A tris-bipyridyl complex of the general formula I: wherein M is Fe; n is the formal oxidation state of the transition metal, wherein n is 2 or 3; X is a counter anion PF 6 -; m is 2 or 3; R 1 to R 18 each is H; and A 1 to A 6 each independently is a group of the formula III, wherein R x is H, or formula IV, wherein R y is H, linked to the ring structure of the complex of general formula I via R 19 wherein A 1 to A 6 each is a group of formula III, and (i) R 19 each is H 2 C-CH 2 and the complex is selected from 2SB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2SB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate); (ii) R 19 each is HC=CH and the complex is selected from 2DB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethenyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2DB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethenyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate); or (iii) R 19 each is C≡C and the complex is selected from 2TB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethynyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2TB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethynyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate), or wherein A 1 to A 6 each is a group of formula IV, and (i) R 19 each is H 2 C-CH 2 and the complex is selected from 4SB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4SB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate); (ii) R 19 each is HC=CH and the complex is selected from 4DB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethenyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4DB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethenyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate); or (iii) R 19 each is C≡C and the complex is selected from 4TB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethynyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4TB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethynyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate). M is Fe; n is the formal oxidation state of the transition metal, wherein n is 2 or 3; X is a counter anion PF 6 -; m is 2 or 3; R 1 to R 18 each is H; and A 1 to A 6 each independently is a group of the formula III, wherein R x is H, or formula IV, wherein R y is H, linked to the ring structure of the complex of general formula I via R 19 wherein A 1 to A 6 each is a group of formula III, and (i) R 19 each is H 2 C-CH 2 and the complex is selected from 2SB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2SB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate); (ii) R 19 each is HC=CH and the complex is selected from 2DB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethenyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2DB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethenyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate); or (iii) R 19 each is C≡C and the complex is selected from 2TB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethynyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2TB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethynyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate), or wherein (i) R 19 each is H 2 C-CH 2 and the complex is selected from 2SB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2SB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate); (ii) R 19 each is HC=CH and the complex is selected from 2DB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethenyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2DB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethenyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate); or (iii) R 19 each is C≡C and the complex is selected from 2TB(Fe 2+) [tris[4,4'-bis(2-(4-pyridyl)ethynyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 2TB(Fe 3+) [tris[4,4'-bis(2-(4-pyridyl)ethynyl)-2,2'-bipyridine]iron] tris(hexafluoro-phosphate), or wherein A 1 to A 6 each is a group of formula IV, and (i) R 19 each is H 2 C-CH 2 and the complex is selected from 4SB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4SB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate); (ii) R 19 each is HC=CH and the complex is selected from 4DB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethenyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4DB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethenyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate); or (iii) R 19 each is C≡C and the complex is selected from 4TB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethynyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4TB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethynyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate). (i) R 19 each is H 2 C-CH 2 and the complex is selected from 4SB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4SB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate); (ii) R 19 each is HC=CH and the complex is selected from 4DB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethenyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4DB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethenyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate); or (iii) R 19 each is C≡C and the complex is selected from 4TB(Fe 2+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethynyl)-2,2'-bipyridine]iron] bis(hexafluoro-phosphate) or 4TB(Fe 3+) [tris[4,4'-bis(2-(4-pyrimidinyl)ethynyl)-2,2'-bipyridine] iron] tris(hexafluoro-phosphate).