Long-lived photoexcited states in symmetrical polydicarbazolyldiacetylene

Long-lived photoexcited states in polydiacetylenes with different molecular and supramolecular organization

“…The experimental data could in fact be fitted only with a I 0.73 law. In contrast with previous results on other PDA's, 19 no linear relationship could here be found even taking into account only the measurements carried out in the low laser intensity range. This sublinear intensity dependence has been detected also for other polymers whose ⌬T versus dependence was fitted by a monomolecular decay law.…”

“…On the other hand, lifetime ratios of ͱ2 and ͱ3 are predicted for a bimolecular recombination kinetics since in this case the lifetime should vary as the inverse square root of the laser intensity. 17,19 At 20 K, the lifetime for either the red ͑135 s͒ and the blue ͑320 s͒ forms turns out to be very similar to those at 77 K, giving further support to the deep trapping of the nonlinear excitations in this polymer ͓Fig. 7͑c͔͒.…”

“…In both cases the band intensity corresponding to different laser powers is independent on the chopper frequency up to 200 Hz and then begins to roll off for higher frequencies. The fact that for both forms the knee position is practically independent on the laser power is unambiguously indicative of a monomolecular decay kinetics described by the equation 19 dn dt ϭG͑t͒Ϫ n . ͑1͒…”

“…The same behavior has been previously observed in other conjugated systems. 19,[36][37][38] Unfortunately we cannot discuss in detail the relation between photoexcited charged states and oscillations in the bleaching region because no electromodulated spectra of our polymers are so far reported. The PA spectra of the blend obtained with both the 457-and 514-nm exciting lines show features identical to those obtained with the 488-nm excitation.…”

“…Among these polymers, the polydiacetylenes ͑PDA's͒ have enjoyed a period of renaissance [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and the synthesis of novel PDA's has enlarged our knowledge on their properties, in particular, on the values of their nonlinear susceptibilities. 15,16 In the last five years we have been interested in the study of a class of attractive PDA's, the polycarbazolyldiacetylenes, 5,[17][18][19][20][21][22] in particular, of poly͓1,6-di ͑ N-carbazolyl͒-2,4-hexadiyne͔͑polyDCHD͒, 5,[19][20][21][22][23][24][25][26] which is, however, insoluble. With the aim of improving its processability we have prepared a modified polyDCHD by inserting long aliphatic chains on the carbazolyl side groups.…”