The person in charge of the research group in Lecce University graduated with first class honours in Chemistry at Pisa University in 1988. He became Researcher in 1992, Associated Professor in 2000 and Full Professor in January 2005. He spent, by CNR-NATO fellowships or other projects, research periods at the Chemistry Department of Manchester University, UK (Prof. P. Hodge), the Centre for Molecular Electronics of teh University of Durham, UK (Prof. M.C. Petty) the Centre for Advanced Materials Processing of Clarkson University, NY, USA (Prof. J. Fendler) and at Max-Planck-Institut fur Biophysikalische Chemie, Goettingegn, Ger (Prof. D. Moebius). In Italy, research stages were carried out in Pisa (Prof. L. Senatore) and Padua (Prof. L. Pasimeni). His main interests are in the field of deposition (especially via self-assembling methods, such as Layer-by-Layer, usual self-assembly, or Langmuir-Blodgett/Langmuir-Schaefer techniques), characterisation and possible applications (above all in chemical sensors or opto-electronic devices) of thin organic films. In this connection he has got particular competences in the study of floating films at the air-water interface through analysis of Langmuir curves (surface pressure vs. area per molecule), surface potential curves, Brewster Angle Microscopy, fluorescence microscopy and reflection UV-Vis spectroscopy directly at the air-water interface. The most used spectroscopic characterisation techniques of deposited films are: UV-Vis spectroscopy (also by polarised light) and FT-IR spectroscopy also in differential mode. The transduction techniques used in chemical sensor applications involve electrical, optical and piezo-electrical methods. The most investigated substances are macrocycles exhibiting wide conjugation, such as porphyrins, corroles and phthalocyanines, fullerene derivatives and their dyads and triads with porphyrins, conductive polymers. In this connection he has settled scientific collaborations with some national and foreign research groups, such as: Proff. J.A. de Saja and M.L. Rodriguez-Mendez (Valladolid Univ.), D. Möbius (MPI, Göttingen, GER), L. Brehmer (Potsdam Univ., GER), D. Guldi (Erlangen Univ., GER), M. Petty (Durham Univ., UK), D. Arnold (Brisbane Univ., AUS), J. Jiang (Shandong Univ., China), Y. Inoue and V. Borovkov (Osaka Univ., Japan).
Some of the most recent and innnovative researches in the group of Lecce are herewith reported. The observation that fullerene C60 can reversibly accept up to six electrons in solution has prompted us to use C60 derivatives as electron acceptors in photoinduced processes using the cheapest available energy from solar radiation. The first stage has been immobilisation of the active layer in order to subsequently construct a functioning device. Therefore, various C60 derivatives have been investigated in two different manners: covalently connected to strong donors (usually porphyrins) or in blends with them. In the first case, using a fulleropyrrolidine/Ru-porphyrin dyad, time-resolved (nanosecond) flash photolysis experiments have not revealed transient variations in the UV-Vis-NIR spectral interval, probably because the excited singlet state of fullerene undergoes rapid decay. To avoid such a drawback, a new strategy was adopted: to distribute dyad molecules in a matrix of arachidic acid in large excess. In this way the dyad molecules are sufficiently separated in order to prevent electronic communication and the processes of electronic transfer prevail over annihilation.
Then an innovative approach for the growth of active layers containing both C60 and porphyrin derivatives was suggested: a cationic fullerene derivative was spread onto an aqueous subphase containing a water-soluble anionic porphyrin. The coulombic interaction between the two substances was strong enough to allow their contemporaneous transfer onto solid supports by Langmuir-Schaefer technique. A thorough spectroscopic, morphological and structural characterisation has allowed to comprehend the properties of fabricated films, above all for photoinduced phenomena. At the moment we are investigating systems containing an amphiphilic porphyrin and a water-soluble fullerene derivative.
Another fruitful research subject concerns deposition and characterisation of multilayers of tetrapyrrolic derivatives, such as porphyrins, phthalocyanines, porphyrazines, porphyrinogens and corroles. Such macrocycles are very attractive in the light of their properties (resistance to strong chemical aggressive agents, thermal stability, high purity and remarkable technological applications, ranging from applications as dyes in dyeing plants to active moieties in chemical sensors or opto-electronic devices); the large electronic delocalisation is at the basis of many of the important applications of these macrocycles. We are presently studying conformational equilibria and chirality induction (via ligation with chiral amines) in bis-porphyrins directly at the air-water interface and the properties of corresponding films.
L. Valli is also author of more than 120 publications on scientific journals with international scientific committee. He has been also referee for various international scientific journals, such as Advances in Colloid and Interface Science, Journal of the American Chemical Society, Biosensors and Bioelectronics, Colloids and Surfaces A, IEEE Sensors Journal, Journal of Colloids and Interface Science, Journal of Physical Chemistry B, Journal of Porphyrins and Phthalocyanines, Langmuir, Journal of Materials Chemistry, Chemistry of Materials, Physical Chemistry Chemical Physics, Surface Science, Thin Solid Films. He was twice Guest Editor for Materials Science and Engineering C. He has taken part as an oral speaker to many international meetings, also as invited speaker. He has also participated to the organisation of International Meetings, such as The First International Workshop on “Thin Organic Films: Properties and Applications” (September 1996) and the VIII European Conference on Organised Thin Films (ECOF 8, September 2001); he is Chairman of the Advisory Committee of the European Conferences ECOF. He has got the organisation in 2007 of the National Conference of Physical Chemistry Division of the Italian Chemical Society. He has obtained fundings for many scientific programmes, such as: Fondo Integrativo Speciale per la Ricerca (FISR), Accordo di programma Università di Lecce - Provincia di Lecce, Piani di potenziamento della Rete Scientifica e Tecnologica (Legge 488/297), Progetti PON, Cofin, Programmi INTERREG, Vigoni.
He teaches for students in the Faculties of Science, Engineering and Cultural Heritage and was the tutor for more than 60 thesis.