The Fluorescent Brightener 121, with the CAS registry number 2744-49-2 and EINECS registry number 220-378-2, has the systematic name of 4-[3-(4-chlorophenyl)-4,5-dihydro-1H-pyrazol-1-yl]benzenesulfonamide. And the molecular formula of the chemical is C₁₅H₁₄ClN₃O₂S.

The characteristics of Fluorescent Brightener 121 are as followings: (1)ACD/LogP: 0.78; (2)# of Rule of 5 Violations: 0; (3)ACD/LogD (pH 5.5): 0.78; (4)ACD/LogD (pH 7.4): 0.78; (5)ACD/BCF (pH 5.5): 2.31; (6)ACD/BCF (pH 7.4): 2.3; (7)ACD/KOC (pH 5.5): 63.3; (8)ACD/KOC (pH 7.4): 63.24; (9)#H bond acceptors: 5; (10)#H bond donors: 2; (11)#Freely Rotating Bonds: 3; (12)Polar Surface Area: 61.36 Å²; (13)Index of Refraction: 1.682; (14)Molar Refractivity: 87.3 cm³; (15)Molar Volume: 230.4 cm³; (16)Polarizability: 34.61×10^-24cm³; (17)Surface Tension: 59.5 dyne/cm; (18)Density: 1.45 g/cm³; (19)Flash Point: 277.5 °C; (20)Enthalpy of Vaporization: 81.16 kJ/mol; (21)Boiling Point: 535.2 °C at 760 mmHg; (22)Vapour Pressure: 1.57E-11 mmHg at 25°C. 

Addtionally, the following datas could be converted into the molecular structure:
(1)SMILES: O=S(=O)(c1ccc(cc1)N3/N=C(/c2ccc(Cl)cc2)CC3)N
(2)InChI: InChI=1/C15H14ClN3O2S/c16-12-3-1-11(2-4-12)15-9-10-19(18-15)13-5-7-14(8-6-13)22(17,20)21/h1-8H,9-10H2,(H2,17,20,21)
(3)InChIKey: VZTHUHAJEZPWNC-UHFFFAOYAW