Acenes are polycyclic aromatic hydrocarbons (PAHs) consisting of linearly fused benzene rings. In the recent past, acenes have been of interest from fundamental and applied perspectives. Smaller acenes such as benzene, naphthalene, and anthracene are among the most studied organic compounds and their properties are well explored. Pentacene has received considerable attention as the most promising active semiconductor for use in organic thin film transistors (TFT) because of its high charge-carrier mobility; however, poor environmental stability is one of the problems limiting its practical application. As the number of rings increases, the members of the acene family become increasingly reactive.
The successful synthesis of heptacene developed by Mondal et al used the Strating-Zwanenberg photodecarbonylation reaction. The lesser stability of the tetracene moieties in the nonacene photoprecursor compared to the anthracene moieties of the heptacene process make its synthesis more challenging. The latter scheme requires 2,3-dibromoanthracene as one of the starting materials. Besides the poor solubility of 2,3-dibromoanthracene, failure was also due to insufficient formation of anthracyne upon treatment of 2,3-dibromoanthracene with n-BuLi. Although the initial idea didn't work we used the same scheme replacing 2,3-dibromoanthracene with 7,8-dibromo-1,4-dihydroanthracene. The reaction of the latter with 5,6,7,8-tetramethylenebicyclo[2.2.2]oct-2-ene gave 1,4,7,8,9,12,15,18,19,20-octadecahydro-8,19-diethenononacene albeit in low yield. Multiple attempts to dehydrogenate the non-aromatic rings using DDQ and other reagents under various conditions failed to produce the desired compound.
Recently Miller reported the synthesis of relatively stable heptacene derivatives having a combination of arylthio and o-dialkylphenyl substituents. Miller's scheme used 1,2,4,5-tetrakis(bromomethyl)-3,6-bis(4'-t-butylthiophenyl)benzene as the core precursor. Another synthetic approach has been undertaken that employs Miller's 1,2,4,5-tetrakis(bromomethyl)-3,6-bis(4'-t-butylthiophenyl)benzene in its core. First attempts to react the latter with 1,4-anthraquinone to produce nine linearly fused ring system were unsuccessful. Interestingly in both approaches we used, a dienophile benzyne-type and quinone-like with more than one fused ring were unreactive in subsequent Diels-Alder reactions. So similarly to the prior scheme, a dienophile with terminal nonaromatic ring (6,7,8,9-tetrahydro-1,4-anthraquinone) was used along with 1,2,4,5-tetrakis(bromomethyl)-3,6-bis(4'-t-butylthiophenyl)benzene to yield a nine-ring backbone structure which was treated with mesityl magnesium bromide followed by reduction to yield 1,2,3,4,12,13,14,15-Octahydro-8,19-bis(4'-t-butylphenylthio)nonacene. Unfortunately this compound wasn't isolated or properly characterized.
Combining metal and semiconductor domains in a single nanocrystal offer a unique opportunity for the development of hybrid nanoscale composites with functionalities that extend beyond those of isolated materials. The presence of powerful carrier confinement in these nanoparticles joint with tunable geometry of the semiconductor-metal interface gives rise to novel optoelectronic properties that can potentially add up to a wide range of applications. Recently, Au/CdS and Au/CdSe heterostructures containing gold domains grown onto cadmium chalcogenide semiconductor nanorods (NRs) have come forward as a model system for studying such hybrid nanomaterials.
In this work we have developed several chemical routes to CdSe/CdS core-shell nanocrystals (NCs) with each of them leading to different shape of nanocrystals. Also a simple chemical method for growing Au domains onto CdS nanorods and CdSe/CdS NCs in oleylamine was developed. The size of Au NCs can be precisely tuned by adjusting the temperature of the reaction mixture, while the shape of Au/CdS nano-composites (matchstick or barbells) is controllable via the reaction rate. All of the aforementioned nanocomposites had semiconductor emission quenched and further study is necessary to determine whether a significantly wider band gap shell material can prevent fast transfer of excited carriers from semiconductor into metal domains.