Click chemistry uses highly reactive building blocks such as azides and alkynes that, with copper ions as a catalyst, join in a short time and with excellent yields. Because it needs no strict stereocontrol or elaborate conditions, it streamlines the synthesis of drug candidates and polymers. Carolyn Bertozzi went a step further by inventing copper-free “bioorthogonal” reactions that proceed inside living systems. This made it possible to light up and track sugars and proteins in real time within cells and animals. The technology now aids in designing antibody–drug conjugates that target only cancer cells and in producing robust new materials. Improvements in everyday plastics and faster drug-development pipelines illustrate the research’s broad social benefits.

The quintessential click reaction, copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC), exhibits broad functional-group tolerance and furnishes 1,4-substituted 1,2,3-triazoles with exquisite selectivity. Morten Meldal discovered CuAAC serendipitously while screening solid-phase peptide libraries, whereas K. Barry Sharpless framed the reaction within a philosophy that values function over biomimetic complexity—coining the term “click.” Carolyn Bertozzi subsequently introduced strain-promoted azide–alkyne cycloaddition (SPAAC), which eliminates copper by incorporating cyclooctyne-based alkynes. SPAAC enabled live-cell glycan imaging and targeted drug delivery. Both CuAAC and SPAAC proceed in aqueous, near-physiological conditions and serve as “universal couplings” for protein modification, surface functionalization, and polymer post-processing. The resulting triazoles offer hydrogen-bonding and π-stacking capabilities beneficial for medicinal chemistry and advanced materials. From the standpoint of green chemistry, click reactions satisfy atom economy and benign-solvent criteria, further underscoring their significance.

CuAAC proceeds through a dinuclear copper acetylide intermediate, featuring an almost barrier-less concerted cycloaddition along the reaction coordinate. Tailored ligands accelerate the aqueous reaction to 10^3–10^5 M⁻¹ s⁻¹; THPTA and BTTAA are routinely employed in bioconjugation. SPAAC leverages ~19 kcal mol⁻¹ of ring strain in cyclooctyne derivatives to lower the activation energy and minimize off-target reactivity in vivo. Bertozzi has advanced site-specific antibody–drug conjugate (ADC) synthesis by integrating N-glycan engineering with click-installable enzymes, paving the way for clinical translation. Meldal exploited CuAAC for the combinatorial synthesis of poly-triazole–peptide hybrids, yielding high-affinity inhibitors and new SAR paradigms. In materials science, click-mediated “graft-to” strategies have produced block copolymers and surface-modified carbon nanotubes with enhanced dispersion and conductivity. Continuous-flow platforms that integrate CuAAC and SPAAC exemplify process intensification and are being adopted in active pharmaceutical ingredient manufacture. Collectively, these advances cement the click platform as a meta-technology spanning organic synthesis, chemical biology, and process engineering.