An efficient fluorescent Cr³⁺ receptor, 2-(5,6-dihydro-benzo-[4,5]imidazo[1,2-c]quinazolin-6-yl)-quinolin-8-ol (H₂L¹) was synthesized and characterized by physico–chemico and spectroscopic tools along with single crystal X-ray crystallography. This probe (H₂L¹) behaves as a highly selective fluorescent sensor for Cr³⁺ ions at biological pH in ethanol–water (1 : 5, v/v) HEPES buffer (0.1 M, pH 7.4) at 27 °C. Metal ions, viz. alkali (Na⁺, K⁺), alkaline earth (Mg²⁺, Ca²⁺), and transition-metal ions ((Mn²⁺, Fe³⁺, Co³⁺, Ni²⁺, Cu²⁺, Zn²⁺) and Pb²⁺, Ag⁺ did not interfere. The lowest detection limit for Cr³⁺ was calculated to be 3.6 × 10⁻⁷ mol L⁻¹ within a very short responsive time (15–20 s) in ethanol–water (1 : 5, v/v) HEPES buffer (0.1 M, pH 7.4) at 27 °C. The sensor is efficient for detection of Cr³⁺ in vitro, developing a good image of the biological organelles.