화학공학소재연구정보센터
Inorganic Chemistry, Vol.54, No.19, 9438-9446, 2015
Electronic and Spectroscopic Properties of Avobenzone Derivatives Attached to Ditungsten Quadruple Bonds
From the reactions between W-2((TPB)-P-i)(4), where T'PB is 2,4,6-triisopropylbenzoate, and 2 equiv of acid, 4-formylbenzoic acid, HBzald, 4-(3-oxo-3-phenylpropanoyObenzoic acid, HAvo, or 4-(2,2-difluoro-6-phenyl-2H-1 lambda(3),3,2 lambda(4)-dioxaborinin-4-yl)benzoic acid, HAvoBF(2), three new compounds W-2((TPB)-P-i)(2)(Bzald)(2), I, W-2((TPB)-P-i)(2)(Avo)(2), II, and W-2((TPB)-P-i)(2)(AvoBF(2))(2), III, have been prepared. As solid compounds I and II are blue while compound III is green. Characterization of these compounds has been carried out by means of H-1 NMR, MALDI-TOF MS, steady-state absorption and emission spectroscopies, and femtosecond and nanosecond transient absorption and time-resolved infrared spectroscopies. Compounds I and II have strong metal to ligand charge transfer, MLCT, transitions in the visible region of their spectra while compound III exhibits MLCT absorption in the nearinfrared (lambda(max) = 1017 nm). All three have S-1 states that have corresponding lifetimes of similar to 3-30 ps and are (MLCT)-M-1 in character. The triplet states are (MLCT)-M-3 with lifetimes in the range 3-10 ns. Density functional theory and time-dependent density functional theory were employed to perform electronic structure calculations in order to aid in the interpretation of these data. The spectroscopic properties of I and II are similar while the planarity of the ligand in III greatly lowers the energy of the MLCT state. The W-2 unit enables direct observation of intersystem crossing from the (MLCT)-M-1 state to (MLCT)-M-3 state via the use of ultrafast spectroscopy.