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]benzoth iazole methiodide (BTM), 2-[4-bis(hexadecyl)aminostyryl]benzoxazole methiod ide (BOM), and 2-[4-bis(hexadecyl)aminostyryl]benzimidazole methiodide (BIM ), were synthesized and successfully transferred onto the conducting transp arent indium-tin oxide (ITO) electrode as H-aggregates by using a Langmuir- Blodgett (LB) technique. The photoelectrochemistry of the dye monolayers wa s investigated in a traditional three-electrode cell. The coincidence of th eir action spectra with the absorption spectra on the ITO electrodes indica ted that the aggregates of the dyes on the ITO electrodes were responsible for the generation of the cathodic photocurrents. Some factors such as appl ied bias voltage, electron donors and acceptors on the photocurrent generat ion 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 respec tively. Semiempirical calculations indicated that charge-separated states o f the dyes upon illumination are a key requirement for the photocurrent gen eration. A common mechanism of photocurrent generation in this system was p roposed based on the experiments. Experimental results indicated that heter oatoms in the acceptor parts of the dyes have a great effect on the photocu rrent generation.