The Importance of Excellent π–π Interactions in Poly(thiophene)s To Reach a High Third-Order Nonlinear Optical Response

Abstract

Poly­(thiophene)­s have an inherently large third-order nonlinear optical (TONO) response, but applications are not straightforward due to unoptimized materials. Therefore, several structure–property relationships (molar mass, branching, regioregularity) are investigated to unravel which structural modifications give the highest TONO response. Poly­(3-hexylthiophene) with different molar masses, poly­[3-(2-ethylhexyl)­thiophene] with different molar masses, and random copolymers with different degrees of regioregularity are synthesized and measured by UV–vis spectroscopy and the third harmonic scattering technique. Every structural modification that leads to an increase in π–π interactions in poly­(thiophene)­s leads to an increase in the TONO response of the material. Therefore, a material with a high molar mass, an unbranched alkyl side chain, and a high regioregularity degree is preferably tested as a promising TONO material.

Effect of poly(thiophene)s topology on their third-order nonlinear optical response

“…According to the Spano model, P2 possesses stronger π-π interactions. Since previous research demonstrated that excellent π-π interactions give rise to a large TONO response, 46 the larger TONO response of P2 compared to P1 can be explained by the stronger π-π interactions present. However, since the strength of the π-π interactions between P2 and P3 is the same, they cannot be responsible for the difference in TONO response, meaning that the topology is responsible as it is the only varying parameter between P2 and P3.…”

“…Note that the obtained <γ> are in the same range with <γ> obtained from previous research on poly(thiophene)s. This confirms that poly(thiophene)s lead to a high TONO response. 46 For the linear polymers, P1 and P2, P2 shows a higher <γ> as a result of enhanced π-π interactions. While, when the trigonal nonlinear polymer is compared to its linear counterpart P2, the trigonal nonlinear topology does not give a higher <γ>.…”

“…The polymer solution was illuminated with high intensity polarized light Iω, originating from a high-power pulsed laser beam at an incident wavelength of 1300 nm, which is the most favorable excitation laser wavelength for conjugated polymers. 46 Since third-order nonlinear scattering implies that scattering of the output photons occurs at the triple frequency 3ω compared to the incident frequency ω, the intensity of the scattered light I3ω that contributes to the THS signal is detected at one-third of the incident wavelength, implying detection at 433 nm. 42,43 In addition, the measured intensity I3ω originates completely from the polymer aggregates, since the signal coming from the solvents, chloroform and methanol, is negligible.…”

Ordered‐Structure‐Induced Electrochemical Post‐Functionalization of Poly(3‐(2‐ethylhexyl)thiophene)

“…Anodic chlorination is a typical ePF reaction that has been well investigated in our previous studies. [30][31][32][33][34][35] P3EHT is known to exhibit a semicrystalline character, [36][37][38][39] which suggests that the structure of P3EHT can be controlled by changing the film-preparation process. Therefore, P3EHT is a suitable precursor polymer for investigating the effects of the film structure on the efficacy of ePF.…”

Catechol as a Universal Linker for the Synthesis of Hybrid Polyfluorene/Nanoparticle Materials

“…Apart from the well-known applications such as organic photovoltaics 1−3 and polymer organic light-emitting diodes, 4−7 CPs have shown great promise in applications using Faraday rotation 8−10 and second-and third-order nonlinear optics. 11 Nevertheless, the potential of CPs has yet to reach its limit. This is proven by the recent evolution in which the optoelectronic properties and excellent processability of CPs are found to be a perfect match with the high electron mobility and unique photonic properties of inorganic nanoparticles (NPs).…”