Amplified emission of phthalocyanine isolated in cryogenic matrices

Abstract

Laser induced fluorescence spectroscopy of free-base (H 2 Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices reveals a quite unexpected phenomenon with a moderate increase in the laser intensity. In all matrices except Xe, a huge increase occurs in the intensity of an emission band near 755 nm when pumping the S 1 ' S 0 transition. The band involves a vibrational mode of the ground state, located at 1550 and 1525 cm À1 for H 2 Pc and ZnPc, respectively. Many of the characteristics of amplified emission (AE) are exhibited by this vibronic transition. Excitation scans recorded for the AE band yield greatly enhanced site selectivity compared to what is obtained in normal fluorescence excitation scans.

Electronic spectroscopy, stimulated emission, and persistent spectral hole burning of cryogenic nitrogen matrices doped with tetrabenzoporphin

“…The present work is in continuation of previously published results [7,8] in which the authors discussed the occurrence of the phenomenon of SE in H 2 Pc, ZnPc and H 2 TBP molecules isolated in cryogenic matrices of rare gases, identifying so far a number of unsolved problems. For instance, a necessity arises to clarify the role of different parameters on the stimulated emission phenomenon by changing the nature of the host matrix, then changing the electron-phonon interaction.…”

“…We have performed spectroscopic studies of free base phthalocyanine (H 2 Pc) and its zinc counterpart (ZnPc) [7], as well as of free base tetrabenzoporphin (H 2 TBP) [8] in matrices of rare gases (Ne, Ar, Kr, Xe) at low temperature (8 K). We found that under the action of a pulsed laser excitation, SE was observed in guest molecules in these matrices and corresponds to transitions between the lowest singlet state S 1 to specific vibrational levels of the ground electronic state S 0 (S 1 (0-0) → S 0 (0-1) transition).…”

Infra-red and Raman spectroscopy of free-base and zinc phthalocyanines isolated in matrices

“…4 Recently, with the use of only moderately intense laser excitation we observed amplified emission (AE) of zinc (ZnPc) and freebase phthalocyanine (H 2 Pc) isolated in rare gas and nitrogen matrices. 5 Because this effect was observed in thin samples (o100 mm) without the use of feedback optics, the Pcs are revealed as systems with extremely high optical gain. The mode exhibiting AE is a fluorescence transition from the vibrationless level of the first excited electronic state S 1 to a specific vibrationally excited level of the ground S 0 state.…”

“…Due to the similar energy splitting between the Q X and Q Y states in matrix spectra and the assumed transition energy of the N-H in-plane bending vibration, this mode is considered to be important in the coupling between the two electronic states. 8 Since the vibrational modes in the ground S 0 state and the first excited Q (S 1 ) state are very similar, 9,10 vibrational assignments in the ground state are essential for analysing the complex vibronic structure in the electronic excitation spectra. As a precursor to an analysis of the excitation and emission spectra, which will be presented in a forthcoming article, 10 an analysis of the fundamental vibrational modes is required and undertaken herein.…”

“…Large basis set DFT calculations were performed on the four aforementioned molecules in order to assign the observed vibrational modes. These calculations are essential for assignments of the vibrational modes present in both Raman scattering and visible fluorescence spectra recorded previously by our group 5 with Q-band excitation of matrixisolated Pcs.…”