Photophysics of hydrogen bonded diarylethene dimers in the liquid phase

Is energy transfer limiting multiphotochromism? answers from ab initio quantifications

Dithienylethenes (DTEs) can be assembled to form supramolecular multiphotochromic systems that are highly functional molecular architectures of potential interest for building complex optoelectronic devices. Yet even simple DTE dimers relying on an organic linker may suffer from a partial photoactivity, i.e., only one of the two switches does isomerise. Experimentally, this limited photochromism has been attributed to an excited state energy transfer (EET) between the two DTEs of the multimer; this EET taking place instead of the desired photoinduced cyclisation of the DTE. However, no clear evidences of this phenomenon have been provided so far. In this work we propose the first rationalisation of this potential parasite photoinduced event using a computational approach based on Time-Dependent Density Functional Theory (TD-DFT) for the calculation of the electronic coupling in DTE dimers. Besides quantifying EET in several systems, we dissect the role of through-bond and through-space mechanisms on this process and clarify their dependence on both the nature and length of the bridge separating the two photochromes. The theoretical data obtained in this framework are in full agreement with the experimental outcomes and pave the way toward a molecular design of coupled, yet fully functionals, DTE-based multiswitches.

A multi-state fluorescent switch based on a diarylethene with an acridine unit

A new asymmetrical fluorescent diarylethene derivative with an acridine unit was synthesized by Schiff base condensation. The derivative was sensitive to lights and special metal ions. Stimulated by UV/vis lights and Zn²⁺, distinct changes were observed in UV-vis and fluorescent spectra. Upon addition of Zn²⁺, the derivative emission peak was blue-shifted by 34nm and the emission intensity was enhanced by 16 fold, accompanied by the fluorescent color changed from red to light yellow, due to the formation of a 1:1 metal/ligand complex. The complex exhibited excellent fluorescence switching upon irradiation with UV light. Taking advantage of the lights and Zn²⁺ stimuli (inputs), and fluorescence intensity at 580nm (output), a molecular logic gate was constructed. Moreover, a new absorption band centered at 420-450nm emerged upon exposure to Zn²⁺. The dramatic color change of the solution made the 'naked-eyes' detection of Zn²⁺ possible.

Designing efficient photochromic dithienylethene dyads

Aiming at designing more efficient multiphotochromes, we investigate with the help of ab initio tools the impact of the substitution on a series of dimers constituted of two dithienylethene (DTE) moieties, strongly coupled to each other through an ethynyl linker. The electronic structure and the optical properties of a large panel of compounds, substituted on different positions by various types of electroactive groups, have been compared with the aim of designing a dyad in which the three possible isomers (open-open, closed-open, closed-closed) can be reached. We show that appending the reactive carbons atoms of the DTE core with electroactive groups on one of the two photochromes allows cyclisation to be induced on a specific moiety, which leads to the formation of the desired closed-open isomer. Substituting the lateral positions of the thiophene rings provides further control of the topology of the frontier molecular orbitals, so that the electronic transition inducing the second ring closure stands out in the spectrum of the intermediate isomer.

Multiphotochromic molecular systems

We review molecular compounds encompassing several photochromic units with a focus on their functionalities.