The Constrution And Photophysical Process Investigation Of Flexibly Linked Triphenylamine-triazine D-A Systems

It's crucial controlling the charge-separation rate through molecular structure modification to achieve long-lived CS states for high performance in donor-acceptor?D-A?systems.A series of conjugated triphenylamine-trazine systems were constructed before in our group.It was confirmed that long lifetimes of CS states could be achieved through effective photo excitation in these novel systems which were used as the activative layer of organic solar cells farbrication.In this paper,alkyl chains with different length were introduced into typical D-A dyads MTPA-TRC to form three new flexibly linked triphenylamine-trazine D-A systems MTPA-TRC-n?n=1,2,3,n stands for the number of methylene units?.The construction strategy and photophysical process were thoroughly investigated.During the synthesis of MTPA-TRC-n,a series of reductive substrates with different N groups were designed to obtain the saturated alkyl chain decorated amino derivatives.Then quantum chemical calculation was adopted to explore the influence of intramolecular charge transfer?ICT?effect on the choice of reduction methods.The results reveal that ICT effect will facilitate the direct reduction of nitro and oxime group.However,ICT effect will damp the reduction of nirostyrene and cynostyrene group on account of that the polar double bonds need to be reducted firstly.The ortho double bond of nitro group can be efficiently reducted with sodium borohydride at-5?.Whereas reduction of the ortho double bond of cyano group requires lithium boronhydride at 80?for as long as 10 h.The photo-induced electron transfer process was investigated through spectral analysis and electrochemical method as well as chemical calculation with Gaussian09package.As long as milliseconds CS lifetime resulted from electron transition from donor moiety to acceptor moiety in these D-A systems were obtained.Accompany with Marcus charge transfer theory,the relationship between chemical structures and charge transfer process was established.The results show that the solvent reorganization energy is reduced by the alkyl chain but not sensitive to the chain length.However,electronic coupling matrix is obviously reduced due to the interruption of linkage conjugation and decresed along with the increasing bridge length.Additionally,the decay coefficient???of length dependence on electron transfer rate decreased from 0.4?^-1 to 0.3?^-1 in methanol in comparison with acetonitrile.It reveals that electron coupling between the donor and acceptor could be enhanced by the increased solvent polarity for the non-conjugated linked D-A systems.This work provides us the practical blueprint to obtain long-lived and high efficiency CS states with alkyl chain as the linkage for simple and small D-A systems.