Synthesis, photophysical properties, and two-photon absorption behavior of pyrimidinyl urea derivatives

• Two microwave-assisted routes afford all-E pyrimidinyl ureas efficiently • Protonation modulates ICT and enhances fluorescence in moderate donors • Strong donor systems exhibit proton-induced nonradiative decay • Selected protonated species reach σ₂ values up to ∼1600 GM • Demonstrates tunable proton-switchable nonlinear optical response A new family of unsymmetrical N -pyrimidinyl- N ′-aryl/sulfonyl ureas incorporating a 4,6-distyrylpyrimidine chromophore was synthesized via two microwave-assisted strategies that alternate the order of urea formation and styryl installation. All products were isolated as the all - E isomers. In CH₂Cl₂, most derivatives absorb near 390 nm, while strong donor substitution (R 3 = NMe₂) induces a pronounced red shift. Protonation with trifluoracetic acid (TFA) generally enhances fluorescence (Φ F up to 0.41) and induces bathochromic shifts of up to ∼100 nm or more, except in the most intense push–pull systems, which undergo emission quenching. In the solid-state, the emission extends into the deep red/near-infrared (NIR) region (up to 755 nm) for high-donor-strength derivatives. Time-resolved studies reveal lifetime elongation upon protonation for moderate donors, but shortening for stronger ones. Two-photon absorption cross sections exceed 1000 GM (maximum ≈ 1600 GM) for some protonated derivatives, whereas the NMe 2 -substituted compound 2f remains highly active in its neutral form. These results demonstrate proton-switchable photophysical and NLO properties, offering a versatile platform for responsive optical materials.