Three benzimidazole-based isomers bHBI, bHBI-mL, and bHBI-pL were synthesized by introducing a benzonitrile group at the N1 position, and the substituent positionally isomeric 2’-hydroxyphenyl (phenolic ring) at the C2 position. Their fluorescence emission behaviors in solution and solid state were investigated. The results revealed that the introduction and positional isomerism of N,N-diethyl groups on the phenolic ring significantly influenced their fluorescence properties. In solution, bHBI-mL exhibited a positive solvatochromic effect in emission wavelength and fluorescence quenching in protic solvents. In contrast, bHBI showed a slight blue shift in emission wavelength with increasing solvent polarity, while bHBI-pL underwent quenching across solvents of varying polarities. In crystalline state, the fluorescence behaviors were governed by the N,N-diethyl group introduction and positional isomerism, which dramatically altered molecular dipole moments and packing modes. The bHBI and bHBI-mL crystals emitted green and cyan fluorescence, respectively, with minor emission wavelength shifts after grinding. The fluorescence of bHBI was originated from a stable conformational isomer featuring an intramolecular hydrogen bond between enol-like and keto-like forms. Remarkably, bHBI-pL crystals displayed high-contrast color changes (dark red to bright orange) and distinct “on-off-on” fluorescence switching characteristics upon grinding. Its crystalline fluorescence arose from dark-state TICT (twisted intramolecular charge transfer) emission, while grinding induced planarization of molecular configuration, leading to dramatically enhanced fluorescence intensity. These high-contrast fluorescent molecules have great potential for applications in the fields of anti-counterfeiting packaging and more.