Quadruply bonded M 2 complexes incorporating thienylvinyl carboxylates Carly R. Reed, Malcolm H. Chisholm, Claudia Turro th International Symposium on Molecular Spectroscopy

Incorporating Dimetal Units into Conjugated Organic Polymers Conjugated organic polymers find application in optoelectronic devices such as OLEDs, and OPVs. Oligothiophenes are an important class of organic conjugated polymers; interesting due to their small band gap, excellent charge conductivity, and easy synthesis. Incorporating quadruply bonded dimetal units into conjugated organic polymers is of interest to determine new tunable optoelectronic properties. M = Mo, W Macromol. Chem. Phys. 2008, 209, 1319

M = Mo, W Synthesis of Complexes L = “Bis-bis” complex Goals: Compare electronic coupling through the metal center as the metal is varied (Mo v. W) and compare photophysical properties of complexes as metal center is varied.

Orbital Interactions in bis-bis Complexes There are two  * combinations of the carboxylate ligands – the out-of-phase combination can interact with the metal orbitals. Back-bonding stabilizes the metal based orbital and destabilizes the ligand  * orbital. The splitting between the  * orbitals is an indication of the amount of the electronic coupling; the greater the splitting the greater the coupling. The splitting depends on the character of the metal center and the conjugation of the ligand.

Mo 2 (TiPB) 2 (L) 2  E of L  * = 0.30, 0.37 W 2 (TiPB) 2 (L) eV (L  * out of phase) eV (L  * in phase) eV  E = 2.72 eV eV eV eV eV eV  E = 2.24 eV eV eV L = eV (W 2  ) Density Functional Theory Calculations DFT calculations utilized B3LYP functional with basis set 6-31G* for non-metal atoms and SDD basis set with effective core potential for the metal atoms.

Electrochemical Exploration of Electronic Coupling When reduced (adding an electron to the thiophene ligand based LUMO) will these complexes exhibit charge delocalization through the metal center onto both “arms” or will the charge remain localized on one ligand? or [LM 2 L] [LM 2 L] -1 [LM 2 L] -2 Small (E 2 0 – E 1 0 ) Localized Large (E 2 0 – E 1 0 ) Delocalized

CompoundOxidation Potential Reduction Potential 1 Reduction Potential 2 Reduction Potential 3  E (mV) Mo 2 (O 2 C(CH) 2 Thiophene) V V V169.0 W 2 (O 2 C(CH) 2 Thiophene) V V V V (  E 2, 3) In 0.1M Bu 4 NPF 6 in THF versus ferrocene/ferrocenium couple, a. Inorg. Chem. 48, Greater splitting in W 2 (versus Mo 2 ) reveals greater electronic coupling through the metal center. Electrochemistry

L    * MLCT    * Absorption Spectroscopy Mo 2 W2W2

W2W2 Emissive Properties

exc = 514 nm  = 1.6 ± 0.02 ps exc = 532 nm Mo 2 MoW W 2 1 MLCT 3  * 514 nm 1055 nm,  = 38  s Mo nm  = 1.6 ps

W2W2 W 2, MoW, Mo 2 Mo 2 MoW W 2 Single emission from 1 MLCT No long lived excited state detectable on ns time scale. Not relaxing through a 3  * excited state.

Conclusions and Future Work Thienylvinyl carboxylate complexes containing W 2 are more delocalized than Mo 2 complexes when reduced. Mo 2 and W 2 thienylvinyl carboxylate complexes do not have the same type of long lived triplet excited states. Plan to isolate the Mo 2 and W 2 bis-bis thienylethynyl carboxylate complexes. Compare the photophysical properties and electrochemical properties of the thienylethynyl complexes to the thienylvinyl.

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