We report on the first observation of reverse saturable absorption by ferrocene (Fc) in toluene using nanosecond pulses at 532 nm. Pump and probe experiments in the visible spectral region show the existence of an excited triplet state with an intersystem crossing quantum yield S1 --> T1 of 0.085 and a molar extinction coefficient epsilon(Fc)(T) of 5650 L mol(-1) cm(-1) at 700 nm. The full understanding of the nonlinear optical behavior of Fc cannot be obtained, however, with a model that includes only the one-photon absorption from T1, but it is mandatory to consider also a simultaneous two-photon absorption from an excited singlet state of Fc (two-photon absorption cross section: 2.4 x 10(-41) cm4 s ph(-1) mol(-1)). The optical spectrum of the ground and triplet state of Fc are calculated within a TD-DFT approach considering several functionals (PBE, BLYP, LDA, OPBE) for the optimization of molecular geometry.

A twisted intramolecular charge-transfer (TICT) process has been identified in (2-ferrocenyl)indene. This photochemical process explains the anti-Kasha's rule fluorescence emission observed for this system. Experimental and model investigations on (2-ferrocenyl)tetramethylindene and (2-ferrocenyl)-hexamethylindene were also performed, in order to evaluate the effect of a steric hindrance on the TICT mechanism. The energy of the lowest main excited states was computed with a TD-DFT approach, as a function of the rotation of the dihedral angle between the indene and the cyclopentadienyl planes. To the best of our knowledge, this is the first example of TICT generated by metal-to-ligand charge transfer (MLCT) in a ferrocene-containing complex and, more generally, the first case of complexes in which a metal center is directly involved.

Multiphoton absorptions are important non-linear optical processes which allow us to explore excited states with low energy photons giving rise to new possibilities for photoinduced processes. Among these processes, multiphoton absorptions from excited states are particularly interesting because of the large susceptibilities characteristic of excited states. Here we explore the nonlinear transmission measurements recorded with 9 ns laser pulses at 1064 nm of the radical cations of (2-ferrocenyl)indene and of (2-ferrocenyl)-hexamethylindene, two interesting very stable molecules. The non-linear transmission data can be interpreted with a multiphoton sequence of three photon absorptions, the first being a one photon absorption related to the intramolecular charge transfer and the second a two photon absorption from the excited state created with the first process. The two photon absorption cross section is found to be several orders of magnitude larger than those usually found for two photon absorbing systems excited from the ground state.

A new method based on ion chromatography (IC) was developed for the determination of phosphorus in fertilizers. Fertilizers were extracted with water, mineral acids, and 2% formic acid, 2% citric acid, and neutral ammonium citrate solutions according to European Regulation No. 2003/2003 of the European Parliament and the Council of October 13, 2003, or the Decree of the Italian Agriculture Minister of June 17, 2002; the extracts were analyzed by direct injection, after simple filtration, by IC on an IonPac AS19 (250 × 4 mm id) column, using a KOH (21-50-21 mM) gradient and suppressed conductivity detection. The calibration plot was linear over the range of 550 mg/L (r2 of >0.999). The method was evaluated by comparison with a gravimetric method according to established norms. Associated uncertainty at the 95% confidence level was established as 0.47% for the determination of 346% P2O5 by IC. A good chromatographic separation of phosphorus forms such as phosphates and phosphites, and some other important anions like nitrates, chlorides, and sulfates present in many commercial fertilizers was also possible, with a linear response over the range of 550 mg/L. After a more complete validation, this IC determination of phosphorus could replace more tedious methods such as those using gravimetric determinations.