Theoretical studies on structures and spectroscopic properties of self-assembled bis(2,4,8,10-tetramethyl-9-methoxycarbonylethyldipyrrin-3-yl)methane with Co(II).

We report a combined experimental and computational study of the large self-assembly complex (CoL)(2) [L= bis(2,4,8,10-tetramethyl-9-methoxycarbonylethyldipyrrin-3-yl)methane] containing 172 atoms. An extensive density functional theory (DFT) and time-dependent DFT study of this complex in gas phase and in CH(2)Cl(2) solution was performed, investigating the effect of substitutions of methyl and methyl propionate on the electronic structure and optical properties of this complex. The calculated IR and Raman spectra are in excellent agreement with the experiment, thus allowing a detailed assignment of the vibrational absorption bands. Comparing the vibrational spectrum of (CoL)(2) with that of (ZnL')(2) [L' = bis(2,4-dimethyldipyrrin-3-yl)methane], the substitution of methyl on the C(beta) atom results in sizable shifts on the same modes; particularly in the case of mode upsilon(C(beta)-C(beta)), the shift is more than 20 cm(-1). The lowest 70 singlet-singlet spin-allowed excited states were taken into account for the calculation by TDDFT in gas phase and PCM-TDDFT in CH(2)Cl(2) solution. Theoretical calculations provide a good description on positions of the two band maximums in observed spectrum but predict a contrary relatively intensity for these two bands. In the UV-vis absorption spectrum of (CoL)(2) complex, the band maximum at 525.5 nm is mainly attributed to the pi-->pi* transition. The band maximum at 488.1 nm is originated from metal-ligand charge-transfer (MLCT) transition mixed with interligand pi-->pi* transition.