Optical film having a liquid crystal layer including twisted nematic liquid crystal compounds

An optical film comprising a twisted nematic (TN) liquid crystal layer, the TN liquid crystal layer comprising:

• nematic liquid crystal compounds twisted along a virtual helical axis aligned in the TN liquid crystal layer and polymerized in a TN aligned state such that the helical axis is parallel to a thickness direction of the TN liquid crystal layer, and of the following Formula 1, and an angle between an optical axis of the nematic liquid crystal compounds present in the lowermost part of the TN layer and an optical axis of the nematic liquid crystal compounds present in the uppermost part of the TN layer is in a range from 50 to 300 degrees, and the layer does not include any cholesteric liquid crystal compounds having a twist angle of 360 degrees;
• and
• a chiral agent forming a concentration gradient along a thickness direction of the liquid crystal layer, wherein a rotation angle of the liquid crystal compound variably changes in the thickness direction so that a change of an angle between the optical axis of the liquid crystal compound at the lowermost part of the TN liquid crystal layer and the optical axis of the liquid crystal compound according to a thickness is not constant,
• wherein:
• the liquid crystal layer exhibits a reverse-wavelength dispersion and satisfies the following Expression 1:
• Expression 1
• R(650)/R(550)>R(550)/R(550)>R(450)/R(550)
• where R(650) is an in-plane retardation value of the TN liquid crystal layer with respect to light with a wavelength of 650 nm, R(550) is an in-plane retardation value of the TN liquid crystal layer with respect to light with a wavelength of 550 nm, and R(450) is an in-plane retardation value of the TN liquid crystal layer with respect to light with a wavelength of 450 nm,
• wherein in Formula 1, A is a single bond, —COO—, or —OCO—, and R1 to R10 are independently hydrogen, a halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group, —O-Q-P, or a substituent of the following Formula 2, respectively, and at least one of R1 to R10 is —O-Q-P or a substituent of the following Formula 2, where Q is an alkylene group or an alkylidene group, and P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group, or a methacryloyloxy group,
• wherein in Formula 2, B is a single bond, —COO—, or —OCO—, and R11 to R15 are each independently hydrogen, a halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group, or —O-Q-P, and at least one of R11 to R15 is —O-Q-P, where Q is an alkylene group or an alkylidene group, and P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group, or a methacryloyloxy group.