Liquid crystalline materials containing pyrimidine rings

ABSTRACT

Liquid crystals with their unique ordered mesophases and anisotropic physical properties, such as optical, magnetic and dielectric anisotropy, have found wide opto-electronic applications, especially liquid crystal displays (LCDs) in digital electronic devices, such as smart phones, tablets, laptops, TVs, etc. Liquid crystals incorporating 2,5-disubstituted pyrimidine rings in their aromatic cores are often used in commercial LCDs. They are also critical building blocks of liquid crystalline organic semiconductors designed for use in novel organic electronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), sensors, etc. This review will focus specifically on pyrimidine-based liquid crystals, such as calamitic, bent, discotic, taper-shaped, small molecules, oligomers and polymers. It will highlight the relationships between molecular structure and liquid crystalline behaviour, i.e. mesomorphism of relevance to organic and opto-electronic applications. It will highlight the development, optimisation and innovation of liquid crystalline materials containing pyrimidine rings, thereby stimulating the potential for new structural design and applications, such as sensors, flexible electronics, 4D printing and subsequently opening up completely new markets for these advanced functional materials.

GRAPHIC ABSTRACT

The electron-withdrawing pyrimidine units containing two nitrogen atoms at C-3 and C-5 positions in six-membered aromatic rings play a vital role in constructing various liquid crystalline materials, such as calamitic, bent, discotic, taper-shaped, photopolymerised, oligomer and polymer, due to the presence of characteristic mesophases and opto-electronic properties compared with the traditional 1,4-phenylene rings. The heterocyclic pyrimidine-based liquid crystals with a reduced-symmetry structure, highly conjugated π-deficient aromatic rings, and good metal coordinating ability are often used as functional mesogens for application in some promising opto-electronic devices such as ferroelectrics, organic semiconductors, and sensors.

KEYWORDS:

• Pyrimidine liquid crystals
• ferroelectrics
• organic semiconductors
• sensor

Disclosure statement

No potential conflict of interest was reported by the author(s).

Abbreviation

Cr, Cr’, Cr1, Cr2:	=	crystalline phase
G:	=	glass state
N:	=	nematic phase
Sm:	=	smectic phase
SmA1:	=	a monolayer smectic A phase
SmAd:	=	a partial bilayer smectic A phase
Col:	=	columnar phase
ColL:	=	lamellar columnar phase
Colh, Colhex:	=	hexagonal columnar phase
Colhd:	=	disordered hexagonal columnar phase
NCol:	=	columnar nematic phase
LamColrec =	=	lamellas-columnar phase with rectangular symmetry
Ch:	=	cholesteric phase
I:	=	isotropic liquid state
IsoX:	=	isotropic X phase
TGB:	=	a filament texture similar to the so-called fingerprint texture
SmCanti:	=	antiferroelectric smectic C phase
SmCalt:	=	alternating smectic C phase
*:	=	chiral mesophase
LC:	=	liquid crystal
NLC:	=	non-liquid crystal

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [62204093 and 22205155], Guangdong Basic and Applied Basic Research Foundation [2021A1515111166], The Natural Science Foundation of Jiangsu Higher Education Institutions of China [22KJB510014 and 22KJB150011], Natural Science Foundation of Jiangsu Province [BK20220640], Huai’An Talent Funding for Outstanding Doctors in Universities [Z302J22518], Natural Science Foundation of Huai’An City [HAB202149], and PhD Research Start-up Fund of Huaiyin Institute of Technology [Z301B19582].