Stimuli-Responsive Molecular Switches and Logic Devices Based on Ru(II)–Terpyridyl–Imidazole Coordination Motif

Abstract

We report herein the synthesis, photophysics, and electrochemistry of three Ru­(II)–terpyridine complexes derived from a new terpyridyl–imidazole ligand (tpy-HImzPh 3 F 2 ) and study their pH- and temperature-responsive behaviors toward the fabrication of molecular switches. The complexes emitted at room temperature (RT) have a lifetime within the 4.5–49.0 ns domain, depending on the auxiliary ligand and the solvent used. In the acidic region, the complexes exhibit emission, indicating the “on-state”, while in the basic condition, the emission is totally quenched, indicating the “off-state”. Similarly, when the temperature is lowered, the emission intensity and lifetime are enhanced, demonstrating the on-state, while increase of temperature leads to quenching of the emission intensity and lifetime, designated as the off-state. In both cases, the process is reversible. The bathochromic shift of the spectral band together with the emission quenching and lowering of the Ru3+/Ru2+ potential is also observed upon deprotonation at elevated pH. In addition, systematic variation of the absorption spectral behaviors upon variation of pH helps in evaluation of the pK a’s of the complexes. In essence, the complexes can act as switches emanated from a huge change in their absorption, emission, and redox behaviors as a function of their acidity/basicity (pH) and temperature. Moreover, their emission spectral responses as a function of pH and temperature were utilized for the fabrication of two-input binary logic gates. Density-functional theory (DFT) and time-dependent density-functional theory (TD-DFT) computations are performed for appropriate interpretation of the spectral bands.

Analysis and prediction of anion- and temperature responsive behaviours of luminescent Ru(ii)-terpyridine complexes by using Boolean, fuzzy logic, artificial neural network and adapted neuro fuzzy inference models

“…Previously, we reported a series of similar Ru( ii ) complexes derived from related terpyridyl-imidazole ligands differing by the terminal NMe 2 motifs and studied their photophysical characteristics as well as anion- and temperature responsive behaviours. 42,43,52 Acid-induced remarkable enhancement of RT emission lifetime (up to 80-fold) of our previously reported methyl-substituted terpyridyl-imidazole based Ru( ii ) complexes actually motivates us to investigate the present system. The enormous increase in the lifetime was ascribed to the protonation of imidazole nitrogen(s) in the second coordination sphere of complexes which was facilitated by the electron donating Me-substituent.…”

“…† By comparing the spectra of the structurally related complexes, the intense absorption peak within 488-512 nm can be assigned as Ru(II) → terpyridine charge transfer transition (MLCT), while the peaks within the domain of 330-350 nm as imidazole → tpy intra-ligand charge transfer (ILCT) transitions. 43,52 The very strong peaks at ∼280 and ∼315 nm are due to π → π* electronic transition within the ligand framework.…”

“…In BL, the output signal varies between two extremes, "0" or "1". [52][53][54][55][56][57][58][59][60][61][62][63] But the practical systems often consist of innumerable intermediate states. To address the in-between states, the FL is an appropriate choice.…”

Anion and Light Responsive Molecular Switches Based on Stilbene‐Appended Ru(II) Terpyridyl‐Imidazole Complexes That Mimic Advanced Boolean and Fuzzy Logic Operations

“…[10][11][12][13][14][15] We noticed that the systems based on metal complexes are relatively less than that of their pure organic precursors in demonstrating complicated logic operations. [16][17][18][19] In the present work, our objective is to use the coordination complexes of Ru 2 + metal based on polyheterocyclic ligands which can mimic advanced and complicated logic functions upon the action of different external stimuli. The interest in polyheterocyclic complexes of Ru(II) arises due to their very rich photophysical and electrochemical behaviors and remarkable photo-stability together with their active involvement in different applications such as in optical devices and sensors.…”

“…A wide variety of molecular systems have been designed which can mimic different binary logic functions upon the action of various activating stimuli such as light, electricity and chemical species [10–15] . We noticed that the systems based on metal complexes are relatively less than that of their pure organic precursors in demonstrating complicated logic operations [16–19] …”