Multicomponent systems and functional nanocrystals as brightly luminescent probes
Paola Ceroni
Department of Chemistry “G. Ciamician”, University of Bologna, Via Selmi 2, 40126 Bologna,
Italy
paola.ceroni@unibo.it
Abstract
An antenna for light harvesting is an organized multicomponent system in which many
chromophoric molecular units absorb the incident light and then channel the excitation energy
to a common acceptor component. Two different approaches will be discussed in the following:
(i) a multichromophoric system coupling a trimetallic nitride template endohedral
metallofullerene (Y3N@C80) linked to two oligo(phenyleneethynylene) arms (OPE) [1] and (ii)
a family of Silicon nanocrystals (SiNCs) functionalised by organic chromophores.
The first system exhibits the Y3N@C80 emission at 740 nm sensitised by the OPE arms with
unitary efficiency. The emitting excited state is extremely long-lived (16 μs at 298 K) and is
highly sensitive to the presence of dioxygen in fluid solution. The grafting of the OPE units,
exhibiting both liquid-crystalline and absorbing properties, onto the fullerene promotes
mesomorphism in the fullerene adducts where the luminescence properties are retained.
The second approach is based on Silicon nanocrystals that, in the quantum size range (2-12 nm),
can be made as viable light emitters with emission wavelength that can be tuned from the nearinfrared (NIR) into the visible by decreasing their size [2]. Covalent Si-to-carbon bonding also
offers the possibility of integrating inorganic and organic components into robust structures.
The synthesis of luminescent colloidal nanocrystals of silicon is still a difficult task in terms of
reliability and reproducibility. We report the thermal decomposition of hydrogen silsequioxane,
followed by etching and hydrosilylation [3]. This method isolated SiNCs with good yields, high
surface coverage and exceptional control over the dimensions and optical properties of the
materials. In the present work, the H-terminated nanocrystals were used as a platform for copassivation with dodecene and different organic chromophores by thermal hydrosilylation. For
example, we functionalised two families of SiNC of average diameter of 2.5 and 5 nm with
pyrene chromophores: pyrene excitation results in a very efficient (> 95%) energy transfer to
the nanocrystal core (see Figure). To the best of our knowledge this is the first time in which
highly efficient light harvesting from photoactive units to the silicon core have been
demonstrated. This approach enabled us to circumvent the drawback of the low molar
absorption coefficient of SiNCs. The investigated hybrid material exhibits high quantum yield
(40%) also in the NIR spectral region with lifetime in the µs range.
References
[1] K. Toth, J. K. Molloy, M. Matta, B. Heinrich, D. Guillon, G. Bergamini, F. Zerbetto, B.
Donnio, P. Ceroni, D. Felder-Flesch, Angew. Chem. Int. Ed. 2013, 52, 12303 –12307.
[2] J. A. Kelly, E. J. Hendersonw, J. G. C. Veinot, Chem. Commun. 2010, 46, 8704–8718
[3] C. M. Hessel, D. Reid, M. G. Panthani, M. R. Rasch, B. W. Goodfellow, J. Wei, H. Fujii, V.
Akhavan, B. A. Korgel, Chem. Mater.2012, 24, 393−401.