Solvent-Free Conjugated Polymer Fluids with Optical Functions

Abstract

Solvent-free fluidic materials possessing optoelectronic functions are expected to be major components in soft electronics applications. Conjugated polymers are promising targets for this purpose and their design approaches are classified into three types with respect to their structure: conjugation breaking (Type I), copolymerization with flexible polymers (Type II), and side chain engineering (Type III). In this short review, we highlight several early attempts to produce Type III conjugated polymers. We also present fully characterized Type III fluids recently developed by our group, with a brief summary of the structure–property relationship and fluidity-oriented functions.Introduction1 Polymer Design1.1 Fluidity of Polymeric Materials1.2 Type III CPs with T g < 25 °C1.3 Fluidification of Polyfluorenes1.4 Effect of Side Chain Length2 Fluidity-Oriented Functions2.1 Mechanofluorochromism2.2 Consistent Luminescence in Wide Range of Elastic Moduli2.3 Prediction of ViscoelasticityConclusions and Outlook

Organic molecular and polymeric electrets toward soft electronics

“…Similarly to alkylated porphyrin liquid (2), conjugated polymers can be greatly softened by introducing branch alkyl side chains, which can act as an "internal plasticizer". [107][108][109][110] The viscoelasticity of conjugated polymer fluids can be easily adjusted by introducing a bulky of branched alkyl side chains (different alkyl chain length). 109 This softening methodology for conjugated polymers could also be applicable for the development of flexible/stretchable electrets.…”

Stretchable π-conjugated polymer electrets for mechanoelectric generators

“…1a). Branched alkyl chains with a branch at the 2position, the so-called Guerbet chains (C n C n+4 ), are highly capable of softening and amorphizing rigid π-conjugated molecules [26][27][28][29][30] and polymers [25,31,32] and enable a wide range of elastic modulus (G') tunability. P1, with short side chains (n = 2), is a glass at room temperature (T g = 29 °C), while P2, with long side chains (n = 8), is a liquid (T g = −29 °C).…”

Responsive molecular liquid materials

“…[52] A remarkable point in such a molecular design is that the fluidity in a solvent-free liquid state and the strength of the interaction between functional cores can be controlled by the length, the degree of branching, and the substitution position of the flexible molecular chains. [53][54][55][56][57][58][59] For example, in a study using alkylated liquid pyrenes as the model molecule, [60] when only one side of the pyrene core was modified with alkyl chains so that the pyrene core was not fully covered, the luminescence was delivered from the excimer formation between the pyrene cores. In this case, van der Waals and π-π interactions acted between the molecules (Figure 1a).…”

“…It is possible to create molecular liquids with various optical functions by selecting functional π ‐conjugated cores such as those with full‐color luminescence, [37,49] room‐temperature phosphorescence, [50,51] and upconversion [52] . A remarkable point in such a molecular design is that the fluidity in a solvent‐free liquid state and the strength of the interaction between functional cores can be controlled by the length, the degree of branching, and the substitution position of the flexible molecular chains [53–59] . For example, in a study using alkylated liquid pyrenes as the model molecule, [60] when only one side of the pyrene core was modified with alkyl chains so that the pyrene core was not fully covered, the luminescence was delivered from the excimer formation between the pyrene cores.…”