PHOTOLITHOGRAPHY OF SELF-ASSEMBLED MONOLAYERS - OPTIMIZATION OF PROTECTING GROUPS BY AN ELECTROANALYTICAL METHOD

Patterned surfaces presenting a high density of chemically reactive fu nctional groups can be prepared through photolithography of self-assem bled monolayers (SAM). In this paper, we report the synthesis and the evaluation of three reagents that can be used in SAM-photolithographic applications. These reagents are made up of a triethoxysilylpropylami ne moiety in which the amine is temporarily blocked by photolabile pro tecting groups: NVOC (o-nitroveratryloxycarbonyl), ONE (o-nitrobenzyl) , or DDZ ha,alpha-dimethyl-3,5-dimethoxybenzyloxycarbonyl). The presen ce of the triethoxysilyl group allows self-assembled monolayer formati on. Release of chemically reactive amino groups is achieved by irradia tion of the surface. An electroanalytical method was developed and use d to monitor and optimize the three steps of the methodology occurring on surfaces: monolayer formation, photodeprotection, and subsequent f unctionalization of the released amino groups. Quantitative informatio n on the efficiency of the photodeprotection step was obtained by this method. It was found that the DDZ group is superior to the ONB and NV OC photolabile protecting groups for SAM-photolithographic application s. Percentages of liberated amino groups are generally above 50% with the DDZ group, while they are generally inferior to 25% and 2% for NVO C and ONE, respectively. These differences are attributed to the destr uction of some of the released amino groups through a subsequent react ion with the photoproduct, o-nitrosobenzaldehyde for ONE and 3,4-dimet hoxy-6-nitrosobenzaldehyde for NVOC, and to partial loss or destructio n of the monolayer during prolonged irradiations.