited when the beta-diketonate is hexafluorinated acetylacetonate (1,1,1-5,5,5-hexafluoro-2,4-pentandione). The introduction of an unsymmetrical trifluoroacetyl acetonate (1,1,1-trifluoro-2,4-pentandione) ligand is particularly interesting due to the discovery of the beta-diketonate as a dynamic system that readily isomerises to a 1 : 1 ratio under thermal conditions, from an initial ratio of 3 : 1 formed during the synthesis. As expected, the presence of the 3,5-heptanedionato co-ligand decreases the transition temperatures due to the introduction of a larger lateral substituent. Unfortunately complexes based on 2-phenylpyridine ligands with a fused cyclopentene ring are, with one exception, not mesomorphic. With the exception of the hexafluoroacetyl acetonate complexes, the materials are brightly luminescent and have excited state lifetimes between 13 and 30 mu s with emission quantum efficiencies exceeding 0.5, with one as high as 0.7. A time-dependent density functional theory (TD-DFT) study suggests that the lack of emission from the hexafluoroacetyl acetonate complexes may be associated with large structural distortion upon formation of the excited state, as well as to poorer overlap of orbitals leading to a lower radiative rate constant. The same analysis provides an explanation for the apparently quite different emission efficiencies of the two isomers of the trifluoroacetyl acetonate complexes.

UR - http://www.scopus.com/inward/record.url?scp=84866890143&partnerID=8YFLogxK

U2 - 10.1039/c2dt31525d

DO - 10.1039/c2dt31525d

M3 - Article

SN - 1477-9226

VL - 41

SP - 14244

EP - 14256

JO - Dalton Transactions

JF - Dalton Transactions

IS - 47

ER -