Key Laboratory of Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004, China

Self-organized dithieno [3,2-b:2’,3’-d] thiophene-2,5-dicarboxylic acid (A) and dithieno [2,3-b:3’,2’-d] thiophene-2,5- dicarboxylic acid (B) films were prepared through solvent-induced order-disorder transition method. The arrangement of the two molecules on substrates were observed by atomic force microscopy (AFM), which demonstrated that A was arranged orderly in a certain angle on mica, while B was flat-flying on mica. The optical and conductance properties in micro region of these two com-pound films were characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy and conductive atomic force mi-croscopy (C-AFM). The results revealed that the fluorescence and absorption peaks of A had a large red shift in comparison with those of B. The conductance of the J-aggregates for A is three orders magnitude higher than that of B. It is concluded that the large conductance difference mainly comes from different aggregation structures and orientations of these two molecules on substrate.

This work was supported by the National Natural Science Foundation of China (Grant Nos. 20672028, 10874040, 20803018), Program for New Century Excellent Talent in University (Grant Nos. NCET-04-0653, NCET-05-0610) and Cultivation Fund of Key Scientific and Technical Innovation Project, Ministry of Education of China (Grant No. 708062).