Metallosupramolecular architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, molecular recognition, and sensing. For the most part these achievements have been made with high-symmetry metallosupramolecular architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallosupramolecular architectures that are made up of multiple different ligands and/or metals ions in order to obtain more complex systems with new properties. Herein we show that the addition of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis(pyridin-3-ylethynyl)pyridine (2A-tripy), to a solution of the [Pd2(tripy)4](4+) cage resulted in the clean generation of a heteroleptic [Pd2(tripy)2(2A-tripy)2](4+) architecture. The formation of the mixed-ligand cage [Pd2(tripy)2(2A-tripy)2](4+) was confirmed using (1)H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resolution electrospray ionization mass spectrometry. Density functional theory calculations suggested the cis isomer was more stable that the trans isomer. Additionally, the calculations indicated that the heteroleptic palladium(II) cages are kinetically metastable intermediates rather than the thermodynamic product of the reaction. Competition experiments supported that finding and showed the cages are long-lived in solution at room temperature. Finally, it was shown that the addition of 2A-tripy to a range of preformed [Pd2(Ltripy)4](4+) cages cleanly generated the mixed-ligand systems. Three other systems displaying different exo and endo functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized heteroleptic cis-[Pd2(La)2(Lb)2](4+) cages.

The synthesis, optical characterization and computational modeling of seven benzo[c][1,2,5]thiadiazole (BTD) donor-acceptor dyes are reported. These dyes have been studied using electrochemical analysis, electronic absorption, emission, and Raman and resonance Raman spectroscopies coupled with various density functional theoretical approaches. Crystal structure geometries on a number of these compounds are also reported. The optical spectra are dominated by low energy charge-transfer states; this may be modulated by the coupling between donor and acceptor through variation in donor energy, variation of the donor-acceptor torsion angle, and incorporation of an insulating bridge. These modifications result in a perturbation of the excitation energy for this charge-transfer transition of up to ∼2000 cm(-1). Emission spectra exhibit significant solvatochromisim, with Lippert-Mataga analysis yielding Δμ between 8 and 33 D. Predicted λmax, ε, and Raman cross sections calculated by M06L, B3LYP, PBE0, M06, CAM-B3LYP, and ωB97XD DFT functionals were compared to experimental results and analyzed using multivariate analysis, which shows that hybrid functionals with 20-27% HF best predict ground state absorption, while long-range corrected functionals best predict molecular polarizabilities.

Design of nanometer scale artificial light harvesting and charge separating proteins enables reengineering to overcome the limitations of natural selection for efficient systems that better meet human energetic needs.

A series of dipyrido[3,2-a:2',3'-c]phenazine (dppz)-based ligands with electron-withdrawing substituents and their [Re(CO)3(L)Cl] and [Re(CO)3(L)(py)]PF6 complexes have been studied using Raman, resonance Raman, and transient resonance Raman (TR(2)) and time-resolved infrared (TRIR) spectroscopic techinques in conjunction with computational chemistry as well as electrochemical studies, emission, and absorption of ground and excited states. DFT (B3LYP) frequency calculations show good agreement with nonresonant Raman spectra, which allowed these to be used to identify phenanthroline, phenazine, and delocalized modes. These band assignments were used to establish the nature of chromophores active in resonance Raman spectra, probed with wavelengths between 350.7 and 457.9 nm. X-ray crystallography of [Re(CO)3(dppzBr2)Cl] and [Re(CO)3(dppzBr)(py)]PF6 showed these crystallize in space groups triclinic P1 and monoclinic P2(1/n), respectively. Electrochemical studies showed that substituents have a strong effect on the phenazine MO, changing the reduction potential by 200 mV. Transient absorption studies showed that generally the [Re(CO)3(L)(py)]PF6 complexes had longer lifetimes than the corresponding [Re(CO)3(L)Cl] complexes; the probed state is likely to be (3)π → π* (phz) in nature. TR(2) spectra of the ligands provided a marker for the triplet π → π* state, and the TR(2) spectra of the complexes suggest an intraligand (IL) π,π* state for [Re(CO)3(L)(py)](+) complexes, and a potentially mixed IL/MLCT state for [Re(CO)3(L)Cl] complexes. TRIR spectroscopy is more definitive with THEXI state assignments, and analysis of the metal-carbonyl region (1800-2100 cm(-1)) on the picosecond and nanosecond time scales indicates the formation of MLCT(phen/phz) states for all [Re(CO)3(L)Cl] complexes, and IL π → π* (phen) states for all [Re(CO)3(L)(py)](+) complexes, with all but [Re(CO)3(dppzBr(CF3))(py)](+) showing some contribution from an MLCT(phen) state also.

A 2,2'-bipyridine-appended bis(ferrocene) three tiered molecular folding ruler, can be switched from a folded conformation to an extended conformation by the addition of [Cu(CHCN)](PF) and 6,6'-dimesityl-2,2'-bipyridine. This extension and contraction process could be triggered either chemically or electrochemically and was reversible.

The synthesis, spectroscopic characterization, and computational modeling of seven benzo[ c][2,1,3]thiadiazole-based donor-acceptor dyes is reported. Using a range of linker units, it is possible to alter the lowest energy transition in terms of intensity (from 8000 to 25000 L mol cm) and wavelength (from 350 to 430 nm). Resonance Raman spectroscopy was used in concert with DFT calculations to indicate that the linker unit participates in charge transfer processes. In each compound the excited state behavior appears to be primarily described by a BTD-Linker-TPA state. Stokes shift versus solvent parameter gradients are on the order of 15000 cm, indicating Δμ values are large. Dual emission is observed in six of the seven compounds and it can be modulated as a function of solvent. TD-DFT calculations, including excited state optimizations (linear response and state specific), indicate that the lowest energy emission is charge transfer in character. The high energy emissive state is assigned as n-π*. In nonpolar solvents, only the low energy charge transfer emission band is observed and this band generally has a high quantum yield (Φ ≈ 0.9). For compounds with phenyl and triazolyl linkers, in polar solvents only the high energy n-π* emission is observed. The high energy n-π* emission has a low quantum yield regardless of solvent.

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A series of donor–acceptor compounds based on triphenylamine and hexaazatrinaphthalene are investigated. Using a variety of linker units, it is possible to tune the intensity of the low‐energy transition from 8 000 m−1 cm−1 to 24 000 m−1 cm−1 and vary the wavelength between λ=430 to 490 nm. The effect of the linker may be observed in the resonance Raman spectra with linker unit modes showing strong enhancement when they are coupled to the charge‐transfer transition. This is evident in the case of the C≡C and triazolyl linker units. Charge transfer is consistent with DFT calculations, which implicate some linkers as having pseudo‐donor‐like behaviour. The emission spectra of the dyes are solvatochromic with Stokes shift versus solvent parameter gradients of 20 000 cm−1, showing that the dipole change is still large even when the bridge becomes involved in the transition.