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Research

As part of the Photochemical Nanosciences Laboratory, established by Vincenzo Balzani, the research activity of the group is focused on photoactive supramolecular systems and nanoparticles. Quantum dots, dendrimers and luminescent or photochromic species are investigated for energy conversion (luminescent solar concentrators, artificial photosynthesis and photocatalysis), as well as imaging and photocontrolled nanostructures.

1.   Silicon nanocrystals for energy conversion and imaging

Light-harvesting antennae, constituted by silicon nanocrystals (SiNCs) covalently functionalized at their surface with chromophores display strong, tunable and long-lived (microsecond time-scale) luminescence, insensitive to dioxygen (PhysChemChemPhys 2017, 19, 26507 – 26526). 
This research is funded by an ERC Starting Grant (PhotoSi) and ERC Proof of Concept (SiNbioSys) with two applications:

1.1  light-to-electrical energy conversion

by luminescent solar concentrators (LSC) taking advantage of the apparent large Stokes shift of SiNCs, which absorb in the UV and emit in the red (diameter ca. 3 nm) to near-infrared (diameter ca. 5 nm) spectral region.

 

1.2  bioimaging

by time-gated detection, taking advantage of the long-lived emission of SiNCs. A step further is represented by the use of 2-photon absorbing chromophores integrated in SiNC light-harvesting antenna (Chem 2017, 2, 550 – 560).

2. Photocatalysis and artificial photosynthesis

Photocatalytic processes can not only change reaction rates, but also modify chemical equilibria and, particularly, convert light into chemical energy (Angew. Chem. Int. Ed. 2015, 54, 11320–11337). Our attention is devoted to the design of the photocatalysts for two main applications:

2.1 conversion of light into chemicals

via photocatalyzed organic reactions. The aim of this research is: (i) the design of photocatalyst that are strong light-absorber in the visible region, photostable and with proper redox properties and (ii) the understanding and optimization of the photocatalytic mechanism. A recent example is the use of [Fe(bpy)3]2+ as photocatalyst instead of the most-commonly used [Ru(bpy)3]2+ (ACS Catal. 2015, 5, 5927–5931). 
This research is funded by an ITN grant (PhotoTrain, PI: Prof. Giacomo Bergamini)

 

2.2  conversion of solar light into fuels (artificial photosynthesis)

from widely available raw materials, as H2O and CO2. Light-harvesting antennae based on multichromophoric dendrimers are used as photocatalysts for H2 production in combination with Pt nanoparticle (J. Phys. Chem. Lett. 2014, 5, 798-803), or for energy upconversion by sensitized triplet-triplet annihilation (Chem. Eur. J. 2011, 17, 9560).
This research is funded by a Bilateral Italian-Japanese project and, previously, by national PRIN and FIRB projects.

3.     Organic chromophores for Aggregation Induced Emission (AIE)

The hexathiobenzene core is not luminescent in fluid solution and becomes strongly phosphorescent (Fem ca. 1) in rigid media at room temperature (AIE chromophore, J. Mater. Chem. C 2013, 1, 2717).
Materials displaying room temperature phosphorescence hold promises as OLED emitters and sensors with time-gated detection. In a recent example, the hexathiobenzene group is functionalized by 6 terpyridine units:  upon complexation of Mg2+ cations, a supramolecular polymer is formed and a strong phosphorescence is visible by naked eyes. The system performs as a sensor of Mg2+ cations and a very efficient light-harvesting antenna, which can be disassembled upon addition of fluoride anions (J. Am. Chem. Soc. 2014, 136, 6395). 
This research is funded by the Italian-French University (PhD in cotutelle with Prof. Marc Gingras, Marseille).

4.     Photocontrolled nanocontainers

Photochromic units, such as azobenzene, can be incorporated into multichromophoric systems to make them light-responsive. The dendrimer displayed in the figure perform 3 different functions (J. Am. Chem. Soc. 2012, 134, 15277):
- azobenzene reversible photoswitching
- light-harvesting antenna by naphthalene chromophores
- metal ion coordination by the two cyclam units
These functions can cooperate or interfere depending on the nature of the metal ion: Zn(II) complexes exhibit up to 100% energy transfer from naphthalene to azobenzene, while Cu(II) complexes shut down energy transfer