Effects of Mechanical Stretching on the Properties of Conjugated Polymers: Case Study for MEH‐PPV and P3HT Oligomers

Abstract

Nowadays, the development of new materials for applications in flexible optoelectronic devices is one of the main frontiers of science. However, in order to improve the applicability and durability of such devices, a deeper understanding of the effects induced by mechanical deformations on the properties of their components is still necessary. In this sense, in the present study, it is evaluated the effect of mechanical stretching in the structural, electronic, and optical responses of two widely investigated organic polymers with great technological interest: poly(2-methoxy,5-(2 0ethylhexyloxy)-1,4-phenylene vinylene) and poly(3-hexylthiophene-2,5-diyl). Hartree-Fock and density functional theory electronic structure calculation methods were employed for the study of oligomeric structures subjected to increasing stretch levels along the polymerization axis. The results show a dependence of the polymer properties with the mechanical deformation, allowing to identify distinct response regimes according to the main chain stretching. In particular, it is noticed that large stretches lead to nonfunctional devices, mainly due to the localization of the frontier orbitals and degradation of optoelectronic properties. In addition, it was also identified that very small deformations can lead to some interesting optoelectronic responses, which could indicate an alternative route for the design of organic devices via mechanical processes.

Conception and Theoretical Study of a New Copolymer Based on MEH-PPV and P3HT: Enhancement of the Optoelectronic Properties for Organic Photovoltaic Cells

“…The structures of the basic homopolymers and their derived copolymers were modeled using the density functional theory (DFT) [ 14 , 15 ]. The geometric optimization was carried out using the functional hybrid B3LYP method [ 16 , 17 , 18 ] and the base set 6-31G (d, p) [ 19 ].…”

Influence of Air Flow on Luminescence Quenching in Polymer Films towards Explosives Detection Using Drones

“…In this section, we discuss the bandgap energies and the PL spectra of PEE polymer. The electronic delocalization of conjugated polymers was discussed earlier [ 29 , 30 , 31 ], and HOMO LUMO levels were calculated by Density Functional Theory (DFT) simulations for some conjugated polymers [ 32 , 33 ]. In Figure 2 a, we show the HOMO and LUMO energy levels and bandgap energies of the PEE polymer obtained from DFT simulations (Orca 4.2.0) using the B3LYP method with a 6-31G basis function.…”

Effects of Mechanical Deformation on the Opto-Electronic Responses, Reactivity, and Performance of Conjugated Polymers: A DFT Study

“…Ten transitions were evaluated, considering only single excitations. The exciton binding energies ( E X ) (Equation (2)) were estimated from the difference between the fundamental gaps (from KS-FMOs) and the vertical transition energies ( E vert ) resulting from TD-DFT calculations [ 41 , 76 , 77 ]. …”

“…In this context, molecular modeling techniques can be considered relevant tools to evaluate the variety of mechano-responsive processes, particularly to identify factors associated with the degradation of the optoelectronic properties, propose alternatives for their minimization, and guide the development of new materials with improved responses [ 41 ]. Such analyses are especially interesting for polymeric devices due to their high degree of structural flexibility and the strong relationship between conformational and optoelectronic properties [ 25 , 34 , 41 , 42 ].…”

“…Despite this, there is a scarcity of theoretical works on the effect of mechanical deformations on the optoelectronic properties of semiconducting polymers. Our previous studies at a moderate level of theory (semiempirical + density functional theory (DFT)) indicated that mechanical elongations of MEH-PPV and P3HT polymer chains lead to deleterious effects on the optoelectronic responses of the materials, which occurs at different regimes and levels [ 41 ]. However, the limitations imposed by the use of semiempirical approximations (for geometry optimization), and the observation of strong steric effects of the side groups, deserve further study.…”