Mechanochromic Luminescent Tetrathiazolylthiophenes: Evaluating the Role of Intermolecular Interactions through Pressure and Temperature-Dependent Raman Spectroscopy

Abstract

The Raman spectrum of the mechanochromic luminescent tetrathiazolylthiophene has been investigated as a function of pressure and temperature. This study verifies the sensitivity of the Raman spectroscopy as technique to characterize and understand the structural effects causing any mechanochromic changes. Continuous and evident Raman shifts and changes in intensities of the strongest lines in the spectra occur while increasing pressure or lowering temperature. These spectral changes are related with the modulation of intermolecular C-H…N hydrogen bonding previously identified for this system. The Raman bands involved are assigned to collective normal modes associated to the CC bond stretching of the rings and reveal that the modulation of local hydrogen bonding interaction has indeed an effect which has an impact on the whole conjugated structure of the molecule. Pressure-dependent Raman spectra have been also computed by means of periodic density functional theory calculations of the crystal, giving an accurate prediction of the experimental trends.

Dynamic Covalent Properties of a Novel Indolo[3,2‐b]carbazole Diradical

“…The C−C σ‐bond dissociation in the solid state of the cyclophane dimer was attempted by application of external stimuli such as elevated temperature or pressure. To this end, we have used IR and Raman spectroscopies to probe structural effects causing any mechanochromic changes [6, 7, 54, 58] and for the investigation of the diradical character of quinoidal molecules [59, 60] …”

“…The broken equilibrium caused by the electron transfer converts the cyclophane dimer readily to the monomer anion that undergoes the second reversible reduction.R eversely,t he reoxidation of [ICz-CN] À to the neutral diradical restores the equilibrium with the dominant cyclophane dimer.I tw ould have been even more conclusive to conduct the reversible reductiono fi solated diradical ICz-CN in o-dichlorobenzene at 393 K( FiguresS12 and S13) but the experimentals etup for this experiment was not at disposal. used IR and Raman spectroscopies to probe structural effects causing any mechanochromic changes [6,7,54,58] and for the investigation of the diradical character of quinoidal molecules. [59,60] Upon application of mechanical stimuli, that is, grinding of (ICz-CN) 2 powder with am ortar to prepareaKBr pellet for IR spectroscopy (estimated maximum pressure/stressc a.…”

“…The CÀC s-bond dissociation in the solid state of the cyclophane dimer was attempted by applicationo fe xternals timuli such as elevated temperature or pressure. To this end, we have used IR and Raman spectroscopies to probe structural effects causing any mechanochromic changes [6,7,54,58] and for the investigation of the diradical character of quinoidal molecules. [59,60] Upon application of mechanical stimuli, that is, grinding of (ICz-CN) 2 powder with am ortar to prepareaKBr pellet for IR spectroscopy (estimated maximum pressure/stressc a.…”

Untangling the Mechanochromic Properties of Benzothiadiazole-Based Luminescent Polymorphs through Supramolecular Organic Framework Topology

“…The interconversion process between the two polymorphs was followed by FT-Raman spectroscopy (λ exc = 1064 nm). Raman spectroscopy has been demonstrated to be of great utility to analyze π-conjugated systems, providing precise structural information such as π-electrons delocalization degree, − molecular order, − or supramolecular arrangement. − As seen in Figure , an intense band at 1531 cm –1 , which is assigned to a collective C–C/CC stretching vibration, dominates Raman spectra of both polymorphs. In addition, another two intense bands appear at 1612 and 1363 cm –1 , which correspond to C–C/CC stretching vibrations mainly localized on the outer phenyl rings and the BTD unit, respectively (see the theoretical Raman spectrum in Figure S10).…”

Stimuli-Responsive Benzothiadiazole Derivative as a Dopant for Rewritable Polymer Blends

“…Organic single crystals offer an excellent opportunity to investigate the origin of the different light-emitting properties in bulk organic materials, as they provide accurate information on the relative arrangements of neighboring molecules and how molecules interact with each other as well as which are their conformational preferences, factors which will severely affect the macroscopic emission properties. − In this particular case, the lack of single-crystal data for one of the polymorphs does not allow us to determine how the molecules are interacting within the layers or give us information about the dihedral angle between the BTD and the attached phenyl rings; both factors are of great importance in determining the nature of the color changes. However, in an attempt to shed light on the origin of different colors observed and considering the high sensitivity of Raman spectroscopy not only to intramolecular changes but also to intermolecular interactions of π-conjugated molecules, − we have recorded the Raman spectra of both polymorphs using a laser excitation line of 785 nm (out-of-resonance conditions). As shown in Figure , we focused on the spectral region related with the most intense Raman bands (1200–1700 cm –1 ) which are associated with skeletal CC/C–C stretching vibrations of the conjugated backbone.…”