Herein, we have presented a simple organic compound, benzo [a]fluorenone, as a highly fluorescent chemosensor for the detection of 2,4,6-trinitrotoluene (TNT) in solution phase with a limit of detection (LOD) down to 4 nM. This probe is more sensitive towards TNT than 2,4-dinitrotoluene (DNT) and picric acid (PA). The photophysical studies revealed that it is static quenching through a ground state interaction between TNT and the title compound.Explosives are a matter of great concern these days for the security of humans around the globe. Among the common explosives, nitroaromatics are capable of releasing tremendous amount of heat and energy by self-oxidation and thus make them as choice for destruction purposes. [1,2] Also, TNT is one of the well-known nitroaromatic explosive which causes hazardous environmental pollutions. [3,4] Sensing explosives efficiently saves the lives of people from the terror activities of miscreants. To sense TNT, different analytical methods based on electrochemistry, [5][6][7] gas and liquid chromatography, [5] mass spectrometry, [5] metal detection, [5] surface-enhanced Raman spectroscopy (SERS), [5] X-ray diffraction and nuclear quadrupole resonance (NQR) [5,8] etc. have been efficiently employed. However, the realistic application of these methods is being restricted due to several drawbacks such as requirement of expensive equipment, lack of selectivity, complicated procedures such as sophisticated vapor sampling, instrument calibration. In this sense, fluorescence quenching technique has been proven as the most convenient and straightforward method to sense TNT due to its inherent sensitivity, high selectivity, fast responses, easy sampling and portability etc. Consequently, fluorescent sensors such as molecularly imprinted polymers (MIPs), [9] conjugated organic/inorganic polymers, [10][11][12] covalent organic polymers (COPs), [13] porous metal-organic frameworks (MOFs), [14] organic-inorganic hybrid materials, [15,16] luminescent gels, [17] discrete macrocycles/ cages, [18,19] dendrimers, [20] nano materials, [21,22] etc. have been utilized for TNT detection. Although the reported methods involving fluorescence quenching are having good selectivity and low detection limit, limitation associated with the synthesis of the sensor materials such as efficiency and scalability makes them less attractive. Thus, development of simple organic molecule based fluorescent sensors to sense TNT has drawn attention due to their easy synthesis, easy purification, better reproducibility and scalability. Moreover, their photophysical properties can effectively be tuned using steric and electronic effects. Furthermore, unlike polymers and many metal-organic frameworks (MOFs) based sensors, small molecule based sensors are soluble in most of the common solvents, which gives additional advantages for practical applications. Only a very few reports are available on simple organic molecule based chemosensor for the trace detection of TNT. [23][24][25][26] For instance, Patil and co-workers report...