Substituent effects on intramolecular charge-transfer behaviour of styrylheterocycles

To understand the influence of substituents on intramolecular charge transfer (ICT), absorption and emission spectra were measured for several derivatives of 2-styrylquinoline (2-StQ), 2-styrylpyridine (2-StP) and 2-styrylthiophene (2-StT) systems. A strong donor, such as an N,N-dimethylamino group can produce an ICT compound in these systems, and the excited state dipole moments were measured using a solvatochromic method. Quinoline and pyridine can only act as accepters. Depending on substituents, the thiophene ring could be a donor or an acceptor. For same donor in our systems, the strength order of different accepters is quinoline>naphthalene>pyridine>thiophene Besides electronic effect, steric conformation is also an important factor in ICT molecules. Protonation and hydrogen bonding at acceptor site show red-shift in absorption maxima. The degree of shift depends on the substituents. Interaction at a donor site gives the opposite result. There is a linear relation between excited state dipole moments and absorption energy. (C) 2000 Elsevier Science S.A. All rights reserved.