posted on 2023-05-17, 14:31authored byRobinson, R, Raphael Karikachery, A, Sharp, PR
The six-membered platinacycle complex, Pt(tBu2bpy)(C6H4OC6H4) (6) (tBu2bpy = 4,4¡ä-di-tert-butyl-2,2¡ä-bipyridine) has been prepared from Pt(tBu2bpy)Cl2 and 2,2¡ä-dilithio-diphenyl ether. Platinacycle 6 and its analogs with X = CH2 (4) and NMe (5) exhibit intense solid-state photoluminescence and nearly identical crystal structures. The photophysical properties of 4¨C6 in the visible range are dominated by mixed metal¨Cligand-to-ligand charge transfer (MLL¡äCT) transitions involving high-lying filled mixed metal¨Cligand orbitals (ML), composed primarily of platinacyclic ring-based d- and ¦Ð-orbitals, and a low lying vacant ¦Ð* orbital (L¡ä) of the tBu2bpy ligand. Lone pair donation from the bridging oxygen atom and especially the NMe group increases the energy of the mixed metal¨Cligand orbital (ML) without altering the energy of the tBu2bpy ¦Ð* orbital. As a result, the MLL¡äCT state energy decreases and the absorption and emission wavelengths are red-shifted. DFT and TD-DFT calculations support the experimental results. Additional calculations on the unknown platinacycles with X = CO (7) and SO2 (8) predict a blue-shift for the MLL¡äCT absorption and emission. Two nearly equal energy triplet minima were located on the DFT triplet surface for 4¨C6. One of these (4T¨C6T) has a geometry very similar to the ground-state singlet (as represented by 4¨C6) and is associated with the emissive 3MLL¡äCT excited state. The other triplet-state (4T¡ä¨C6T¡ä) has a distorted structure where the platinacycle ring is twisted out of the Pt(tBu2bpy) plane. Thermal access to this distorted triplet may be responsible for the loss of photoluminescence in room temperature solutions of 4¨C6.
History
Publication title
Dalton Transactions
Volume
41
Issue
9
Pagination
2601-2611
ISSN
1477-9226
Department/School
School of Natural Sciences
Publisher
Royal Soc Chemistry
Place of publication
Thomas Graham House, Science Park, Milton Rd, Cambridge, England, Cambs, Cb4 0Wf