Through-bond conjugation (TBC) and/or through-space conjugation (TSC) determine the photophysical properties of organic luminescent compounds. No systematic studies have been carried out to understand the transition from aromatic TBC to non-aromatic TSC on the photoluminescence of organic luminescent compounds. In this work, a series of small aromatic and aliphatic aldimines were synthesized. For the aromatic imines, surprisingly, N,1-diphenylmethanimine with the highest TBC is non-emissive, while N-benzyl-1-phenylmethanimine and N-cyclohexyl-1-phenylmethanimine emit bright fluorescence in aggregate states. The aliphatic imines are all emissive, and their maximum emission wavelength decreases while the quantum yield increases with a decrease in steric hindrance. The imines show concentration-dependent and excitation-dependent emissions. Theoretical calculations show that the TBC extents in the aromatic imines are not strong enough to induce photoluminescence in a single molecule state, while the intermolecular TSC becomes dominant for the fluorescence emissions of both aromatic and aliphatic imines in aggregate states, and the configurations and spatial conformations of the molecules in aggregate states play a key role in the formation of effective TSC. This study provides an understanding of how chemical and spatial structures affect the formation of TBC and TSC and their functions on the photoluminescence of organic luminescent materials.

Many nontraditional luminogens (NTLs) without any large π‐conjugated structures are reported to exhibit room‐temperature phosphorescence (RTP). Unfortunately, the reported NTLs mostly emit blue or green RTP. Achieving more redshifted RTP from NTLs remains a great challenge. Herein, a series of nonaromatic polymers exhibiting yellow and orange–red RTP are reported. Poly(itaconic anhydride) (PITA) does not exhibit RTP, its hydrolyzed product poly(itaconic acid) (PITAc) exhibits weak yellow RTP, but the ionized product poly(sodium itaconate) (PITANa) can emit stronger and redshifted RTP. Moreover, the ionized copolymers poly(vinyl pyrrolidone‐co‐sodium itaconate) (PIVPNa) and poly(vinyl pyrrolidone‐co‐sodium maleate) (PMVPNa), the mixture of PITANa/poly(vinyl pyrrolidone) (PVP), and the full hydrolyzed product of poly(vinyl caprolactam‐co‐sodium itaconate) (PIVCNa) all exhibit strong orange–red RTP emissions at ≈600 nm. Structural characterizations and theoretical calculations prove that hydrogen bonding and ionic bonds lead to the rigidification of polymer chain conformations, and more importantly, both intra‐ and interchain nonaromatic electron donor–acceptor (nDA) structures and hence through‐space charge transfer are formed between carboxylate and lactam groups in proper conformations, which facilitates the occurrence and redshift of RTP in NTLs. This work provides a novel strategy to design NTLs with redshifted RTP and improves the understanding of the photoluminescence mechanism of NTLs.

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Nontraditional luminogens (NTLs) do not contain any conventional chromophores (large π-conjugated structures), but they do show intrinsic photoluminescence. To achieve photoluminescence from NTLs, it is necessary to increase the extent of through-space conjugation (TSC) and suppress nonradiative decay. Incorporating strong physical interactions such as hydrogen bonding is an effective strategy to achieve this. In this work, we carried out comparative studies on the photoluminescence behaviors of two β-enamino esters with similar chemical structures, namely methyl 3-aminocrotonate (MAC) and methyl (E)-3-(1-pyrrolidinyl)-2-butenoate (MPB). MAC crystal emits blue fluorescence under UV irradiation. The critical cluster concentration of MAC in ethanol solutions was determined by studying the relationship between the photoluminescence intensity (UV–visible absorbance) and concentration. Furthermore, MAC exhibits solvatochromism, and its emission wavelength redshifts as the solvent polarity increases. On the contrary, MPB is non-emissive in both solid state and solutions. Crystal structures and theoretical calculation prove that strong inter- and intramolecular hydrogen bonds lead to the formation of large amounts of TSC of MAC molecules in aggregated states. No hydrogen bonds and thus no effective TSC can be formed between or within MPB molecules, and this is the reason for its non-emissive nature. This work provides a deeper understanding of how hydrogen bonding contributes to the luminescence of NTLs.