Solvent‐Free Luminous Molecular Liquids

Abstract

Solvent‐free luminous molecular liquids (LMLs) are a new generation of soft matter which exhibit uncharged, nonvolatile, and fluidic nature and emit intense and homogeneous luminescence in the condensed state. They can be produced readily on the gram scale by modifying luminophores with bulky, flexible, and low‐melting side chains. Their performance can be facilely enriched by blending them with commercially available functional substances. Therefore, since their active optoelectronic properties were perceived a decade ago, LMLs have been regarded as promising contributing components in the burgeoning field of flexible and wearable light‐emitting devices. Recently, richer insights into LMLs have triggered various new applications. Additionally, unexpected phase behavior and photophysical properties have been discovered coincidentally. Therefore, the sensible and sophisticated molecular design principles of LMLs are still being augmented to guarantee predictable, steady, and consistent end‐use performance. This review summarizes the latest developments in LMLs, including molecular design principles, regulation and enrichment of their photophysical properties, and their versatile applications. Additionally, a prediction of the perspectives of LMLs in the near future is presented at the end.

Entropic Mixing Allows Monomeric‐Like Absorption in Neat BODIPY Films

“…Strong intermolecular interactions are extremely sensitive on relative distances and orientations, and the most widely adopted method of reducing these interactions are by adding large bulky substituents to the chromophore core [6] . These substituents, whose van der Waal interactions are known to interplay with the π–π interactions of the chromophore cores, enclose the chromophores, insulating it from the environment, and thereby enable unperturbed photophysical properties in neat films [6b, 7] . However, substituents are often much larger than the chromophore itself, causing an effective concentration decrease, limiting the method to applications where the concentration and intermolecular communication is less important [8] …”

Solid‐State Low‐Temperature Thermoresponsive and Reversible Color Changes of Conjugated Polymer in Layered Structure: Beyond Infrared Thermography

“…For example, liquid‐state conjugated polymers have been developed in recent years. [ 23,24 ] Here, we use a layered structure with tunable flexibility to induce motion of conjugated polymers in solid state in a low‐temperature range of around 100 K.…”

Ionic Charge-Transfer Liquid Crystals Formed by Alternating Supramolecular Copolymerization of Liquid π-Donors and TCNQ

“…The room-temperature π-liquid became widely known for octyl methoxycinnamate, which has been utilized as an ultraviolet absorbing agent over several decades (Marti-Mestres et al, 2000 ; Scalia and Mezzena, 2010 ). It was popularized by the development of liquid chromophores containing carbazole (Hendrickx et al, 1999 ; Hirata et al, 2011 ), anthracene (Babu et al, 2013 ; Duan et al, 2013 ), oligo ( p -phenylene vinylene) (Babu et al, 2012 ), azobenzene (Masutani et al, 2014 ), and so forth (Snaith et al, 2006 ; Kamino et al, 2012 ; Li et al, 2013 ; Takeda et al, 2018 ; Ghosh et al, 2019 ; Isoda et al, 2019 ; Lu and Nakanishi, 2019 ; Ogoshi et al, 2019 ; Morikawa et al, 2020 ; Bai et al, 2021 ). These π-liquids have been utilized as liquid semiconductors (Hendrickx et al, 1999 ; Snaith et al, 2006 ; Hirata et al, 2011 ; Kamino et al, 2012 ; Li et al, 2013 ), solvent-free luminescent liquids (Babu et al, 2012 , 2013 ; Lu and Nakanishi, 2019 ; Bai et al, 2021 ), stimuli-responsive liquid (Takeda et al, 2018 ; Isoda et al, 2019 ; Ogoshi et al, 2019 ), liquid electret (Ghosh et al, 2019 ), photon upconverters (Duan et al, 2013 ), and solar thermal fuels (Masutani et al, 2014 ; Morikawa et al, 2020 ).…”

“…These π-liquids have been utilized as liquid semiconductors (Hendrickx et al, 1999 ; Snaith et al, 2006 ; Hirata et al, 2011 ; Kamino et al, 2012 ; Li et al, 2013 ), solvent-free luminescent liquids (Babu et al, 2012 , 2013 ; Lu and Nakanishi, 2019 ; Bai et al, 2021 ), stimuli-responsive liquid (Takeda et al, 2018 ; Isoda et al, 2019 ; Ogoshi et al, 2019 ), liquid electret (Ghosh et al, 2019 ), photon upconverters (Duan et al, 2013 ), and solar thermal fuels (Masutani et al, 2014 ; Morikawa et al, 2020 ). Although some π-conjugated organic liquids reported to date show electron-donating or accepting properties, they are categorized as weak donors or acceptors (Babu and Nakanishi, 2013 ; Lu and Nakanishi, 2019 ). The CT complexes are classified by the degree of CT (ρ CT ), where ρ CT = 0 for neutral TCNQ and ρ CT = 1 for complete charge transfer as found for K-TCNQ (Chappell et al, 1981 ).…”