Charge-Transfer Fluorescence of Phenylpyrrole (PP) and Pyrrolobenzonitrile (PBN) in Cryogenic Matrices Energy Deformation 0,0 line 290nm 292 nm CT emission LE CT PBN emission in neat Ar matrix is of LE bands (at high frequencies) superimposed on a broad CT background. The LE emission includes 2 vibronic progressions due to 2 different trapping sites. One progression is blue-shifted by 446 cm -1 relative to the jet whereas the other is blue-shifted by only 86 cm -1. The minimal frequency of the 0,0 transition in the matrix is therefore 34,510 cm -1, which corresponds to 290 nm. Since fluorescence of PBN in neat Ar matrix is observed upon excitation at energies lower than the LE 0-0 band (at the absence of “ hot lines ” ) it is concluded that the CT state can be populated directly by light absorption, and not only via the LE state. Fluorescence spectra of PP (5) an PBN (6) in AN doped Ar matrix, in various excitation wavelengths ( exc ). PBNPP A slight effect compared to other polar media. 2 bands: normal LE band and a shifted CT band. A Slight shift  narrow distribution of sites. Strong dependence of the intensities of the 2 bands DF is observed in both PP and PBN in matrices. CT is therefore possible in cryogenic temperatures and under the motional restrictions in this rigid environment. The different photo-physical behavior of PP and PBN in argon matrices was explained in terms of the “matrix wall” model (see D. Schweke poster). PBN emits in AN-doped Ar from a strained adduct, shifted to the blue with respect to its spectrum in fluid systems, in which large amplitude motions are allowed. The global minimum of the A state of PBN in Ar matrix is lower than the B state, and can be directly populated by light absorption. in addition to its population by a non-radiative process from the B state.Conclusions Hagai Baumgarten, Danielle Schweke and Yehuda Haas Department of Physical Chemistry and the Farkas center for Light induced Processes The Hebrew University of Jerusalem, Jerusalem IsraelLiterature 1.D. Schweke, Y. Haas. J. Phys. Chem. A. 107 (2003) D. Schweke, H. Baumgarten, Y. Haas, W. Rettig and B. Dick. J. Phys. Chem. A. 109 (2005) T. Yoshihara, V.A. Galiewsky, I.S. Druzhinin, S. Saha, K.A. Zachariasse. Photochem. Photobiol. Sci. 2 (2003) L. Belau, Y. Haas and W. Rettig. J. Phys. Chem. A. 108, (2004). 5.S. Zilberg, Y. Haas.Phys. Chem. A.1 (2002) 106. Schematic energy level diagram of PP and PBN. The diagram describes the ICT process, which accounts for the appearance of dual emission. The A state surface includes two forms [5]: Quinoid and Anti- Quinoid. Doping effect exc PBNPP Broad CT emission LE vibronic bands LE emission Blue-shifted (Hypsochromic effect)   B <  X. 445 cm -1 Red-shifted (Batochromic effect)   B >  X. Emitting states LE shift relative to jet ResultsObjectives We studied the photo-induced Intramolecular Charge Transfer (ICT) of PP (N-Phenylpyrrol) [1] and PBN (4-(1H-pyrrol-1-yl)benzonitrile) [2] in cryogenic matrices by spectroscopic research of the Dual Fluorescence (DF) phenomenon. We performed fluorescence spectra and time resolved measurements in both neat and AN-doped Ar matrices. Our results are compared to previous studies of DF and ICT in solutions [3] and in gas phase [4]. The DF is due to two different excited states: LE (Locally Excited) labeled as the B state giving the normal emission and the CT (Charge Transfer) labeled as A state state giving an anomalous red-shifted emission. The ground state is labeled as X. PP and PBN belong to a family of para-substituted aromatic systems with Donor (D) and Acceptor (A) groups. Their fluorescence spectra exhibit a strong dependence on the environment polarity. The motivation to study the photo-physical properties of ICT in rigid matrices stems from their restrictions on the trapped molecules’ degrees of freedom: translation and rotation, including the torsion mode. Our goal was to find out whether ICT occurs in PP and PBN in the different matrices. The low temperature prevents the occurrence of barrier-dependent relaxation processes and the appearance of “hot” lines. Therefore the resulting spectra have a simple structure than in solutions. The low temperature also enables a long lifetime of the excited states. Fluorescence spectra of PP (3) and PBN (4) in neat Ar matrix, Cyclohexane (CH), Acetonitrile (AN) and jet-cooled spectra of the bare molecules, which allows the assignment of the LE spectrum, and the location of the 0,0 band. To the right: life-times measurements of PBN, supporting the assignment of the emission to 2 different excited states: LE and CT.Experimental 1 PC Photo- diode Prism array Sample Monochromator PMT Excitation beam Trigger Data Signal Fluorescence Movement control LASER Scope Matrix deposition system: planned to enable a delicate flow of the gas mixture onto the window which is held under low temperatures (down to 14K) and pressure. 2 Signal collection setup Gas Mix. Host Gas Needle Valve AN PBN Turbo Pump Rotation Pump Dewar Matrix Deposition PBN Heater He Cryostat Temp. Control Pressure gauge Valve Cold Window Gas mixture Guest Host 7 LE State Ground State CT State; Gas phase CT Fluorescence LE Fluorescence Absorption Quinoid Form Deformation (Torsion, Quinoidization) Energy 60 o 90 o 30 o 0o0o CT; Polar environment Anti-Quinoid Form Curve Crossing Abs. LE CT We thank Prof. B. Dick, Prof. W. Rettig, Dr. W. Fuss and Dr. K. Zachariasse for enlightening discussions. This research was supported by the Israel Science Foundation and by The Volkswagen-Stiftung (I/76 283). The Farkas Center for Light Induced Processes is supported by the Minerva Gesellschaft mbH.Acknowledgements PBN PP