Photophysical Studies of trans-Bis(phenylethynyldiisopropylamidinato)bis(acetato)dimetal Complexes Involving MM Quadruple Bonds Where M = Mo or W

Abstract

The title compounds trans-M(2)(O(2)CMe)(2)[C((i)PrN)(2)C≡C-Ph](2), I (M = Mo) and II (M = W), show electronic absorptions in the visible region of the spectrum assignable to (1)MLCT [M(2)δ to phenylethynylamidinate π*]. These compounds show dual emission from S(1) and T(1) states. For both I and II, S(1) is (1)MLCT, but for I the T(1) state is shown to be MMδδ* while for II T(1) is (3)MLCT. The lifetimes of the S(1) and T(1) states have been determined by femtosecond and nanosecond transient absorption spectroscopy: for I S(1) ∼ 20 ps and T(1) ∼ 100 μs and for II S(1) ∼ 6 ps and T(1) ∼ 5 μs. From solvent dependence of the absorption and emission spectra, we suggest that the S(1) states are localized on one amidinate ligand though the initial absorption is to a delocalized state.

Electron delocalization in the S 1 and T 1 metal-to-ligand charge transfer states of trans -substituted metal quadruply bonded complexes

“…However for II, our interpretation of the solvent dependence is that the initial absorption occurs without a significant change in dipole moment whereas that associated with the emission from the S 1 states is significant (14). Because the ground state molecules are symmetrical (D 2h ) and have a center of inversion, the Franck-Condon absorption conserves the point group symmetry to place the excited electron (14). The vibronic spacing together with the lack of solvent dependence in the T 1 state emission for II is consistent with the assignment of this state as the 3 MoMoδδ Ã state.…”

“…The more limited range of solubilities of compounds I and I 0 made the solvent dependent study less clear. However for II, our interpretation of the solvent dependence is that the initial absorption occurs without a significant change in dipole moment whereas that associated with the emission from the S 1 states is significant (14). Because the ground state molecules are symmetrical (D 2h ) and have a center of inversion, the Franck-Condon absorption conserves the point group symmetry to place the excited electron (14).…”

“…S3 and S4), II (14), and II 0 (14) each emit from both the S 1 and T 1 states. In compound I 0 , the T 1 -S 0 energy gap is estimated to be small and this favors nonradiative decay so only emission from the S 1 state is observed (Figs.…”

Tuning the electronic structure of Mo–Mo quadruple bonds by N for O for S substitution

“…16,17 Investigations by Chisholm and coworkers on the photoexcited states of trans-[M 2 (TiPB) 2 (O 2 CR) 2 ] (R = 2-thiophene 18,19 or C 6 H 4 -4-CN; TiPB = 2,4,6-triisopropylbenzoate) 20 show emission from T 1 states that are about the dimetal core also makes MM multiply bonded paddlewheel compounds good candidates for incorporation into materials with potentially interesting optoelectronic properties. [21][22][23][24][25][26][27] This was highlighted in a detailed study by Zhou and co-workers which demonstrated that the shape and size of molecular architectures formed using dicarboxylate ligands to bridge Mo 2 4+ units can be controlled by tuning the bridging angle and size of the bridging dicarboxylate ligand.…”

Electronic structure and spectroscopy of homoleptic compounds of dimolybdenum using TDDFT

“…25 Several recent papers have studied the different cases of dymolibdenum compounds with special ligands. [26][27][28][29][30][31][32][33][34][35] A complete revision of these is out of the scope of this study. Some of them use DFT as a tool for understanding the structure of these compounds [30][31][32][33][34][35] .…”