The Synthesis, Characterization and Photophysics of a New Class of Inorganic Ligands for Metal-Metal Multiply Bonded Compounds Christopher B. Durr

Metal Based Polymers Intermediate Energy MLCT nm Low Energy MLCT nm High Energy  -  * nm Solar Spectrum

Ground State  h ** Excitation S1S1 SnSn Intersystem Crossing Triplet Emission Singlet Emission T1T1 Probe h

Chromium Carbonyl Model Complex: Synthesis

L  * Mo 2  * Mo 2  eV eV eV eV Cr d  –CO  * L  *, Mo 2  Mo 2 (O 2 C Ph) 2 Mo 2 [O 2 CBnCr(CO) 3 ] eV 3.14 eV Mo 2 , Cr d x2-y2 LUMO+1 LUMO HOMO

fs-Transient Absorption Spectroscopy Mo 2 [O 2 CBnCr(CO) 3 ] 2, ex = 515 nm in DCM 3.5 ps -1 ps 0.4 ps 1.8 ps 0.9 ps 9.5 ps 500 ps 2000 ps 1000 ps 25 ps 100 ps fs-TA Spectroscopy shows a transient at ~575 nm that decays with a lifetime of ~17 ps which indicates a 1 MLCT singlet state.

35 min 0 min 45 min 10 min 150 min 5 min 105 min 90 min 170 min 20 min Light Dark 210 min 20 hours 5.50 ps -6.8 ps 264 ps 0.53 ps 2.53 ps 2830 ps 1.35 ps 11.7 ps 948 ps 29.4 ps 73.6 ps fs Time-Resolved Infrared Spectroscopy Mo 2 [O 2 CBnCr(CO) 3 ] 2, ex = 515 nm

ns-Transient Absorption  = 24  s ns-Transient Absorption showed a bleach at ~500 nm which indicates a long lived excited state that lasts for 24.3  1.9  s Near IR emission indicates a  * Triplet State due to its location ~1100 nm and its vibronic features which correlate to the MM stretch.

Mo 2 [PTA-ReCl(CO) 3 ] 2 (TiPB) 2 : Model Complex

L  * Mo 2  * Mo 2  eV eV eV L  eV Re d  -CO  *, Mo 2  eV Re d  -CO  * L  *, Mo 2  eV Mo 2 PTA Mo 2 [PTAReCl(CO) 3 ] eV 2.28 eV LUMO+1 LUMO HOMO

fs-Transient Absorption Spectroscopy Mo 2 [PTAReCl(CO) 3 ] 2, ex = 675 nm in THF τ = 16.8 ± 0.8 ps 40 ps -1 ps 1500 ps 0.3 ps 2.5 ps 0.6 ps 17.5 ps 7.5 ps 150 ps 500 ps fs-TA Spectroscopy shows a transient at ~475 nm that decays with a lifetime of ~17 ps which indicates a 1 MLCT singlet state.

fs Time-Resolved Infrared Spectroscopy Mo 2 [PTAReCl(CO) 3 ] 2, ex = 675 nm 29.1 ps -6 ps 1140 ps 0.39 ps 2.24 ps 0.80 ps 11.4 ps 5.21 ps 73.3 ps 2830 ps 264 ps gs IR τ = 16.4 ± 0.2 ps

ns-Transient Absorption  = 21  s Near-IR Emission confirms a  * triplet state due to vibrational transitions corresponding to MM bond stretch. The transient absorption shows both a bleach and a transient that lasts for ~21  s.

Conclusions DFT calculations show that molecular orbitals can be tuned based on the metals used and their interactions with the ligands. Singlet states are 1 MLCT based lasting less than 20 ps, and can be studied in greater depth using TR- IR. (Friday, Infrared/Raman Symposium: 11:25 AM) Triplet states are relatively long lived (~25  s), and are  * in the case of Mo 2 dinuclear centers. Further studies with different metals and bonding interactions could shed light on the photophysics of both the MM multiple bond and previously studied inorganic systems.

Acknowledgements Dr. Malcolm Chisholm Dr. Claudia Turro Dr. Terry Gustafson Dr. Vesal Naseri Samantha Brown-Xu Thomas Spilker