Hiroshi Ohnuma

Absorption and Fluorescence Spectra of Polydiacetylenes (4BCMU and 3BCMU) in Solution

Absorption and fluorescence spectra have been measured on soluble poly-diacetylenes (4BCMU, 3BCMU), having the side group R=n-BCMU (n-butoxy carbonyl methyl urethane, n=4, 3), in chloroform/n-hexane mixture solvents for various solvent compositions and temperatures. The observed features of the absorption spectra are interpreted by assuming that two types of the coil-to-rod conformational transition take place in the two distinct isomeric bond-structures, which presumably correspond to the acetylenic and butatrienic types, respectively. Experimental phase-diagrams are presented as functions of solvent composition and temperature. Fluorescence bands were observed in rod-like polymer solutions at low temperatures. It is suggested that these largely Stokes-shifted emission bands are due to the self-trapped π-π * excitons on the one-dimensional polymer chains.

Fluorescence spectrum and lifetime of urethane-substituted polydiacetylene in solution

Abstract The spectrum and lifetime of the fluorescence from water soluble poly[4,6-decadiyn-1,10-diol-bis(carboxyl-methyl-urethane)] at three pH values (7.5, 7.1, and 6.2) were measured at room temperature. At these pH values the lifetime was 9 ± 3 ps and the spectrum was independent of the excitation wavelength. Discussion was made on the basis of Forster-type energy transfer among the conjugated sequences of repeat units.

Structure and disorder of polydiacetylene: poly(4BCMU)

Abstract Poly[dodecadiyn-1,12-diol-bis(n-butoxycarbonyl-methyl-urethane)][poly(4BCMU)] can exist in four crystal forms, I, II, III and the high-temperature form in the crystalline state and the melt-cooled (cast) form in the unoriented state. Among these, forms I and II give similar diffraction patterns: the equators give the discrete spots while the layer lines give the diffuse streaks parallel to the B ∗ -axes. Both forms have the almost same fiber identity period (4.87 A for form I and 4.89 A for form II) which show the extended planar zigzag main-chain conformation. The equatorial reflections of forms I and II can be indexed by the rectangular subcell with parameters, a′ = 5.35 A, b′ = 54.5 A and the plane group, pgg, except for few weak superlattice spots, and, by the cell with a′ = 5.35 A, b = 54.5 A and the plane group, pgg, respectively. Both forms assume the very similar structures on the c-projection. The diffuse streaks on the layer lines suggest that the regular sheet structures are formed parallel to the ac-planes and the sheet structures are disordered with respect to the heights and stacked in the b-direction. The structural difference between forms I and II arises from the difference in sheet structure: the repeating unit in the sheet structure of form I is of one molecular chain while that of form II is of seven chains.