Calculated triplet excited state potential energy surfaces are presented for a set of three bis-tridentate Ru II-polypyridyl dyes covering a wide range of room temperature excited state lifetimes: [Ru II(tpy) 2] 2+, 250 ps; [Ru II(bmp) 2] 2+, 15 ns; and [Ru II(dqp) 2] 2+, 3 μs (tpy is 2,2′:6′,2″-terpyridine, bmp is 6-(2-picolyl)-2,2′-bipyridine, and dqp is 2,6-di(quinolin-8-yl)pyridine). The computational results provide a multidimensional view of the 3MLCT- 3MC transition for the investigated complexes. Recently reported results of significantly prolonged 3MLCT excited state lifetimes of bis-tridentate Ru II-complexes, for example [Ru II(dqp) 2] 2+, are found to correlate with substantial differences in their triplet excited state multidimensional potential energy surfaces. In addition to identification of low-energy transition paths for 3MLCT- 3MC conversion associated with simultaneous elongation of two or more Ru-N bonds for all investigated complexes, the calculations also suggest significant differences in 3MLCT state volume in the multidimensional reaction coordinate space formed from various combinations of Ru-N bond distance variations. This is proposed to be an important aspect for understanding the large differences in experimentally observed 3MLCT excited state lifetimes. The results demonstrate the advantage of considering multidimensional potential energy surfaces beyond the Franck-Condon region in order to predict photophysical and photochemical properties of bis-tridentate Ru II-polypyridyl dyes and related metal complexes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry