Order matters: a molecular Lego for building single-molecule optical devices
The property of some molecules to absorb light and give color has been exploited by mankind since ancient times. Among these molecules there are natural colorants such as carmine or methylene blue, which have the property of absorbing visible light and emitting only a fraction of its spectrum. In the case of methylene blue, they only emit the blue fraction of visible light, which gives it its particularity as a dye.
This property results from the electronic configuration of these molecules, i.e. the arrangement and energy of their electrons. Most of the organic molecules that surround us and that make up the molecular network of the biosphere do not have these electronic properties and, therefore, are not affected by visible light. This is what allows life to exist under sunlight. The design and synthesis of non-natural molecules or molecular systems capable of interacting with light and producing a measurable effect is a current issue in the field of new materials, and especially in the field of chemistry, as it is the science responsible for building molecules and designing their functions.
The Organic and Biological Chemistry group of the IPNA's Molecular Sciences department, led by researchers David Tejedor and Fernando García Tellado, has developed a new robust, simple and general-purpose methodology for the construction of new molecular systems capable of absorbing and emitting light in different zones of the visible light spectrum. The process allows controlled and rapid access to aromatic architectures that present an electronic system extended in space and connected to each other that not only interacts with visible light, but also allows this interaction to be modulated to obtain different responses and with various technological applications. This new system is based on the molecule of salicylaldehyde, a compound of great interest both in the field of organic chemistry and new materials or biomedicine because it can be easily inserted into functional systems with activity, among others, as optical sensors or photonic markers for the study of biological processes. In this study, the authors have prepared, as a proof of concept, all the possible substitution geometries of the salicylaldehyde ring with aromatic substituents (Ar1, Ar2, Ar3 and Ar4 in the figure), according to the same or different criteria, from a reduced number of starting materials. The 15 synthesized prototypes cover all replacement geometries, from the most obvious of all equal constructions to the most demanding of all different ones. The rich commercial range of starting products allows for the opening up of a wide variety of possible molecular prototypes to multiple designs in a practical and direct way, which in turn is a gateway to new architectures with optical responses in the areas of the visible spectrum of greatest chemical-biological interest.
This work has been financed by the Ministry of Science, Innovation and Universities (MICIIN), the State Research Agency (AEI) and the European Regional Development Fund (Project PGC2018-094503-B-C21). The results of this study have been published in the journal Chemical Communications. Access to this article is open and has been financed by the CSIC through its URICI Unit.
