## 3 Results and Discussion
### Photophysical Properties  
Table 1 and Figure 2 provide a comprehensive summary of the UV-Vis absorption and photoluminescence (PL) spectra of the synthesized compounds in both solution and film states. In the solution state, TP-AFF-TP and TP-ASF exhibit UV maximum values of 410 and 419 nm and PL maximum values of 426, 447 nm and 439, 456 nm, respectively. The solution FWHM values were at 55 and 57 nm, respectively. TP-ASF has UV and PL maximum value in the red-shifted region more than that of TP-AFF-TP. Also, TP-ASF had a slightly broader FWHM compared to TP-AFF-TP. Through density functional theory (DFT), it is confirmed that most electron density exists on anthracene in HOMO and LUMO energy levels for TP-AFF-TP and TP-ASF. In the case of TP-ASF, the substitution of the side group on the anthracene moiety, which possesses a higher electron density, might have led to lengthen the intramolecular conjugation and the generation of numerous electron transition states, potentially contributing to a large Stoke-shift result (see Figure 3). In the film state, the UV maximum values of TP-AFF-TP and TP-ASF show 416 nm and 425 nm, respectively. There was a difference of 6 nm for both the solution and film state. Moreover, the photoluminescence (PL) spectra of TP-AFF-TP and TP-ASE, when in a film state, displayed red shifts of 30 nm and 11 nm, respectively, in contrast to their respective spectra in the solution state. The commonly observed phenomenon involves the red shifts in UV and PL peak wavelengths, along with broader full width at half maximum (FWHM) values, during the transition from a solution to a film state. This is attributed to the intermolecular interactions that arise from the reduced intermolecular distances in the film state. However, in contrast to the solution, TP-AFF-TP exhibited luminescence in the longer wavelength region compared to TP-ASF. In addition, FWHM values of TP-AFF-TP and TP-ASF exhibit 96 nm and 68 nm in the film state, respectively. This means that TP-AFF-TP has stronger intermolecular interaction than that of TP-ASF. This is because TP-ASF has its side group, TP, substituted on the anthracene moiety, which can suppress the planar  
packing of anthracene. However, TP-AFF-TP has its side group already substituted on the highly twisted fluorene portion, and this might have been ineffective in preventing effective intermolecular \(\pi\)-\(\pi\) stacking. Therefore, incorporating a large side group at a strategically selected location on the central molecule can efficiently impede \(\pi\)-\(\pi\) stacking interactions. This approach effectively mitigates the possibility of emission suppression. Additionally, such alterations have the capacity to influence the quantum efficiency of photoluminescence (PLQE). As a result of PLQE measurement, PLQE values of TP-AFF-TP and TP-ASF were 45 and 88% in the solution state, and 20 and 53% in the film state. The values of the transition contribution and the oscillator strength through the time-dependent DFT (TD-DFT) calculation between HOMO and LUMO levels showed 83.8% and 0.117 in TP-AFF-TP and 91.7% and 0.262 in TP-ASF, respectively, as shown in Table S1. This causes TP-ASF with higher oscillator strength value to exhibit higher PLQE. In order to measure the highest occupied molecular orbital (HOMO) values of the synthesized materials, ultraviolet photon spectroscopy (UPS) of AC-II and optical absorption spectroscopy were carried out. As indicated in Table 1, the highest occupied molecular orbital (HOMO) levels were measured at 5.80 eV and 5.72 eV, while the lowest unoccupied molecular orbital (LUMO) levels were recorded at 2.79 eV and 2.80 eV for TP-AFF-TP and TP-ASF, respectively, within the blue region. The band gaps of TP-AFF-TP and TP-ASF were 3.01 eV and 2.92 eV, respectively. Decomposition temperature (T\({}_{\rm d}\)) by TGA, which means thermal stability of the synthesized materials was measured. The T\({}_{\rm d}\) values for TP-AFF-TP and TP-ASF were 481 and 407 \({}^{\circ}\)C, respectively.