Impact of the Air Atmosphere on Photoinduced Chain Polymerization in Self-Assembled Monolayers of Diacetylene on Graphite

We have studied the effect of the reaction environment on the photoinduced chain polymerization in self-assembled monolayers of a diacetylene compound 10,12-pentacosadiyn-1-ol on graphite, using scanning tunneling microscopy. Comparing the polymerization behaviors in air and in vacuum, we show that the polymer generation efficiency is considerably enhanced under vacuum because of suppressed collisional quenching of the photoexcited radicals by oxygen molecules. We also find that the polymer chain length tends to increase in vacuum as a result of the inhibition of deactivation of reactive species for the polymer chain growth due to oxidation.