화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.119, No.32, 8630-8642, 2015
Highly Emissive Whole Rainbow Fluorophores Consisting of 1,4-Bis(2-phenylethynyl)benzene Core Skeleton: Design, Synthesis, and Light-Emitting Characteristics
To create the whole-rainbow-fluorophores (WRF) having the small Delta lambda(em) (the difference of Delta lambda(em) between a given fluorophore and nearest neighboring fluorophore having the same core skeleton) values (<20 nin) in full visible region (lambda(em): 400-650 nm), the high log epsilon (>4.5), and the high phi(f) (>0.6), we investigated molecular design, synthesis, and light-emitting characteristics of the pi-conjugated molecules (D/A-BPBs) consisting of 1,4-bis(phenylethynyObenzene (BPB) modified by donor groups (OMe, SMe, NMe2, and NPh2) and an acceptor group (CN). As a result, synthesized 20 D/A-BPBs (1a-5d) were found to be the desired WRF. To get the intense red fluorophore (phi(f) > 0.7, lambda(em) > 610 nm), we synthesized new compounds (5e-51) and elucidated their photophysical properties in CHCl3 solution. As a result, 5h, in which a 4-cyanophenyl group is introduced to the para-position of two benzene rings in the terminal NPh2 group of Scl, was found to be the desired intense red fluorophore (log epsilon = 4.56, phi f = 0.76, Aem = 611 nm). The intramolecular charge-transfer nature of the S, state of WRF (1a-5d) was elucidated by the positive linear relationship between optical transition energy (v(em)) from the S, state to the So state and HOMO(D) LUMO(A) difference, and the molecular orbitals calculated with the DFT method. It is demonstrated that our concept (phi(f) = 1/(exp( A(pi)) + 1)) connected with the relationship between Of and magnitude (A(pi)) of it conjugation length in the S, state can be applied to WRF (1a-5c1). It is suggested that the prediction of Of from a structural model can be achieved by the equation phi(f) = 1/(exp( (nu) over tilde (a) - (nu) over tilde)(1/2) x a(3/2) + 1), where v(a) and nu(f) are the wavenumber (cm') of absorption and fluorescence peaks, respectively, and a is the calculated molecular radius. From the viewpoint of application of WRF to various functional materials, the light-emitting characteristics of la Si in doped polymer films were examined. It was demonstrated that la Si dispersed in two kinds of polymer film (PST and PMMA) emit light at the whole visible region and have the small Delta lambda(em) values (<20 nrn) and the high Of values (>0.6). Therefore, the present D/A-BPBs can be said to be the desired WRF even in the doped polymer film.