This case study on a series of monomeric, dimeric and polymeric Cu I chlorido NHC-picolyl complexes shows that cuprophilic interactions can ensure strong spin-orbit coupling for fast (reverse)intersystem-crossing T 1 2 S 1 and T 1 -S 0 , and therefore can serve as a design motif for the construction of highly efficient Cu I -based TADF or T 1 emitters.Luminescent molecules showing thermally activated delayed fluorescence (TADF), i.e. thermally induced reverse intersystemcrossing (RISC) T 1 -S 1 with subsequent emission from the singlet excited state S 1 -S 0 , have proven to be particularly suitable materials for OLEDs and other photonic applications, as they are able to bypass the spin-forbidden phosphorescence T 1 -S 0 . [1][2][3] In this regard, Cu I complexes with a d 10 configuration have gained a lot of attention in the last 5 years, as the absence of metal centred d-d* transitions, leading to nonradiative decay, in combination with TADF makes them competitive to Ir III -and Pt II -based emitters. [4][5][6][7][8][9][10][11][12][13][14][15][16] Although some structure-property relationships have been formulated, [17][18][19] TADF in copper complexes is still difficult to predict a priori, let alone to design TADF materials, as it is an excited state property. In contrast, cuprophilic interactions can be prearranged in the ground state by careful choice of the ligand environment, and they have been shown to allow, albeit inefficiently, phosphorescence in simple dinuclear Cu I complexes with bridging diphosphines and other systems, 20-23 and also in clusters. [24][25][26] A few dicopper(I) complexes with short Cu-Cu contacts (o2.8 Å) have been reported to emit efficiently via TADF, but the influence of cuprophilic interactions in those has yet not been addressed. 4,8,19,[27][28][29] In this case study on a family of new bidentate copper(I) NHC-picolyl complexes we show that cuprophilic interactions can greatly enhance the radiative rate constants of the T 1 state by increasing spin-orbit coupling (SOC), giving emission lifetimes comparable to TADF, and can even be involved in the luminescence mechanisms when TADF is present. Thus, cuprophilic interactions provide a design methodology for highly efficient Cu I emitters.For this study, we have prepared a series of Cu I NHC-picolyl complexes (1-7, Fig. 1) by a facile one-step silver-free procedure from azolium chlorides in aqueous ammonia as basic and copper complexing medium (see ESI †). 30 The azolium salts include new picolyl linkers, functionalized in the para position Fig. 1 Chemical structures of complexes 1-7, for dimers representative molecular structure of 1 obtained from X-ray diffraction and intermolecular Cu-Cu distances of 1-4.