We report the complete X-ray crystallographic structure as determined through single-crystal X-ray diffraction and a thorough theoretical analysis of the green gold Au30(S-tBu)18.\ud While the structure of Au30S(S-tBu)18 with 19 sulfur atoms has been reported, the crystal structure of Au30(S-tBu)18 without the μ3-sulfur has remained elusive until now, though matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) data unequivocally show its presence in abundance. The Au30(S-tBu)18 nanomolecule not only is distinct in its crystal structure but also has unique temperature-dependent optical properties. Structure determination allows a rigorous comparison and an excellent agreement with theoretical predictions of structure, stability, and optical response

We apply a recently developed time-dependent density functional theory (TDDFT) algorithm based on the complex dynamical polarizability to calculate the photoabsorption spectrum of the following series of closed-shell icosahedral clusters of increasing size (namely, [M13]5+, [M55]3−, [M147]−, and [M309]3+ with M = Ag, Au), focusing in particular on their plasmonic response. The new method is shown to be computationally very efficient: it simultaneously retains information on the excited-state wave function and provides a detailed analysis of the optical resonances, e.g., by employing the transition contribution map scheme. For silver clusters, a very intense plasmon resonance is found for [Ag55]3−, with strong coupling among low-energy single-particle configurations. At variance, for gold clusters we do not find a single strong plasmonic peak but rather many features of comparable intensity, with partial plasmonic behavior present only for the lowest-energy transitions. Notably, we also find a much greater sensitivity of the optical response of Ag clusters with respect to Au clusters to cluster charge, the exchange-correlation (xc) functional, and the basis set, as demonstrated via a detailed comparison between [Ag55]q and [Au55]q. The results of the TDDFT algorithm obtained with the\ud complex dynamical polarizability are finally compared with those produced by alternative (real-time evolution or Lanczos) approaches, showing that, upon proper choice of numerical parameters, overall nearly quantitative agreement is achieved among all of the considered approaches, in keeping with their fundamental equivalence

The potential tunability of the spectroscopic properties of the boron-dipyrromethene (BODIPY) parent dye by suitable functionalization makes it attractive for a number of applications. The intrinsic remarkable fluorescence of the parent compound, which strongly competes with intersystem crossing to the triplet states, can be reverted by structural tuning of the BODIPY core, leading to BODIPY derivatives suitable for photodynamic therapy purposes. With the perspective of rationally designing BODIPY derivatives with enhanced intersystem crossing, the goal of this work is two-fold: a) To investigate the main deactivation channels of the parent BODIPY following irradiation, paying particular attention to the accessibility of the triplet-state potential energy surfaces, as well as the nonradiative pathways involving the second brightest, most stable singlet electronic state S 2 , and b) to evaluate the performance of the computationally efficient second-order algebraic-dia-grammatic construction scheme for the polarization propagator (ADC(2)) against the complete active space second-order perturbation theory (CASPT2) method. Three singlet/triplet crossings were found, all of them with small spinÀorbit couplings, with the S 1 /T 2 crossing being the most plausible for the observed intersystem crossing yield. Methodologically, it is found that the ADC(2) method qualitatively reproduces the landscape of the potential energy profiles for the photophysical processes investigated; however, it systematically underestimates the energies of the stationary points and crossings of the same and different multiplicity, with the largest discrepancies found at S 1 /S 0 crossing points. Our CASPT2 results provide a comprehensive picture of the landscape of the excited-state potential energy surfaces of the parent BODIPY that might serve as a basis for the rational design of photosensitizers with a particular photophysical profile.[a] M.

Here we investigate via first-principles simulations\ud the optical absorption spectra of three different\ud Au30(SR)18 monolayer-protected clusters (MPC):\ud Au30(StBu)18, Au30(SPh)18, and Au30(SPh-pNO2)18.\ud Au30(StBu)18 is known in the literature, and its crystal structure\ud is available. In contrast, Au30(SPh)18 and Au30(SPh-pNO2)18\ud are two species that have been designed by replacing the tertbutyl\ud organic residues of Au30(StBu)18 with aromatic ones so as\ud to investigate the effects of ligand replacement on the optical\ud response of Au nanomolecules. By analogy to a previously\ud studied Au23(SR)16\ud − anionic species, despite distinct differences\ud in charge and chemical composition, a substantial ligand\ud enhancement of the absorption intensity in the optical region\ud is also obtained for the Au30(SPh-pNO2)18 MPC. The use of\ud conjugated aromatic ligands with properly chosen electron-withdrawing substituents and exhibiting steric hindrance so as to also\ud achieve charge decompression at the surface is therefore demonstrated as a general approach to enhancing the MPC\ud photoabsorption intensity in the optical region. Additionally, we here subject the ligand-enhancement phenomenon to a detailed\ud analysis based on the fragment projection of electronic excited states and on induced transition densities, leading to a better\ud understanding of the physical origin of this phenomenon, thus opening avenues to its more precise control and exploitation