Stacked nanocarbon photosensitizer for efficient blue light excited Eu(III) emission

Photosensitizer design to allow effective use of low-energy light is important for developing photofunctional materials. Herein, we describe a rational photosensitizer design for effective use of low-energy light. The developed photosensitizer is a stacked nanocarbon based on a rigid polyaromatic framework, which allows efficient energy transfer from the low-energy T1 level to the energy acceptor. We prepared an Eu(III) complex consisting of a luminescent center (Eu(III)) and stacked-coronene photosensitizer. The brightness of photosensitized Eu(III) excited using low-energy light (450 nm) is more than five times higher than the maximum brightness of previously reported Eu(III) complexes.


Supplementary Note 1 (Structural analysis)
The continuous shape measure factor S was calculated to estimate distortion degree of the coordination structure in the first coordination sphere based on the crystal structure data.
The The exciton coupling strength between two molecules is expressed as Supplementary  The emission decay curves of Eu(III) complex (2) and (3)

Supplementary Note 6 (Eu(III) emission excited by a blue light)
The development of red phosphors excited by a blue LED is required to fabricate highefficiency white LEDs. Recently, the efficient red luminescence of a brick-type Eu(III) complex excited by a blue LED was achieved for the first time. 5

Supplementary Note 7 (Energy transfer analysis using LUMPAC)
To obtain a deeper understanding of excited state dynamics for complexes 3 and 2, we calculated the energy transfer rates between ligands and Eu(III) ions using LUMPAC software. 8 The ground-state coordination geometries of the Eu(III) complexes 2 and 3 as isolated molecules (vacuum condition) were calculated using the Sparkle/RM1 model.
We used the optimized structure of complex 2 and 3 to estimate the singlet and triplet excited states with the configuration interaction singles (CIS) method based on the intermediate neglect of differential overlap/spectroscopic (INDO/S) technique, as proposed in previous reports. [8][9][10][11][12][13] The calculations were performed using ORCA software (v.4.2.0). 14 We used a point charge (+3) to represent the trivalent europium ion. The S1 energies of 3 and 2 were estimated to be 31,500 and 25,700 cm -1 , respectively. The T1 energies of complexes 3 and 2 were estimated to be 20,100 and 18,900 cm -1 , respectively.
We also calculated the energy transfer rates from singlet states using the singlet energy calculated by DFT calculation at the B3LYP level (6- 31G(d, p)). [15][16] The S1 energy is estimated to be 29500 cm -1 , and the calculated energy transfer rates from singlet state to 5 D4 and 5 D4 to singlet state are 2.8 × 10 4 and 7.8 × 10 -9 s -1 , respectively. The results indicate that energy transfers from S1 state are ineffective. On the other hand, the energy transfer rates from T1 to 5 D1, T1 to 5 D0, 5 D1 to T1, and 5 D0 to T1 are 3.1 × 10 6 , 3.9 × 10 6 s -1 , 2.1 × 10 4 , and 6.0 s -1 , respectively. The results indicate that energy transfers from T1 state are effective. These calculations also indicate that the back energy transfer from the Eu(III) ion to ligands is suppressed by the high T1 energy level (Fig. 1a) LMCT band with low energy (ca. 25,000 cm -1 ) has been shown to affect the electronic character of 4f-4f excited states. 17 We propose that the LMCT perturbation might account for some of the inaccuracy in the calculations.

Supplementary Note 8 (Temperature dependent emission lifetime of 5)
Temperature-dependent emission lifetimes were measured for Gd(III) complex (5) in 2-Me-THF. We used Arrhenius plots of these measurements to estimate the T1 lifetime of 5 at 300 K (Supplementary Figure 11, 145 K-163 K) as reported. 18 We have assumed that the decay rate does not change below 100 K (t = 6.2 s), as a similar decay rate is observed at 100 K and 110 K. The estimated T1 lifetime at 300 K is 40 ms, which is approximately 50 times longer than the Eu(III) emission lifetime.