Monolayers excited states within

Condensed monolayer films of pure 6 polymerized rapidly, as did mixed 6/DSPE films of up to 75% DSPE, provided the monolayers were in the condensed state [33], In the liquid-expanded state, polymerization did not occur. In the condensed state, lateral diffusion of individual lipids within the monolayer is severely restricted compared to the liquid-like state. This precludes initiation of polymerization by diffusive encounter between excited-state and ground-state diacetylene lipids. In order for polymerization to occur in the condensed state, the film must be separated into domains consisting of either pure 6 or pure DSPE. A demonstration that the rates of photopolymerization for pure 6 and mixed 6/DSPE monolayers are equal would be a more stringent test for separate domains of the lipids, but no kinetic data have been reported for this system. 

The Norrish type 11 reaction of an aryl ketone monolayer-protected coUoid was investigated by Worken-tin and co-workers.Photolysis of a mercaptoalkanophenone-modified gold colloid generates free acetophenone in solution and the modified monolayer-protected clusters via the triplet excited state and the 1,4-biradical intermediate. The reaction has been developed as a probe of conformational mobihty within the monolayer environment. 

A close-packed monolayer of long, planar molecules must necessarily contain at least "islands" of local order in which molecules are packed plane-to-plane. One notices that crystals of these dyes tend to pack in sheets, within which the molecules have their long axes parallel to one another and parallel to the plane of the sheet. The molecular short axes are nearly perpendicular to the plane of the sheet, and the intermolecular contacts within the sheet tend to occur at the graphitic distance, except for molecules which are bent or twisted out of planarity. Twisted molecules ("overcrowded" in Brooker s classification) generally make poor sensitizers, probably because they have a fast route of deexcitation directly from the excited singlet state to the ground state opened by the existence of the twisted, stressed structure. 

---