## 3 Results and Discussion
### In Situ Formation of Oriented \(N\)-Salicylideneananiline Derivatives  
The formation of oriented \(N\)-salicylideneananiline derivatives is carried out by coating HBA, FHA, or CNA in an ethylene glycol solution (1.0 wt/vol%) onto a hydrolyzed **P4** film and subsequently annealing at 100 \({}^{\circ}\)C for 10 min. Figure 6 shows the changes in the polarized absorption spectrum of reoriented-hydrolyzed **P4** films [DH = (a) 60% and (b) 94%] before and after the formation of the \(N\)-salicylideneaniline derivatives using HBA and their polarized fluorescence spectra. For both films, a new absorption band at 340 nm is observed, but its intensity differs. The DH = 94% film displays a larger absorbance at 340 nm due to the higher amount of \(N\)-salicylideneaniline derivative formation. It should be mentioned that both films show a similar \(D\) at 340 nm (\(D_{340}\) = 0.72-0.76), but the initial \(D_{260}\) value of the hydrolyzed film is lower for the higher DH film. This indicates that the thermal condensation process simultaneously induces thermally stimulated molecular reorientation of the formed \(N\)-salicylideneaniline moieties. Additionally, the use of FHA and CNA for the condensation shows similar results, where the \(D_{340}\) values after condensation are 0.64 (FHA) and 0.65 (CNA) when using DH = 90% films (Figure 6c,d).  
Figure 4: Changes in the polarized absorption spectrum of oriented **P4** films before and after hydrolysis. Initial oriented films are prepared by exposing to linearly polarized 313 nm light for 3/cm\({}^{2}\) and subsequent annealing at 180 \({}^{\circ}\)C for 10 min. Hydrolysis is carried out by immersing acetic acid/water (**a**) 1/5 and (**b**) 1/3 solution at 50 \({}^{\circ}\)C for 10 min and subsequent rinsing with methanol and diethyl ether. (**c**) Changes in the polarized FTIR spectra of an oriented **P4** film before and after hydrolysis. Hydrolysis is carried out by immersing acetic acid/water 1/3 solution at 50 \({}^{\circ}\)C for 10 min.  
Figure 5: Change in the transmittance of a hydrolyzed oriented **P4** film upon heating between crossed polarizers.  
Polarized fluorescence is useful for polarized light-emitting or polarization-sensing devices [34; 35]. Several studies have studied the polarized fluorescence of LC materials based on the photoalignment technique [34; 35; 36; 37]. The \(N\)-salicylideneaniline derivative-formed films exhibit fluorescent emission with a large Stokes shift due to excited-state intermolecular proton transfer (ESIPT) (Figure 6a-d and insets) [38; 39]. For HBA-introduced films, \(\lambda_{\text{max}}\) of the fluorescence is 530 nm, and a higher emission is observed when using a higher DH film (\(P\) = 2.3-2.4) because more oriented mesogens with \(N\)-salicylideneaniline moieties are formed. Similar polarized fluorescent behaviors are observed for the FHA- and CNA-introduced films (\(\lambda_{\text{max}}\) = 547 nm, \(P\) = 2.8 for FHA, \(\lambda_{\text{max}}\) = 540 nm, \(P\) = 3.4 for CNA). These fluorescent behaviors of oriented \(N\)-salicylideneaniline derivatives are similar to those obtained by in situ condensation using oriented copolymer films of NBA2 and benzoic acid side groups [28]. However, the fluorescent intensity is larger due to the higher content of \(N\)-salicylideneaniline derivative-containing mesogenic side groups.