Optimizing bidirectional “highway” for photoactive response through guanidine-chromophore junction
Guanidine moiety has been used in enzymes and synthetic receptors for binding different anions and anionic substrates. Moreover, different chromophores have been incorporated into guanidine receptors to provide additional functionality, which allows these hosts to act as colorimetric or fluorescence probes. In order to extend the functionality of such molecules to photo-switches and logical circuits of photo-optical devices, a deeper understanding of guanidine-chromophore interactions is highly desirable. Therefore, anion-guanidine-chromophore (AGC) junctions will be thoroughly investigated by means of theoretical methods especially tailored for excited-state description. Particular attention will be given to the possibility of information transfer between the anion and the chromophore through the guanidine or guanidinium moiety in both directions of the junction. Firstly, the conditions under which the anion binding can cause prominent change in the chromophore’s absorption or florescence spectra will be investigated. In other words, we will determine the conditions to maximize the transfer of chemical signal between the anion and the chromophore through the guanidine moiety. The effect of the bound anions on the absorption spectrum of a large collection of chromophores will be determined. Based on this information, the most sensitive chromophores will be pinpointed and their usage as anion-sensing reagents will be suggested and forwarded to experimentalists for future anion selectivity tests. A second research line will consider the photoactivation of the chromophore to transfer the signal in the opposite direction through the guanidine “highway”. In this case, the transfer of photo-energy to guanidinium moiety through two-hole – one-particle states, expected for protonated forms, should be followed by subsequent guanidine-anion photodissociation. The goal is to determine the conditions for light-controlled anion releasing for guanidine-based ion carriers, including molecular transporters through membranes.