Tuning luminescence of platinum complexes is well established by variation of cyclometalating ligand. The most common trend I find in literature is a red shift in the emission upon introducing more electron rich rings to the ligand (for example replacing phenyl with thiophene). I am observing the exact opposite, in which more electron rich ligands will result in blue shifted emission and was wondering what might be the possible reason ?
It depends on which position is inserted.
Pt-C gives blue shift
Pt-N gives red shift
Thanks. Is there any reference for that ?, because I see many examples for variations of the C part of ligand to give red shift.
For example : Inorg. Chem. 2016, 55, 12220-12229.
There is no simple rule in tuning the emission of Pt(II) complexes. Every ligand system is different. What one should consider is whether that (electron-rich) group is placed on a moiety acting as HOMO or LUMO. Usually F is added to the phenyl ring of a cyclometalating ligand to increase the emission energy of the metal complex. But the following paper shows that addition of F to a phenyl ring can lead to red shift. The degree to which the emission is affected also depends on the substitution pattern.
http://onlinelibrary.wiley.com/wol1/doi/10.1002/chem.201203687/abstract
Apart from this, usually we take it for granted that extending the conjugation of a ligand will lead to redshift in emission. But there are also exceptions:
Article Photophysical Properties of Cyclometalated Pt(II) Complexes:...
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