Design of near infrared (NIR) emissive lanthanides such as ytterbium (Yb), erbium (Er) and neodymium (Nd) attracts considerable attentions for the potential applications in telecommunications, optical materials and biological imaging. Exploring an appropriate antenna ligand with the lowest triplet excited state (T₁) to efficiently sensitize Ln emission plays a central role to overcome the forbidden f-f transition. To address this issue, natural light harvesting system sets a golden standard for harnessing sunlight power and energy transfer process with molecular precision. A prominent example is given by chlorophylls b, d, f widespread in land plants and cyanobacteria and algae of ocean, respectively, with gradually red shifted Q bands mainly differing from β-formyl substituent orientation. In contrast to modeling studies on deciphering how chlorophylls confer light harvesting function, much less has been reported regarding the application of such insights in designing luminescence materials.^1-4 In this work, we reported the significant effect, arising from subtle structural changes, on tuning energy transfer process from the triplet state (T₁) of ligand to Yb(III). Minor β-substituent orientation change in Yb cis/trans-porphodilactones (Yb-1 and Yb-2) significantly influences their NIR emissive properties that Yb-1 presented significant enhanced NIR luminescence and high thermo-sensitivity compared to Yb-2 (> 10 times). Combining with spectroscopy studies, we found strong back energy transfer process in Yb-1 but ineffective T₁ → Ln* energy transfer in Yb-2. The strategy learning from nature should open a new method for designing NIR functional lanthanide complexes.

1. X.-S. Ke, Y. Chang, J.-Z. Chen, J. Tian, J. Mack, X. Cheng, Z. Shen* and J.-L. Zhang*, J. Am. Chem. Soc., 2014, 136, 9598-9607;

2. X.-S. Ke, H. Zhao, X. Zou, Y. Ning, X. Cheng, H. Su*, and J.-L. Zhang* ,J. Am. Chem. Soc., 2015, 137, 10745-10752;

3. X.-S. Ke, B.-Y. Yang, X. Cheng, S. L.-F. Chan, and J.-L. Zhang, Chem. Eur. J., 2014, 20, 4324-4333;

4. X. S. Ke, J. Tang, J. J. Chen, Z. Y. Zhou, J.-L. Zhang*, ChemPlusChem, 2015, 80, 25, 237-252;