A new crystal structure and fluorescence property of N-2-flurobenzoyl-N′-4-tolylthiourea

A new crystal of N-2-flurobenzoyl-N′-4-tolylthiourea (FBTT) was obtained from slow evaporation of solvent benzene and the crystal structure of FBTT was determined by X-ray diffraction method. The packing mode of FBTT molecules was affected by crystallization conditions. The new crystal of FBTT crystallizes in the monoclinic with the space group C2/c, and it was stabilized by two pairs of intermolecular interactions. The first pair of intermolecular hydrogen bonds are N(1#)–H(1#)⋯S(1) and N(1)–H(1)⋯S(1#1), the second pair of intermolecular hydrogen bonds, are C(11#)–H(11#)⋯O(1) and C(11)–H(11)⋯O(1#). There also have other unpaired intermolecular hydrogen bonds C(15)–H(15C)⋯O(1#1) and C(15#2)–H(15#2)⋯O(1). Double fluorescence bands are observed in both non-polar and polar solvents. The fluorescence emission at 350–360 nm originates from the transitions of π∗ → π state and is assigned to S2 fluorescence for the nature of LE state. The long wavelength fluorescence emission with large Stokes shift is the characteristic of ESIPT state. All experimental results are supported by MP2 and CASSCF calculations.

► A new crystal structure of thiourea is determined by X-ray diffraction method. ► The crystal is stabilized by some intra- and intermolecular hydrogen bonding interactions. ► The fluorescence bands with large Stokes shift present an ESIPT fluorescence characteristic. ► The fluorescence emission at 350–360nm is assigned to S2 fluorescence for the nature of LE state. ► The experimental results are supported by MP2 and CASSCF quantum chemical calculations.