THE T1 RAMAN-SPECTRA OF BACTERIOCHLOROPHYLL-A - CHANGES IN THE BOND ORDERS OF THE CONJUGATED MACROCYCLE UPON TRIPLET EXCITATION

The T1 Raman spectra of bacteriochlorophyll a (BChl) are reported for the first time. One-color, simultaneous pump-and-probe measurement using the 457.9, 430 and 420 nm nanosecond pulses as well as two-color, pump-and-probe (delay 1 μs) measurement using the 337 nm (pump) and 420 nm (probe) nanosecond pulses gave rise to essentially the same spectra showing Raman lines around 1584, 1478, 1407, 1320, 1187 and 1093 cm-1. Comparison of the Raman frequencies between the S0 and T1 states revealed that the bond-orders of the "double bonds" ("single bonds") in the conjugated macrocycle decrease (increase) upon triplet excitation. © 1990.