Synthesis and optical properties of 2-functionally substituted 4,5-dihydrothieno[3,2-c]quinolines

N-Protected 4-(anilinomethyl)thiophene-2-carbaldehydes were prepared by the reaction of easily available 4-chloromethylthiophene-2-carbaldehyde with N-(2-halogenophenyl) substituted acetamides, 4-methylbenzenesulfonamides and carbamates in the presence of K₂CO₃ or Cs₂CO₃. The compounds obtained were converted to 4,5-dihydrothieno [3,2-c]quinoline-2-carbaldehydes by palladium catalyzed intramolecular cyclization in homogenous or heterogenous (Pd/C) conditions with good yields and subsequently used for preparing of 2-functionally substituted thieno [3,2-c]quinoline derivatives (nitriles, carboxamides, carboxylic acids, esters). The optical properties of 2-functionally substituted thieno[3,2-c]quinolines and 4H-thieno[3,2-c]chromenes have been studied. Moderate to high fluorescence quantum yields are observed for these compounds ranging from 0.15 to 0.87. Structure - optical properties relationships have been established for the compounds synthesized, and their prospective application as invisible ink dyes was practically demonstrated.