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Ultrafast Excited State Dynamics Controlling Photochemical Isomerization of N ‐Methyl‐4‐[ trans ‐2‐(4‐pyridyl)ethenyl]pyridinium Coordinated to a {Re I (CO) 3 (2,2′‐bipyridine)} Chromophore
Author(s) -
Busby Michael,
Hartl František,
Matousek Pavel,
Towrie Mike,
Vlček Antonín
Publication year - 2008
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.200800188
Subject(s) - excited state , photochemistry , isomerization , chemistry , resonance raman spectroscopy , photoisomerization , pyridinium , photodissociation , spectroscopy , resonance (particle physics) , quantum yield , population , raman spectroscopy , fluorescence , medicinal chemistry , physics , demography , particle physics , quantum mechanics , sociology , nuclear physics , optics , catalysis , biochemistry
Two multifunctional photoactive complexes [Re(Cl)(CO) 3 (MeDpe + ) 2 ] 2+ and [Re(MeDpe + )(CO) 3 (bpy)] 2+ (MeDpe + = N ‐methyl‐4‐[ trans ‐2‐(4‐pyridyl)ethenyl]pyridinium, bpy=2,2′‐bipyridine) were synthesized, characterized, and their redox and photonic properties were investigated by cyclic voltammetry; ultraviolet–visible–infrared (UV/Vis/IR) spectroelectrochemistry, stationary UV/Vis and resonance Raman spectroscopy; photolysis; picosecond time‐resolved absorption spectroscopy in the visible and infrared regions; and time‐resolved resonance Raman spectroscopy. The first reduction step of either complex occurs at about −1.1 V versus Fc/Fc + and is localized at MeDpe + . Reduction alone does not induce a trans → cis isomerization of MeDpe + . [Re(Cl)(CO) 3 (MeDpe + ) 2 ] 2+ is photostable, while [Re(MeDpe + )(CO) 3 (bpy)] 2+ and free MeDpe + isomerize under near‐UV irradiation. The lowest excited state of [Re(Cl)(CO) 3 (MeDpe + ) 2 ] 2+ has been identified as the Re(Cl)(CO) 3 →MeDpe + 3 M LCT (MLCT=metal‐to‐ligand charge transfer), decaying directly to the ground state with lifetimes of ≈42 (73 %) and ≈430 ps (27 %). Optical excitation of [Re(MeDpe + )(CO) 3 (bpy)] 2+ leads to population of Re(CO) 3 →MeDpe + and Re(CO) 3 →bpy 3 M LCT states, from which a MeDpe + localized intraligand 3 ππ* excited state ( 3 IL) is populated with lifetimes of ≈0.6 and ≈10 ps, respectively. The 3 IL state undergoes a ≈21 ps internal rotation, which eventually produces the cis isomer on a much longer timescale. The different excited‐state behavior of the two complexes and the absence of thermodynamically favorable interligand electron transfer in excited [Re(MeDpe + )(CO) 3 (bpy)] 2+ reflect the fine energetic balance between excited states of different orbital origin, which can be tuned by subtle structural variations. The complex [Re(MeDpe + )(CO) 3 (bpy)] 2+ emerges as a prototypical, multifunctional species with complementary redox and photonic behavior.