Ultrafast Dynamics of Metal Complexes of Tetrasulfonated Phthalocyanines at Biological Interfaces: Comparison between Photochemistry in Solutions, Films, and Noncancerous and Cancerous Human Breast Tissues

A promising material in medicine, electronics, opto-electronics, electrochemistry, catalysis, and photophysics, Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS4) is investigated at biological interfaces of human breast tissue by means of steady-state and time-resolved pump-probe spectroscopies: IR, Raman, UV-vis, fluorescence, and electronic transient absorption by pump-probe spectroscopy. Spectrally resolved pump-probe data were recorded on time scales ranging from femtoseconds to nanoseconds and give insight into molecular interactions and primary events in the interfacial region. The nature of these fast processes and pathways of the competing relaxation processes from the initially excited electronic states in AlPcS4 films and at biological interfaces of human breast cancerous and noncancerous tissues is studied. Comparison between photochemical dynamics in the biological environment of the human breast tissues and that occurring in aqueous solutions is presented. The excited-state absorption (ESA) decays and bleaching recovery of the ground state have been fitted in the time window extending to nanoseconds (0-1 ns). We found that the excited-state dynamics of AlPcS4 at biological interfaces of human breast tissue is extremely sensitive to the biological environment and differs drastically from that observed in solutions and films. We demonstrated that the ultrafast dynamics at biological interfaces is described by three time constants in the ranges of 110-170 fs, 1-7 ps, and 20-60 ps. We were able to ascribe these three time constants to the primary events occurring in phthalocyanine at biological interfaces. The shortest time constants have been assigned to vibrational wavepacket dynamics in the Franck-Condon region down to the local minimum of the excited-state S-1. The 1-7 ps components have been assigned to vibrational relaxation in the excited and ground electronic states. In contrast to the dynamics observed in aqueous solutions with the components in the range of 150-500 ps assigned to decay from S-1 to the ground electronic state, these slow components have not been recorded in human breast tissue. We have shown that the lifetimes characterizing the first excited-state S-1 in the interfacial regions of the breast tissue are markedly shorter than those in solution. It suggests that molecular structures responsible for harvesting of the light energy in biological tissue find their own ways for recovery through some special features of the potential energy surfaces such as conical intersections, which facilitate the rate of radiationless transitions. We found that the dynamics of photosensitizers in normal (noncancerous) breast tissue is markedly faster than that in cancerous tissue.