A Simple One‐Pot Synthesis of Solvatofluorescent Push‐Pull Thiophenes

Depending on the substitution patterns in the sulfanes 1 , two different types of thiophenes 3 and 4 can be obtained upon cyclization with a bis ‐ imidoyl chloride 2 . Whereas thiodiglycolic acid diester yielded a thiophene derivative with the expected symmetrical structure, thiodiacetonitrile gives a derivative with an asymmetrical substitution pattern (2,3‐arylamino/4,5‐dicyano). This unexpected finding was confirmed by single‐crystal X‐ray analysis and possibly originates from a 1,2‐rearrangement of a thietanium salt intermediate. These new push‐pull thiophenes are easily accessible in a single step from simple starting materials. Unlike in the case of the derivatives 3 , the substitution pattern in 4 was not previously known. A simple hydrolysis of compounds 4 offers a new and efficient route to derivatives of thiomaleic acid anhydrides 6 . The 2,3‐dicyano‐4,5‐bis(arylamino)thiophenes 4 exhibit strong solvatofluorescence with unusually large Stokes shifts. Quantum chemical calculations explain the large Stokes shifts as most probably being due to strong structural relaxation upon excitation to the S 1 state.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)