Effect of heteroatoms on photocurrent generation from a series of styryl dye Langmuir-Blodgett films

A series of amphiphilic styryl dyes, 2-[4- bis(hexadecyl)aminostyryl]benzothiazole methiodide (BTM), 2-[4- bis(hexadecyl)aminostyryl]benzoxazole methiodide (BOM), and 2-[4- bis(hexadecyl)aminostyryl]benzimidazole methiodide (BIM), were synthesized and successfully transferred onto the conducting transparent indium-tin oxide (ITO) electrode as H-aggregates by using a Langmuir-Blodgett (LB) technique. The photoelectrochemistry of the dye monolayers was investigated in a traditional three-electrode cell. The coincidence of their action spectra with the absorption spectra on the ITO electrodes indicated that the aggregates of the dyes on the ITO electrodes were responsible for the generation of the cathodic photocurrents. Some factors such as applied bias voltage, electron donors and acceptors on the photocurrent generation have also been investigated. Under favorable conditions (-200 mV, 1 mg ml^-1 methylviologen diiodide (MV²⁺)), the photoelectric conversion quantum yield can reach 4.2%, 0.96%, and 1.19% for BTM, BOM and BIM respectively. Semiempirical calculations indicated that charge-separated states of the dyes upon illumination are a key requirement for the photocurrent generation. A common mechanism of photocurrent generation in this system was proposed based on the experiments. Experimental results indicated that heteroatoms in the acceptor parts of the dyes have a great effect on the photocurrent generation.