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Excited State Tuning of Bis(tridentate) Ruthenium(II) Polypyridine Chromophores by Push–Pull Effects and Bite Angle Optimization: A Comprehensive Experimental and Theoretical Study
Author(s) -
Breivogel Aaron,
Meister Michael,
Förster Christoph,
Laquai Frédéric,
Heinze Katja
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201302231
Subject(s) - ruthenium , chromophore , excited state , chemistry , photochemistry , materials science , catalysis , atomic physics , physics , organic chemistry
Abstract The synergy of push–pull substitution and enlarged ligand bite angles has been used in functionalized heteroleptic bis(tridentate) polypyridine complexes of ruthenium(II) to shift the 1 MLCT absorption and the 3 MLCT emission to lower energy, enhance the emission quantum yield, and to prolong the 3 MLCT excited‐state lifetime. In these complexes, that is, [Ru(ddpd)(EtOOC‐tpy)][PF 6 ] 2 , [Ru(ddpd‐NH 2 )(EtOOC‐tpy)][PF 6 ] 2 , [Ru(ddpd){(MeOOC) 3 ‐tpy}][PF 6 ] 2 , and [Ru(ddpd‐NH 2 ){(EtOOC) 3 ‐tpy}][PF 6 ] 2 the combination of the electron‐accepting 2,2′;6′,2′′‐terpyridine (tpy) ligand equipped with one or three COOR substituents with the electron‐donating N , N ′‐dimethyl‐ N , N ′‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) ligand decorated with none or one NH 2 group enforces spatially separated and orthogonal frontier orbitals with a small HOMO–LUMO gap resulting in low‐energy 1 MLCT and 3 MLCT states. The extended bite angle of the ddpd ligand increases the ligand field splitting and pushes the deactivating 3 MC state to higher energy. The properties of the new isomerically pure mixed ligand complexes have been studied by using electrochemistry, UV/Vis absorption spectroscopy, static and time‐resolved luminescence spectroscopy, and transient absorption spectroscopy. The experimental data were rationalized by using density functional calculations on differently charged species (charge n =0–4) and on triplet excited states ( 3 MLCT and 3 MC) as well as by time‐dependent density functional calculations (excited singlet states).