Intramolecular Charge Transfer Photoemission of a Silicon-Based Copolymer Containing Carbazole and Divinylbenzene Chromophores. Electron Transfer Across Silicon Bridges

Abstract

A new copolymer consisting of N-isopropylcarbazole/dimethylsilylene bridge/divinylbenzene units was synthesized and characterized. Dual fluorescence was observed in this copolymer in polar solvents. The absence of the second band at the lower transition energy of the two emission maxima in nonpolar solvents and the quantitative correlation of the lower-energy emission band maxima with solvent polarity indicate that the lower-energy emission band arises from an intramolecular charge transfer (ICT) state. A series of model compounds was synthesized to investigate the source of the charge transfer. It was found that the Si-bridged dyad with a single N-isopropylcarbazole and a single divinylbenzene was the minimum structure necessary to observe dual luminescence. The lack of dual luminescence in low-temperature glasses indicates that the ICT requires a conformation change in the copolymer. Analogous behavior in the Si-bridged dyad suggests that the ICT in the copolymer is across the silicon bridge. Results from time-resolved luminescence measurements with picosecond and subnanosecond excitation were used to support the thesis that twisted charge-transfer states are the likely source of the observed dual luminescence.

Early Events in the Photoinduced Electron Transfer between Carbazole and Divinylbenzene in a Silylene-Bridged Donor–Acceptor Compound

“…The lifetime of the S 1 state of compound 1a in argon-saturated acetonitrile solution was determined in the ns-TCSPC experiment from a single-exponential fit. It was τ f = 15.3 ns, which is the same as the S 1 state lifetime of carbazole.…”

“…All of the femtosecond experiments reported in this paper were performed in a 3000 ps time window. For this reason, nanosecond lifetimes of the S 1 states are taken for better accuracy from the nanosecond time-resolved fluorescence measurements with detection based on a time-correlated single-photon-counting technique (TCSPC) …”

“…Steady-state absorption spectra of compounds 1 , 1a , and 1b in acetonitrile. (Absorption spectrum of compound 1 is displayed as a least-squares fit to the sum of spectra 1a and 1b ) …”

“…Therefore, it is attributed to the decaying ICT state. In the paper focused on the emission of compound 1 in acetonitrile (ACN), the ICT decay time was reported to be 20.4 ns. This discrepancy is caused by the fact that the fs-LFP and ps-TCSP experiments were performed in acetonitrile solutions with and without oxygen, respectively.…”

“…Compounds 1 , 1a , and 1b were synthesized using the methods described in ref and purified using high-performance liquid chromatography (HPLC). The HPLC measurements were performed on a Waters 600E multisolvent delivery system pump equipped with a Waters 996 photodiode array UV–vis detector.…”