Fluorescence microscopy of powder Spectroscopic properties ISTITUTO PER LO STUDIO DELLE MACROMOLECOLE Photoexcitation properties of films of the hydrated and anhydrous forms of 4-N,N-dimethylamino-4’-N’-methyl stilbazolium tosylate   J.-P. Bombenger (a), M. Cerminara (b), F. Meinardi (b), R. Tubino (b), E. Cariati (c), E. Tordin (c), R. Ugo (c), N. Casati (d), P. Macchi (d), A. Sironi (d), C.Botta (a) (a) Consiglio Nazionale delle Ricerche Istituto per lo Studio delle Macromolecole, via Bassini 15, 20133 MILANO, ITALY (b) Università di Milano, Dipartimento di Scienza dei Materiali, Via Roberto Cozzi 53, 20125 MILANO, ITALY (c) Università di Milano, Dipartimento di Chimica Inorganica, Metallorganica e Analitica, via Venezian 21, 20133 MILANO, ITALY (d) Università di Milano, Dipartimento di Chimica Strutturale e Stereochimica Inorganica, via Venezian 21, 20133 MILANO, ITALY Introduction 4-N,N-dimethylamino-4’-N’-methyl stilbazolium tosylate (DAST) is a high efficiency material for second harmonic generation (SHG) in its anhydrous form. The hydrated phase is centrosymmetric and consequently SHG inactive. Both phases present a structure compatible with J-aggregation. Fluorescence microscopy of powder Material Chemical structure 4-N,N-dimethylamino-4’-N-methyl stilbazolium tosylate Crystal structure Source: Follonier et al., J. Opt. Soc. Am., 19, 1990 (2002) Crystal structure….this is the anhydrous form what about the hydrated one????? Spectroscopic properties Absorption and fluorescence (lexc=457nm) spectra of films of the anhydrous and the hydrated phase Insert: photoluminescence excitation profile of the hydrated film at 725nm Piezochromism Evolution of the fluorescence (lexc=460nm) under prolonged manual crushing (grinding) Evolution of the fluorescence (lexc=460nm) under hydraulic pressure Evolution with the temperature of the fluorescence of a DAST hydrated film PL quantum yield of the DAST films: hydrated phase: 10%, anhydrous phase: 3% Conclusion The structural organization and the spectroscopic properties at room and low temperature prove that anhydrous and hydrated phases of DAST exhibit properties compatible with J-aggregation of the chromophores inside the structure. Two peaks are observed in photoluminescence: the high energy one is tentatively assigned to J-aggregate emission while work is in progress to assign the low energy one. An intriguing behaviour of the hydrated form is represented by its piezochromism of the luminescence. We thank Progetto CARIPLO “Nuovi materiali con nanoorganizzazione di cromofori in sistemi Host-Guest o su scaffold inorganico per dispositivi fotoluminescenti o optoelettronici”