Orientation and Microenvironment of Naphthalene Guest in the Host Nanoporous Phase of Syndiotactic Polystyrene

Abstract

Syndiotactic polystyrene (s-PS) films including a fluorescent guest (naphthalene, NP) in their nanoporous δ crystalline phase have been prepared and characterized by X-ray diffraction, infrared linear dichroism, molecular modeling, and fluorescence depolarization techniques. A nearly perpendicular orientation of the fused rings of NP guest molecules with respect to the chain axis of the δ crystalline structure has been established by molecular mechanics and by evaluation of directions of transition moment vectors of infrared vibrational modes. The fluorescence depolarization is more efficient for NP guest molecules into the host phase than for NP molecules simply absorbed in the amorphous phase. This could be due to a more efficient resonance energy transfer between guest molecules, possibly associated with their ordered positioning and orientation into the host nanoporous polymeric crystallites.

Understanding at molecular level of nanoporous and co-crystalline materials based on syndiotactic polystyrene

“…When the degree of occupancy of the crystalline cavities is low, due to the related crystalline disorder, the X-ray diffraction method is not able to give reliable information relative to the guest location and orientation. However, infrared linear dichroism measurements on uniaxially oriented films easily allow establishing the orientation of the guest molecules with respect to the host chain axis [57,62,64].…”

“…On this basis, films presenting s-PS/active guest co-crystals have been proposed as advanced materials, mainly for optical applications (e.g. fluorescent, photo-reactive, chromophore and nonlinear optical materials) [57][58][59][60][61][62][63].…”

Polymorphism of syndiotactic polystyrene: γ phase crystallization induced by bulky non-guest solvents

“…Moreover, several molecular complexes between different guest molecules and s-PS s(2/1)2 helical chains (clathrate [3][4][5][6][7] and intercalate [8] crystalline phases) have been also obtained. The polymorphic behavior of s-PS is further complicated by the occurrence of different modifications of the trans planar a-and b-phases, ranging between limit disordered (a 0 and b 0 ) and limit ordered (a 00 and b 00 ) modifications [1,2,[8][9][10][11][12][13][14].…”

Polymer co-crystalline films for photonics

“…naphthalene [25]) can form clathrate co-crystals with sPS while other fluorescent molecules (e.g. 1,4-dimethyl-naphthalene [14]) form intercalate co-crystals.…”