Partial Photopolymerization of Fantrip on Calcite (10.4)

Abstract

On-surface synthesis has emerged as a fascinating route for creating functional molecular architectures on surfaces that may not be accessible by solution chemistry. An impressive variety of different structures have been achieved by exploiting various synthesis routes, including thermally as well as photochemically induced reactions. While it has been demonstrated that the substrate can influence the reaction pathway, the majority of studies presented so far are limited to electrically conducting substrate materials. Here, we present an atomic force microscopy study of the structure formed by fluorinated anthracene triptycene (fantrip) deposited onto the bulk insulator calcite (10.4) kept in ultrahigh vacuum. We compared the structures before and after irradiation with UV light. Before irradiation, fantrip self-assembles into a hexagonal structure, which represents the starting configuration for the subsequent topochemical [4 + 4] photopolymerization. On graphite, this starting configuration has earlier only been obtained after passivating the substrate. A detailed analysis of the irradiated network obtained here reveals a tendency toward direction-dependent linking. Compared with the network formed on a passivated graphite surface, in the present case, the network size remains limited. This could be ascribed to the kinetically hindered mobility of the molecules on the surface, hampering the formation of an ideal arrangement for topochemical reaction. Our study provides evidence for partial photopolymerization, as reflected in the directional dependence, thereby highlighting the pivotal importance of the substrate in the on-surface synthesis.