Synthesis and photoisomerization of poly(1‐methylpropargyl ester)s carrying azobenzene moieties

Abstract

Optically active 1-methylpropargyl esters bearing azobenzene groups, namely, (S)-(À)-3-methyl-3-{4-[4-(n-butyloxy)phenylazophenyl]carbonyl}oxy-1-propyne (1), (S)-(À)-3-methyl-3-{4-[4-(n-hexyloxy)phenylazophenyl]carbonyl}oxy-1-propyne (2), and (S)-(À)-3-methyl-3-{4-[4-(n-octyloxy)phenylazophenyl]carbonyl}oxy-1-propyne (3) were synthesized and polymerized with Rh þ (nbd)[g 6 -C 6 H 5 B À (C 6 H 5 ) 3 ] (nbd, norbornadiene) as a catalyst to afford the corresponding poly(1-methyloropargyl ester)s with moderate molecular weights (M n ¼ 24,000-31,300) in good yields (79-84%). Polymers were soluble in common organic solvents including toluene, CHCl 3 , CH 2 Cl 2 , THF, and DMSO, whereas insoluble in diethyl ether, n-hexane, and methanol. Large optical rotations and strong CD signals demonstrated that all the polymers take a helical structure with a predominantly one-handed screw sense. The helical structure of the polymers changed with the addition of MeOH and heat. The trans-azobenzene of the polymer side chains isomerized into cis on UV irradiation, which was accompanied with drastic helical conformational changes of the polymer backbone. The cis-azobenzene moiety reisomerized into trans on visible-light irradiation, which induced the recovery of chiral geometry of azobenzene moieties in the side chain. Conformational analysis revealed that the polymers form a tightly twisted right-handed helical structure with a dihedral angle of 70 at the single bond of the main chain.

Behaviors of self‐assembled diblock copolymer with pendant photosensitive azobenzene segments

“…The results are consistent with the AFM images shown in Figure 4. In case of high copolymer concentration film shown in Figure 4(c), the interaction from the silicon substrate on self‐assembly of hydrophilic and hydrophobic segments may extremely decrease because of the increase of film thickness 26…”

“…Recent studies show that polymers containing azobenzenes (azo polymers for short) can exhibit fascinating photoresponsive variations, such as phase transition,25, 26 chromophore orientation,27 surface‐relief‐grating formation,28 and photomechanical bending 29. The variations are triggered by the trans – cis photoisomerization of the azobenzenes.…”

Helical poly(phenylacetylene)s containing schiff-base and amino groups: Synthesis, secondary structures, and responsiveness to benzoic acid

“…Since the pioneering work by Ciardelli on helical poly(1‐alkyne)s, a variety of helical polyacetylene derivatives based on optically active side groups have been successfully synthesized; for example, poly(alkyl propiolate)s, poly( N ‐propargylalkylamide)s, poly( N ‐propargylcarbamate)s, and poly(methylpropargyl ester)s . As examples of dynamic helical polymers, some polyacetylenes undergo helix/random coil transition and/or helix inversion by external stimuli such as temperature, light, and change of medium conditions including polarity and pH . These properties are attractive in a wide variety of fields including life science, pharmacy, and chemical engineering.…”

Modulating structural stability and acid sensitivity of photosensitive polymer micelles simply via one‐batch UV irradiation

“…There has been growing interest in developing polymer micelles whose aggregations and functions can be controlled by light since the first report on photocontrollable polymer micelles in 2004 1–4. Much effort was dedicated to the association and disruption of polymer micelles or vesicles via photoisomerization to change the polarity or shifting the hydrophilic‐hydrophobic balance 5–16. Another chemistry extensively employed was the cleavage of photolabile groups 17–23.…”