Supplementary Material (ESI) for PCCP This journal is © the Owner Societies 2009 List of 16 lowest lying triplet and singlet excited states for low-spin [Fe(btpa)]+2 cation calculated by means of TD DFT with use of B3LYP functional Excitation energies and oscillator strengths: Excited State 1: Triplet-B 1.2450 eV 995.83 nm f=0.0000 101 ->130 -0.10353 112 ->130 -0.21087 114 ->120 0.11220 114 ->128 0.18751 114 ->130 -0.92302 116 ->129 0.10315 Excited State 2: Triplet-A 1.2999 eV 953.79 nm f=0.0000 98 ->129 -0.13743 114 ->129 0.17657 115 ->118 0.15806 115 ->121 0.10079 115 ->129 0.84391 116 ->130 -0.33606 Excited State 3: Triplet-B 1.3910 eV 891.32 nm f=0.0000 114 ->130 0.10557 115 ->128 0.10269 115 ->130 -0.50384 116 ->118 0.13361 116 ->129 0.74089 Excited State 4: Triplet-A 1.6808 eV 737.64 nm f=0.0000 112 ->129 0.19370 114 ->118 0.15781 114 ->129 0.80571 115 ->129 -0.15828 116 ->117 0.12399 Excited State 5: Triplet-B 1.8318 eV 676.83 nm f=0.0000 98 ->130 -0.10068 115 ->117 -0.12625 115 ->128 -0.13821 115 ->130 0.66977 116 ->118 0.11038 116 ->129 0.45390 Excited State 6: Triplet-A 1.8572 eV 667.59 nm f=0.0000 115 ->129 -0.28399 116 ->117 0.25097 116 ->119 0.10305 116 ->120 0.10261 116 ->128 0.14859 116 ->130 -0.71724 Excited State 7: Triplet-A 2.1311 eV 581.79 nm f=0.0000 114 ->129 -0.10479 116 ->117 0.67085 116 ->119 0.25518 116 ->130 0.26237 Excited State 8: Triplet-B 2.2272 eV 556.68 nm f=0.0000 109 ->117 0.22214 109 ->119 -0.10928 115 ->117 0.64819 115 ->119 0.17971 115 ->130 0.14739 116 ->118 -0.11682 116 ->121 0.10138 Excited State 9: Singlet-B 2.3214 eV 534.09 nm f=0.0011 112 ->130 -0.12554 114 ->117 0.26065 114 ->128 0.12343 114 ->130 -0.58439 115 ->117 0.12333 115 ->130 -0.10703 116 ->129 0.15423 Excited State 10: Singlet-A 2.3491 eV 527.80 nm f=0.0013 114 ->129 0.10023 115 ->118 0.17174 115 ->129 0.59209 116 ->117 0.10619 116 ->130 -0.29965 Excited State 11: Singlet-B 2.4023 eV 516.10 nm f=0.0017 114 ->130 0.21063 115 ->117 0.15571 115 ->130 -0.32925 116 ->118 0.13873 116 ->129 0.53036 Excited State 12: Singlet-B 2.5421 eV 487.73 nm f=0.0031 114 ->130 0.11048 115 ->117 0.64381 115 ->119 0.10073 116 ->129 -0.18873 Excited State 13: Singlet-B 2.5692 eV 482.58 nm f=0.0003 114 ->117 0.60531 114 ->119 0.12977 114 ->130 0.23690 115 ->117 -0.12816 115 ->130 -0.13356 Excited State 14: Singlet-A 2.6998 eV 459.24 nm f=0.0303 114 ->129 0.18420 115 ->118 0.16293 115 ->129 -0.14954 116 ->117 0.61826 Excited State 15: Singlet-A 3.2198 eV 385.06 nm f=0.0063 114 ->118 0.33214 114 ->129 0.35304 115 ->118 0.18788 116 ->117 -0.21834 116 ->119 0.32835 Excited State 16: Singlet-A 3.2615 eV 380.14 nm f=0.0000 114 ->118 0.33743 115 ->118 -0.22690 115 ->129 -0.16618 116 ->120 0.24059 116 ->130 -0.41633