Computational Design, Synthesis, and Mechanochromic Properties of New Thiophene‐Based π‐Conjugated Chromophores

Abstract

The possibility of exploiting supramolecular architectures for the preparation of innovative mechanochromic devices has been extended by designing novel thienyl-substituted 1,4-bis(ethynyl)benzene dyes, which are characterized by a conjugated, rigid, rodlike core structure. This new family of chromophores was synthesized according to a simple two-step sequential cross-coupling reaction, and the optical properties were investigated in solution and in a polymeric matrix. To tune the mechanochromic performances in smart polymer materials, a virtual screening was set up that was able to select a derivative with optimal spectral features. The effective combination of experimental and computational investigations allowed us to spot those homologues with already potential anisotropic and aggregachromic features and characterized by the best spectral properties and luminescent response. The best candidate was synthesized and dispersed into a polyethylene matrix, indeed achieving an "in silico designed" mechanochromic material. Besides the specific applications of this novel material, the integration of computational and experimental techniques reported here defines an efficient protocol that can be applied to make a selection among similar dye candidates, which constitute the essential responsive part of such supramolecular devices.

Absorption and Emission Spectra of a Flexible Dye in Solution: A Computational Time-Dependent Approach

“…The present work suggests that the selection of the most suitable combination in the TDDFT calculations of the spectral properties should be driven by the comparison of the experimental spectra with broadened theoretical lines, rather than by single point vertical excitations. According to the more or less flexible structure of the target dye and/or to the strenght of the interactions with the surrounding medium, this can be done in a time independent fashion, by accounting for the vibronic structure, 27 or through a time-dependent statistical approach, as done in the present work.…”

“…19,23 In order to reproduce the overall line shapes and their complex features and to reach a more reliable comparison with experimental observations, it is mandatory to take nuclear motions (both of the chromophore and of its environment) into the proper account. [23][24][25][26][27] In the case of flexible molecules in condensed phases, some sampling of large parts of the potential energy surfaces (PES) becomes mandatory 5,15,[28][29][30] and the most suitable approach is based, in our opinion, on molecular dynamics (MD) simulations followed by proper averaging (and smoothing) of TDDFT results for a sufficient number of representative snapshots. Implicit solvation methods, such as the Polarizable Continuum Model (PCM 31 ), offer the undeniable advantage of correctly describing the average polarization of the environment and its effect on the chromophore without any explicit sampling of solvent coordinates, but they are, of course, unable to capture specific solvent effects especially in the cybotactic region.…”

Vapochromic features of new luminogens based on julolidine-containing styrene copolymers

“…32 The process of spin inversion is referred to as intersystem crossing (ISC in Figure 1. 2). Since the transition from T1 to the singlet ground state S0 is forbidden, phosphorescence lifetimes are some order of magnitude greater than the fluorescence ones.…”

“…1 Recently, the introduction of luminescent aggregachromic dyes into polymer matrices has been effectively used for the preparation of new chromogenic materials exhibiting the thermomechanical properties of polymers coupled with optical response to visible light. [2][3][4] Indeed, typical so called "commodities polymers" (i.e. consumer polymers) are often characterized by interesting thermal and mechanical properties, but lack any optical response being usually transparent to wavelengths above 200-300 nm.…”

Excitation Dynamics in Hetero‐bichromophoric Calixarene Systems

“…Another single-point calculation on optimized geometries was performed to extract nonelectrostatic free-energy contributions by using the SMD solvation model. [44,[78][79][80] …”