Enhanced Dual Visible Light Fluorescence from the 2,2‘-Dipyridyl Tungsten Alkylidyne Complex [W(⋮CC₆H₄NMe₂-4)(O₂CCF₃)(CO)₂{κ²-2,2‘-(NC₅H₄)₂}]:  An Organometallic Twisted Intramolecular Charge Transfer State

Abstract

The N,N-dimethylanilino tungsten alkylidyne complex [W(⋮CC6H4NMe2-4)(O2CCF3)(CO)2(NC5H4Me-4)2] has been synthesized, characterized, and employed as a precursor to neutral and cationic 2,2‘-dipyridyl and TMEDA (N,N,N‘,N‘-tetramethylethylenediamine) complexes, which display dual blue and yellow fluorescences in CH2Cl2 solutions at ambient temperatures with surprisingly high quantum yields for this class of organometallic complex. The efficiencies of the radiative emissions from the 2,2‘-dipyridyl complex [W(⋮CC6H4NMe2-4)(O2CCF3)(CO)2{κ2-2,2‘-(NC5H4)2}] are particularly impressive. The dual nature of the emissions (λem ≈ 450 and 540−580 nm) is attributed to independent, short-lived (ns) “twisted intramolecular charge transfer” (1TICT) and 1dW−π*W ⋮ CAr states, respectively, the former being well understood in organic aromatic systems, but yet to be described for organometallic complexes.

Anti-Kasha’s Rule Fluorescence Emission in (2-Ferrocenyl)indene Generated by a Twisted Intramolecular Charge-Transfer (TICT) Process

“…Comparison with complexes in which a methylated indene moiety is present allows one to better understand the behavior of (2-ferrocenyl)indene. A TICT process was previously reported, to our knowledge, only in some organometallic compounds, such as N , N -dimethylanilino tungsten alkylidyne complexes, but with a mechanism not directly involving the metal center.…”

FRET Sensitization of Tungsten–Alkylidyne Complexes by Zinc Porphyrins in Self-Assembled Dyads

“…Metal–alkylidyne (−carbyne) complexes possess an unusual combination of properties that make them attractive for applications in artificial photosynthesis. Many of these compounds possess long-lived excited states that are controllable by variation of the metal, d-electron configuration (d 0 , d 1 , d 2 ), and ancillary ligands. − Further, some derivatives undergo proton- and H-atom transfer reactions − that could be coupled to excited-state redox processes for photochemically driving proton-coupled electron-transfer reactions such as reduction of CO 2 . , One limitation of metal–alkylidyne compounds is that they do not typically possess strong visible-wavelength electronic-absorption bands. For the broad class of d 2 configured luminophores of the form M(CR)L 4 X, the allowed d→π*(MCR) orbital transition that results in population of the emissive dπ* state is relatively weak (ε ≈ 10 2 M –1 cm –1 ) due to its d–d parentage .…”

Electrocatalytic reductive dimerization of the 2,2′-bipyridyl tungsten alkylidyne complex [W(CC6H4NMe2-4)(NCMe)(CO)2{κ2-2,2′-(NC5H4)2}]+

“…This again serves to emphasize the independence of the 2,2 0 -bipyridyl-based LUMO from the cis-ligand which is itself trans to the alkylidyne carbon atom. Given the stabilization of the LUMO in complex 2 relative to that of complex 1 and the observation that the m max (CO) peaks from the IR spectra for complexes 1 (1973, 1888 cm À1 ) and 2 (1981, 1900 cm À1 ) ( Table 1) are not all that different, in addition to the similar 13 C NMR chemical shifts of the alkylidyne carbons [d 281.3 (1) and 282.1 (2)] [4], one might conclude that the level of electron density on the W"C core is invariant between the two complexes despite their charge difference. The 2,2 0 -bipyridyl ligand therefore bears much of the brunt of the electronic charge depreciation upon forming 2 from 1.…”

“…[4]) with a CH Instruments electrochemical analyzer. All potentials were measured relative to an Ag/AgNO 3 (MeCN, 10 mM) reference electrode at 20°C and quoted relative to an internal standard comprising the ferrocene/ ferrocenium couple.…”