Relativistic time dependent density functional calculations have been performed on the excited states of the M(CO)6 (M = Cr, Mo, W) series. Our results, in agreement with previous density functional1 and ab initio2 calculations on Cr(CO)6, indicate that in all members of the series the lowest excited states in the spectra do not correspond to ligand field (LF) excitations, as has been accepted in the past. Instead they correspond to charge transfer (CT) states. The LF excitations are calculated at much higher energy than suggested by the original assignment by Beach and Gray3 and at different energy along the M(CO)6 series, being much higher in the heavier carbonyls than in Cr(CO)6. These results lead to a definitive reassessment of the role of the LF states in the photochemical dissociation of the metal−CO bonds in the M(CO)6 series, suggesting that the experimentally observed photodissociation of the M−CO bond upon irradiation into the lowest energy bands occurs in the heavier carbonyls, as it does in Cr(CO)6, from CT and not from LF states. A comparison with the experimental data available and, in the case of Cr(CO)6, also with high-level correlated ab initio calculations2 proves the reliability of the present TDDFT approach. The choice of the exchange−correlation (XC) functional is found to have a large effect on the excitation energies, demonstrating that even for quite “normal”, low-lying excitations the XC functional may play an important role. In the heavier carbonyls, mostly in W(CO)6, relativistic effects are seen to be relevant for the LF states as well as for the CT states arising from the (2t2g)5(3t2g)1 configuration.

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The ground- and excited-state properties of a series of meso-tetraphenylporphyrin (H2TPP) diacids, [H4TPP](X)2 (X = F, Cl, Br, I), ad hoc synthesized and characterized by 1H NMR, RLS, and UV−vis spectroscopies, have been studied theoretically using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Several conformations corresponding to different deformations of the porphyrin core have been explored. The nearly degenerate purely saddled (sad) and hybrid (saddled with a small superimposed ruffling:  sadruf) conformations are the preferred “gas phase” conformations. The type and degree of distortion of the macrocycle and the orientation of the phenyl rings compare well to X-ray data available for H2TPP diacids. Two electronic structure features are key to an understanding of the optical and photophysical properties. (1) Strong interaction of the π-system of the phenyls with the π-system of the porphyrin leads to an upshift of the G-a2u (G = Gouterman) orbital and, hence, to a significant splitting of the occupied pair of a2u/a1u Gouterman orbitals. The diminished G-a2u/G-eg* gap and the lifting of the a2u/a1u degeneracy explain the red shift of the Q and B bands and the hyperchromicity of the Q-band in the diacids. (2) The highest occupied orbitals of the diacids comprise the set of halide lone pair orbitals, which move from completely above the Gouterman orbitals (I- counterion) to below them (F-). The lowest halide to porphyrin charge-transfer (HPCT) transitions are therefore predicted at very low energy (to the red of the Q-band) for Cl-−I-, but with very low intensity. Weak measured absorptions to the red of the Q-band support these theoretical findings. Quenching of the S1 (Q) state via these low-lying singlet HPCT excited states accounts for the decrease of the fluorescence quantum yield and for the measured trend along the series.

The first time-dependent DFT study of the excited states of ZnPc is presented. The theoretical results provide an accurate description of the UV−vis and vacuum−UV spectra and prove to be in excellent agreement with gas-phase spectra and generally in line with deconvolution analyses of solution and Ar/matrix absorption and MCD spectra. The nature and intensity of the main spectral features are highlighted and interpreted on the basis of the ground state electronic structure of the complex. A fragment approach where the four benzopyrrole rings and the aza bridges are taken as building blocks has proven to be a very important tool to fully understand the energy and composition of the MOs involved in the transitions and, from these, the excitation energies and intensities. The Gouterman a1u orbital is the HOMO and the assignment of the Q band is conventional and uncontroversial. The B band comprises five Eu excitations, whose positions and intensities are in very good accordance with the deconvolution of the experimental absorption band performed with the help of MCD spectra. However, this deconvolution invokes Jahn−Teller splitting of the Eu states which we have not calculated. We find at the red edge of the B band the weak 2nd π→π* transition and at the blue edge the weak n→π* transition which have been identified in the experiments. We do not confirm at low energy, in the tail of the Q band (the “Q02” region) an electronic origin for the band which has been suggested to arise from the lowest z-polarized n→π* transition. This transition is predicted by our calculations to be very weak and to lie in the B band region. The energies and intensities of the higher excitations are in excellent agreement with the UV N and L bands and with the far UV C and X bands. The predicted level pattern of the lowest triplet excited states fits in with phosphorescence data available and excited-state absorption spectra

Reported herein is a combination of experimental and DFT/TDDFT theoretical investigations of the ground and excited states of 1,4,8,11,15,18,22,25-Octabutoxyphthalocyaninato-nickel(II), NiPc(BuO)(8), and the dynamics of its deactivation after excitation into the S(1)(pi,pi) state in toluene solution. According to X-ray crystallographic analysis NiPc(BuO)(8) has a highly saddled structure in the solid state. However, DFT studies suggest that in solution the complex is likely to flap from one D(2)(d)-saddled conformation to the opposite one through a D(4)(h)-planar structure. The spectral and kinetic changes for the complex in toluene are understood in terms of the 730 nm excitation light generating a primarily excited S(1) (pi,pi) state that transforms initially into a vibrationally hot (3)(d(z)2,d(x)2(-)(y)2) state. Cooling to the zeroth state is complete after ca. 8 ps. The cold (d,d) state converted to its daughter state, the (3)LMCT (pi,d(x)2(-)(y)2), which itself decays to the ground state with a lifetime of 640 ps. The proposed deactivation mechanism applies to the D(2)(d)-saddled and the D(4)(h)-planar structure as well. The results presented here for NiPc(BuO)(8) suggest that in nickel phthalocyanines the (1,3)LMCT (pi,d(x)2(-)(y)2) states may provide effective routes for radiationless deactivation of the (1,3)(pi,pi) states.