Phosphorescence of pi-conjugated oligomers and polymers.

We observed phosphorescence from a ladder-type poly-(para-phenylene) and an analogous oligomer containing five phenylene rings. The spectra are similar to the intrinsic fluorescence spectra and bear out a singlet-triplet splitting of 5000 cm(-1) (polymer) and 6800 cm(-1) (oligomer). Phosphorescence decay of the polymer occurs on a 10-100-micros scale obeying a power law and suggestive of nonradiative quenching, while that of the oligomer is asymptotically exponential with an intrinsic decay time of approximately 250 ms. The polymer also exhibits delayed fluorescence. It originates from delayed recombination of geminate electron-hole pairs rather than from triplet-triplet annihilation.

[Fine structure luminescence of etio-, copro- and mesoporphyrin following selective laser excitation]. / Tonkostrukturnaia liuminestsentsiia étio-, kopro- i mezoporfirina pri selektivnom lazernom vozbuzhdenii.

Fluorescence line spectra of etio- and coproporphyrin isomers and mesoporphyrin IX, as well as their ionic forms have been obtained and investigated using a tunable dye laser excitation (T = 4.2 K). Normal vibrational frequencies in the ground electronic state of both the neutral molecules and their ions have been determined. By comparing the line spectra of different porphyrins and their isomers the distinctions have been revealed which may be used for the identification of these compounds in solutions. Changes have been discovered in the coproporphyrin ion spectra in different solvents.

[Fine structure of the fluorescence spectra of chlorophyll a, protochlorophyll, and their pheophytins following selective laser irradiation]. / Tonkaia struktura spektrov fluorestsentsii khlorofilla a, protokhlorofilla i ikh feofitinov pri selektivnom lazernom vozbuzhdenii.

Fine structure fluorescence spectra of solutions in diethyl ether of chlorophyll a, pheophytin a, protochlorophyll and protopheophytin were obtained and studied at 4.2 K under stimulation with reconstructed laser on dyes. Dependence of the spectrum on lambda excit was studied and oscillation frequencies in basic and excited electron states were determined. Frequency dependence on the character of molecular surrounding was exemplified by chlorophyll a.