Polarized Fluorescence of N-Salicylideneaniline Derivatives Formed by In Situ Exchange from N-Benzylideneaniline Side Groups in Photoaligned Liquid Crystalline Copolymer Films

Abstract

Polarized fluorescence of oriented N-salicylideneaniline (SA) derivatives is explored based on the thermally stimulated photoinduced molecular reorientation of liquid crystalline (LC) copolymethacrylate with N-benzylideneaniline derivative (NBA2) and benzoic acid (BA) side groups. The LC copolymer films show significant cooperative molecular reorientation of the NBA2 and BA side groups (D > 0.7). Subsequent thermal hydrolysis of the NBA2 side groups yields free phenylamine moieties. These moieties can form oriented SA derivatives via in situ condensation with 2-hydroxybenzaldehyde derivatives. The excited-state intermolecular proton transfer of the oriented SA molecules induces polarized fluorescence at 510–548 nm with a polarization ratio up to 6.2. Direct in situ exchange from the oriented NBA2 to SA derivatives achieves polarized fluorescence similar to that of the SA side groups.

Photoinduced Reorientation and Polarized Fluorescence of a Photoalignable Liquid Crystalline Polymer

“…By contrast, the D value decreases when the exposure energy exceeds 3 gardless of the annealing temperature (Figures 3c and S3c,d). As the photoreac Annealing the exposed P4 films generates a significant in-plane thermal stimulation of the orientation similar to the cases of P1-P3 films [26][27][28][29][30]. Figure 3a shows the change in the polarized absorption spectra of a P4 film after exposure to linearly polarized 313 nm light for 5 J/cm 2 and subsequent annealing at 120 • C for 10 min.…”

“…The photoinduced in-plane reorientation initially occurs, but the simultaneous photo-Fries rearrangement of the phenyl benzoate moieties at a high exposure dose restricts the in-plane motion of the mesogenic side groups (Scheme 1). Annealing the exposed P4 films generates a significant in-plane thermal stimulation of the orientation similar to the cases of P1-P3 films [26][27][28][29][30]. Figure 3a shows the change in the polarized absorption spectra of a P4 film after exposure to linearly polarized 313 nm light for 5 J/cm 2 and subsequent annealing at 120 °C for 10 min.…”

“…Copolymers with a methacrylate composed of benzoic acid side groups show thermally stimulated cooperative molecular reorientation [28,29]. The NBA side groups in these reoriented films can be hydrolyzed at elevated temperatures under humid conditions, yielding oriented films with free benzaldehyde (from NBA1) or phenylamine (from NBA2) side moieties [28,29]. In situ condensation with phenylamine or 2-hydroxybenzaldehyde derivatives reforms different types of NBA or N-salicylideneaniline derivatives, generating reoriented films with high functionalities, such as high birefringence, thermal stability, and polarized fluorescence [28,29].…”

“…The NBA side groups in these reoriented films can be hydrolyzed at elevated temperatures under humid conditions, yielding oriented films with free benzaldehyde (from NBA1) or phenylamine (from NBA2) side moieties [28,29]. In situ condensation with phenylamine or 2-hydroxybenzaldehyde derivatives reforms different types of NBA or N-salicylideneaniline derivatives, generating reoriented films with high functionalities, such as high birefringence, thermal stability, and polarized fluorescence [28,29]. However, the hydrolyzed-oriented films should exhibit the LC characteristics to maintain the oriented structure upon thermal hydrolysis.…”

“…2022, 12, 6440 2 molecular reorientation using linearly polarized 313 and 365 nm light [26,27]. Copolym with a methacrylate composed of benzoic acid side groups show thermally stimul cooperative molecular reorientation [28,29]. The NBA side groups in these reorie films can be hydrolyzed at elevated temperatures under humid conditions, yielding ented films with free benzaldehyde (from NBA1) or phenylamine (from NBA2) side m eties [28,29].…”