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Er III ‐Cored Complexes Based on Dendritic Pt II –Porphyrin Ligands: Synthesis, Near‐IR Emission Enhancement, and Photophysical Studies
Author(s) -
Oh J. B.,
Nah M.K.,
Kim Y. H.,
Kang M. S.,
Ka J.W.,
Kim H. K.
Publication year - 2007
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200600451
Subject(s) - excited state , porphyrin , dendrimer , luminescence , photochemistry , ligand (biochemistry) , quantum yield , moiety , materials science , ion , crystallography , fluorescence , chemistry , stereochemistry , polymer chemistry , organic chemistry , atomic physics , biochemistry , physics , receptor , optoelectronics , quantum mechanics
A series of stable and inert complexes with Er III cores and dendritic Pt II ‐porphyrin ligands exhibit strong near‐IR (NIR) emission bands via highly efficient energy transfer from the excited triplet state of the Pt II ‐porphyrin ligand to Er 3+ ions. The NIR emission intensity of thin films of Er III complexes at 1530 nm, originating from 4f–4f electronic transitions from the first excited state ( 4 I 13/2 ) to the ground state ( 4 I 15/2 ) of the Er 3+ ion, is dramatically enhanced upon increasing the generation number ( n ) of the aryl ether dendrons because of site‐isolation and light‐harvesting (LH) effects. Attempts are made to distinguish the site‐isolation effect from the LH effect in these complexes. Surprisingly, the site‐isolation effect is dominant over the LH effect in the Er 3+ ‐[G n ‐PtP] 3 (terpy) (terpy: 2,2′:6′,2″‐terpyridine) series of complexes, even though the present dendrimer systems with Er III cores have a proper cascade‐type energy gradient. This might be due to the low quantum yield of the aryl ether dendrons. Thus, the NIR emission intensity of Er 3+ ‐[G3‐PtP] 3 (terpy) is 30 times stronger than that of Er 3+ ‐[G1‐PtP] 3 (terpy). The energy transfer efficiency between the Pt II ‐porphyrin moiety in the dendritic Pt II ‐porphyrin ligands and the Ln 3+ ion increases with increasing generation number of the dendrons from 12–43 %. The time‐resolved luminescence spectra in the NIR region show monoexponential decays with a luminescence lifetime of 0.98 μs for Er 3+ ‐[G1‐PtP] 3 (terpy), 1.64 μs for Er 3+ ‐[G2‐PtP] 3 (terpy), and 6.85 μs for Er 3+ ‐[G3‐PtP] 3 (terpy) in thin films of these complexes. All the Er III ‐cored dendrimer complexes exhibit excellent thermal stability and photostability, and possess good solubility in common organic solvents.