1：Experimental Design and Method Selection:

A two-step synthetic protocol was used, starting from 4-fluoro-2-methylpyrimidine N-oxides. The first step involved SNAr reactions to introduce amino groups, and the second step involved Knoevenagel condensation with various aldehydes under basic conditions (50% or 10% aqueous NaOH with TEBAC catalyst) to form π-conjugated systems.

2：Sample Selection and Data Sources:

A series of 17 novel pyrimidine N-oxide derivatives (3a-r) were synthesized and characterized. Starting materials were commercially available or synthesized via described methods.

3：List of Experimental Equipment and Materials:

Equipment included a 400 MHz NMR spectrometer (Agilent 400-MR), UV-vis spectrophotometer (Agilent Cary 60), fluorescence spectrophotometers (Hitachi F2700 and Fluoromax4), time-of-flight mass spectrometer for HRMS, and X-ray diffractometer (STOE STADI VARI PILATUS-100K). Materials included silica gel for chromatography, various aldehydes, bases, and solvents.

4：Experimental Procedures and Operational Workflow:

Condensation reactions were carried out by stirring mixtures of 4-aminopyrimidine N-oxides with aldehydes in basic conditions at 90-100°C for 1-6 hours under argon. Products were isolated via column chromatography and characterized by NMR, HRMS, UV-vis, and fluorescence spectroscopy.

5：Data Analysis Methods:

NMR spectra were analyzed using 2D techniques, fluorescence quantum yields were determined relative to standards, fluorescence decays were analyzed using nonlinear fitting, and computational studies were performed using Gaussian 09 with DFT and TDDFT methods.