Poster Prize Winner

Synthesis and characterization of [19]-starphene
Paula Angulo-Portugal1, S. Salaverría2, T. Wang3, J. P. Calupitan1, A. Candia4, J. Lobo-Checa4, J. Besteiro5, L. Mateo5, F. García5, D. Pérez5, M. Corso1,3, D. Peña5 and D. G. de Oteyza2,3

1 Centro de Física de Materiales, CSIC-UPV/EHU, San Sebastián, Spain
2 Nanomaterials and Nanotechnology Research Center, CSIC-UNIOVI-PA, El Entrego, Spain
3 Donostia International Physics Center, San Sebastián, Spain
4 Instituto de Nanociencia y Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, Zaragoza, Spain
5 CIQUS, Universidad de Santiago de Compostela, Santiago de Compostela, Spain

Extended acenes are polyaromatic hydrocarbons (PAHs) that show great potential for nanoelectronics applications since they are expected to have a higher diradical character when increasing the number of π-conjugated rings. Starphenes are a family of extended acenes formed by the trimerization of three acenes in a star manner. Until now, the largest starphene obtained by traditional chemistry is [16]-starphene [1]. The synthesis of larger acenes offers a platform to engineer the energy gap and study carbon magnetism in molecules with extended π-conjugation. However, traditional chemistry methods are not sufficient to carry out the synthesis of increasing size acenes. Thus, other techniques such as on-surface synthesis [2] are needed.

In this work we show three different synthetic methods to obtain on Au(111) and Ag(111) the largest star-shaped acene to date, [19]starphene. Structural and electronic characterization of the products was carried out by scanning tunneling microscopy and spectroscopy (STM/STS). While the previous smaller [16]-starphene showed an energy gap of 1.5 eV on Au(111), [19]-starphene shows a 0.9 eV energy gap. This makes it the smallest gap among any reported acenes confirming the decreasing energy gap trend as the conjugation is increased. Density functional theory (DFT) calculations support our experimental results.

Figure 1: a) Synthetic methods on Ag(111) and Au(111). b) STM images of [19]-starphene with a CO functionalized tip. c) Molecular orbital diagram, constant height and constant current dI/dV maps taken on Au(111).

[1] J. Holec et al., Angew. Chem. Int. Ed. 60, 7752–7758 (2021)
[2] D. G. de Oteyza et al., Chem. Rev. 119, 4717–4776 (2019)