SPECTROSCOPY AND PHOTOPHYSICS OF TETRAALKYLDIBENZOPORPHYCENES

Two recently synthesized derivatives of porphycene, 2,7,12,17-tetramet hyl-3,6-13,16-dibenzo porphycene and a-tert-butyl-3,6-13,16-dibenzo[cd e,mno]porphycene, were studied by stationary and time-resolved spectro scopy and quantum chemical calculations. Both compounds were found to be nonluminescent even at low temperatures. Picosecond transient absor ption studies performed in solution at 293 K and in solid nitrogen mat rices at 15 K revealed a rapid recovery of the ground-state bleaching. The rate of this process remains very high even at low temperatures. Possible reasons for this photophysical behavior are discussed, includ ing nonplanarity and a fast excited-state cis-trans NH tautomerization . Electronic transitions of dibenzoporphycenes may be correlated with those of porphyrin and porphycene. However, an ''intruder'' state lies between the analogues of the Q and Soret bands.