A First Study of Langmuir-Blodgett Films of 1-[N-(n-Hexadecyl)-4-pyridinio]-2-[5-(dicyanomethanidyl) thien-2-yl]ethene

The dye 1-[N-(n-hexadecyl)-4-pyridinio)-2-[5-(dicyanomethanidyl) thien-2-yl]ethene (C₁₆H₃₃-PDCNTE), 1, is a new zwitterionic compound belonging to a new class of negatively solvatochromicpush-pull molecules containing a negatively charged dicyanomethanide as donor group and a positively charged N-alkylpyridinium as acceptor group linked via an extended Ï€-electron bridge.¹ In a previous work, we have shown the interesting properties of 4-[5-(dicyanomethanidyl)thien-2-yl]-N-(n-hexadecyl)pyridinium (C₁₆H₃₃-PDCNT),² another negatively solvatochromic betaine dye (differing from C₁₆H₃₃-PDCNTE with the absence of the ethene bridge between the pyridinium and thiophene moieties) which belongs to this class of functional dyes, which seems to be very promising for second-order nonlinear optical effects that can be accomplished for example by noncentrosymmetric Langmuir-Blodgett (LB) films.3-5 LB films of C₁₆H₃₃-PDCNT prepared according to a proper procedure show a sharp photobleachable UV-vis absorption band that has interesting applications in a field of great interest such as the optical data storage.3-14 In this work, we show that also LBfilms of C₁₆H₃₃-PDCNTE can be prepared in order to show a sharp photobleachableUV-vis absorption band. An LB film containing one monolayer of C₁₆H₃₃-PDCNT and one monolayer of C₁₆H₃₃-PDCNTE was shown to allow for efficient multifrequency optical data storage because the two sharp UV-vis absorption bands of the two substances could be selectively photobleached even with a peak-to-peak separation of less than 50 nm.¹⁵