Photophysical properties and excited state dynamics of 4,7-dithien-2-yl-2,1,3-benzothiadiazole.

The relationships between the photophysics and structural properties of 4,7-dithien-2-yl-2,1,3-benzothiadiazole as a function of solvent polarity are investigated both experimentally and by computational methods. Stationary fluorescence measurements are consistent with a model envisaging the presence of three types of conformers in equilibrium in the ground state. They are characterized by different relative orientations of the thiophene rings. Due to a low rotational barrier, the sample in solution is characterized by a distribution of relative internal orientations. By applying the Kawski method, we evaluate the average dipole moment of ground and excited states of the three types of conformers. The ground state dipole moments are small and similar for the three types of conformers. On the contrary, dipole moments differ substantially in the excited state. X-ray diffraction of a single crystal confirms the presence of an orientational disorder of thiophene rings. Transient absorption UV-visible spectroscopy experiments allows the identification of the main mechanisms responsible for the large Stokes shift observed in this push-pull molecule. Time dependent spectra provide a picture of the relaxation processes occurring after excitation: the primary step is an internal charge transfer assisted by thiophene ring planarization which occurs on a time scale ranging from 0.88 to 1.3 picoseconds depending on solvent polarity. Moreover, time-resolved fluorescence measurements are consistent with a mechanism involving planarization accompanied by a stabilization of the charge transfer state as observed in polar solvents. In the latter, longer fluorescence lifetimes are observed along with a quantum yield decrease due to the activation of specific non-radiative relaxation channels. The photophysical behavior of 4,7-dithien-2-yl-2,1,3-benzothiadiazole in a solid matrix of polymethyl methacrylate is similar to that observed in solution, but the overall non-radiative process rate is slow with respect to that in the liquid phase. As a consequence, the radiative processes are enhanced giving rise to a fluorescence quantum yield of 90%. Such behavior is consistent with the proposed relaxation model.

Sculpturing patterns of plasmonic silver nanoprisms by means of photocatalytic lithography.

The controlled shaping of nanoparticles' morphology is one of the pillars of nanotechnology. Here, we demonstrate that photocatalytic lithography, a technique already proved to be useful in materials science, can act as a dry etching technique for noble metal nanoparticles. Triangular silver nanoprisms are self-assembled on titanium dioxide films and photocatalytically shaped into discoidal particles upon irradiation with near-UV light. The obtained patterned surfaces show a dramatically different surface-enhanced Raman scattering response, suggesting the utility of our approach for the development of sensors. The photocatalytic nature of the particle shaping is demonstrated and a plausible mechanism drawn by performing photocatalysis in different configurations (direct and remote) and by irradiating in different solvents.

Enhanced energy transport in genetically engineered excitonic networks.

One of the challenges for achieving efficient exciton transport in solar energy conversion systems is precise structural control of the light-harvesting building blocks. Here, we create a tunable material consisting of a connected chromophore network on an ordered biological virus template. Using genetic engineering, we establish a link between the inter-chromophoric distances and emerging transport properties. The combination of spectroscopy measurements and dynamic modelling enables us to elucidate quantum coherent and classical incoherent energy transport at room temperature. Through genetic modifications, we obtain a significant enhancement of exciton diffusion length of about 68% in an intermediate quantum-classical regime.

Mono- and dinuclear complexes of sulfones with the tetrachlorides of group 4.

The reactions of dialkyl sulfones [R(2)SO(2): R = Me, Et, Ph, R(2)=-(CH(2))(4)-] with the metal tetrachlorides of Group 4 [MCl(4): M = Ti, Zr, Hf] give different products mainly depending on the sulfone/M molar ratio. Compounds of formula [M(2)Cl(8)(R(2)SO(2))(2)][M = Ti, R(2)=-(CH(2))(4)-; M = Zr, R = Et, R = Ph] and [MCl(4)(R(2)SO(2))(2)](sulfone/M = 2)[M = Ti, R = Me; M = Zr, R = Me, R = Ph, R(2)=-(CH(2))(4)-; M = Hf, R = Me, R(2)=-(CH(2))(4)-] have been obtained. By X-ray diffraction methods the dinuclear titanium and zirconium adducts, [Ti(2)Cl(8)(mu-sulfolane-O,O')(2)] and [Zr(2)Cl(8)(mu-Ph(2)SO(2)-O,O')(2)] have been established to contain bridging sulfone and hexacoordinated metal centres, while the mononuclear zirconium complex [ZrCl(4)(Me(2)SO(2))(2)] has cis-monodentate sulfones in a slightly distorted octahedral geometry. The reaction between TiCl(4) and sulfolane (tetrahydrothiophene 1,1-dioxide) in SOCl(2) affords the 1:1 adduct independent of the sulfone/Ti molar ratio. Ligand-exchange and inter-conversion between mononuclear and dinuclear species have been observed by NMR, while the spectral features of the SO(2) moiety have been assigned by IR- and Raman spectroscopies.