Journal Name COMMUNICATION This journal is © The Royal Society of Chemistry 20xx J. Name ., 2013, 00 , 1-3 | 1 Please do not adjust margins Please do not adjust margins Received 00th January 20xx, Accepted 00th January 20xx DOI: 10.1039/x0xx00000x www.rsc.org/ Aggregation-induced emission of [3]cumulenes functionalized with heptagon-containing polyphenylenes Vicente G. Jiménez, a Rubén Tapia, a Miguel A. Medel, a Inês F. A. Mariz, b Tânia Ribeiro, b Victor Blanco, a Juan M. Cuerva, a Ermelinda Maçôas b and Araceli G. Campaña* a Lighting on the fluorescence of [3]cumulenes: we report the luminiscence at room temperature by aggregate formation of [3]cumulenes functionalized with propeller-like heptagon- containing polyphenylenes. These endgroups turn on the emission of a [3]cumulene by steric protection and restriction of their intramolecular rotations in the aggregates. [n]Cumulenes, organic molecules with n double bonds in a contiguous sequence, have attracted increasing interest in recent years as promising model compounds for the understanding of carbyne. 1 In comparison to other related conjugated molecules as polyenes or polyynes, [n]cumulenes are more reactive and therefore less stable. Nevertheless, extraordinary synthetic efforts have been made and thus the structural and electronic properties of [3] to [9]cumulenes have been studied by X-ray crystallography and UV-Vis absorption spectroscopy. 2 However, photoluminescence properties of [n]cumulenes remain almost unexplored. 3 As planar conjugated systems, [n]cumulenes tend to easily aggregate leading to the quenching of their emission. Aggregation-caused quenching (ACQ) is a general effect of conventional π-conjugated chromophores which limits their applications in biological aqueous media or as solids or films. In contrast to ACQ, the alternative phenomenon of aggregation-induced emission (AIE) has received major attention since B. Z. Tang et. al. described it in 2001 4 and extensive progress and many applications have been reported. 5 Typical examples of structural motifs present in AIE-active molecules are hexaphenylsilole (HPS) or tetraphenylethene (TPE, Chart 1). 6 As AIE-luminogens, both compounds are non-emissive in solution, as solvation allows the rotation of their phenyl rings which dissipates their excited- state energy by a non-radiative deactivation. In contrast, their emission is activated upon aggregation due to the restriction of the intramolecular motion (RIM) of the phenyl rings resulting in slower non-radiative decay rates and higher fluorescence emission yields. We envisioned that the introduction of adequate endgroups could turn on the emission of [3]cumulenes at room temperature in polar media as a result of an AIE phenomenon. Hence, herein we report that the steric protection of the [3]cumulene fluorophore by propeller-like heptagon-containing polyphenylenes as endgroups turns on its emission upon aggregation (Chart 1, compound 1). In addition, we show the two-photon based upconversion of the [3]cumulene 1- aggregates. This strategy opens up the possibility of using [n]cumulenes as active luminogens upon aggregation. Chart 1 Compounds studied as AIE-emitters: [3]cumulene derivatives 1-4 and tetraphenylbutatriene (TPBT). Related previously reported AIE-luminogens tetraphenylethene (TPE) 6b and 5,5’-dibenzo[a,d][7]annulenylidene (BDBA) 10 . a. Departamento de Química Orgánica. Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain. b. Centro de Química Estructural and Institute of Nanoscience and Nanotechnology (IN), Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal. Electronic Supplementary Information (ESI) available: General details, synthesis and spectroscopy data. Experimental details on optical measurements. Crystal data and structure refinement of compounds 1, 3, 8 and TPBT. CCDC 1817320-1817323. Further details on theoretical calculations and Cartesian coordinates of computed structures. See DOI: 10.1039/x0xx00000x