Hi,

It is very well known that many Pt(II) complexes exhibit emissive properties, in contrast there are very few examples of highly emissive Pd(II) complexes. The non allowed quantum transitions due to heavy atom effect is exhibited to a much higher degree in Pt(II) complexes because the Pt(II) is heavier than Pd(II).

Compare the Pt(II) and Pd(II) sections in this review it will give You a more detailed answer.

Cheers,

Kaspars

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Also, this may be help,

http://pubs.acs.org/doi/abs/10.1021/acs.macromol.7b00171?src=recsys&journalCode=mamobx

There is also a number of articles that directly compare Pt(II) with Pd(II) analogs. In these systems low temperatures (below 77K) were required to cause emission. Hope this helps:

http://pubs.acs.org/doi/pdf/10.1021/ic50217a029

http://pubs.acs.org/doi/pdf/10.1021/ic50166a015

I think whether palladium(II) complexes are photoluminescent or not depends largely on their non-radiative decay rates (knr). It should be noted that the ISC rates of Pd(II) complexes are comparable to those of Pt(II) complexes. One major difference in photophysical properties between Pd(II) and Pt(II) complexes is their radiative decay rates (kr). Pd(II) complexes usually have a lower kr (i.e. slow-emitting) due to the lack of metal character in the triplet excited state. As a result, given the same degree of knr, the Pt(II) complex can be emissive at room temperature but the Pd(II) complex cannot. Hope this helps.

Some related articles:

http://onlinelibrary.wiley.com/wol1/doi/10.1002/anie.201305590/full

http://pubs.rsc.org/en/Content/ArticleLanding/2016/SC/C6SC00462H#!divAbstract

http://onlinelibrary.wiley.com/wol1/doi/10.1002/asia.201301059/full

http://pubs.acs.org/doi/abs/10.1021/ic991089g