| The strained organic semiconductors are organic semiconductor materials with higher strain energy.Duo to this intramolecular strain energy,the materials exhibiting special electronic structures and photoelectric properties which have attracted not only synthetic but also theoretical chemist’s attention.Recently,many stained organic semiconductors have been reported and extensively researched.And fluorene exhibits inherent larger exciton binding energies and excellent charge delocalization,enabling it to be an important building block in the molecular design of the organic photoelectric materials.However,up to date,there are few reports on fluorene-based strained organic semiconductors.In order to further insight into get the steric strain effect on opto-electronic properties of these compounds,a series of fluorene-based strained organic semiconductors with different fluorene numbers（[n]CFs（n=3-8））were designed.The structure,strain energy and photoelectric properties of[n]CFs（n=3-8）were investigated.Compared with the corresponding linear oligomer,it is found that strain energy can lead to the HOMO energy levels increase and LUMO energy levels decrease.The energy gap become narrower.And then,modeling compound,[4]cyclo-9,9-dimethyl-2,7-fluorenylene(strain energy=79.8 kcal mol-1)was synthesized via two steps utilizing ligand exchange reaction and reductive elimination strategy.The Structure was confirmed by X-ray analysis.A green emission at 512 nm of[4]CF can be observed in solution,film and crystal states.The green emission at 512 nm is the intrinsic emitting property of[4]CF by spectra measurement.Our result strongly indicated that the bending mode of chain would the third mechanism of g-band formation after ketone and aggregates/excimers.The first OLED via fluorene-based strained semiconductor[4]CF spin-coated film from CHCl3 as active layer has been fabricated.And the electroluminescent（EL）spectra show the green emission at 508 nm with CIE coordinates of（0.25,0.52）at the 5.38 V（turn-on voltage）.And the OLED exhibits the maximum bright-ness of 878 cd/cm2 at 10 V with a maximum luminescent efficiency of 0.83 cd/A.To further insight into the strain effect of the active Raman mode in[4]CF,the Raman feature for[4]CF crystal sample was investigated.Compared with the corresponding linear oligomer,it is found that introducing the strain energy into the backbone can not only increase the intensity of the Raman shift peak,especially in the low frequency region,but also shift the frequency of the same vibration mode.In order to study memory performances of the strained organic semiconductor,a seirs of the floating gate OFET memories with[4]CF as charge trapping element and PS as tunneling element were fabricated.Compared with the pure PS dielectric layer of the device,the introduction of CF into the devices exhibit good non volatile memory performances.With increasing the doping concentration of CF in hybrid films,the storage window of the OFET memory is gradually widened under the negative gate voltage.When the doping ratio is 1:2,the device exhibited largest memory window,20.1 V.By endurance testing,the device showed stable programmed state and erased state,and the ON/OFF current ratio was over 104 during the endurance testing process.In summary,inducing the high strain into the molecule can change the electronic structure which is consist of of radial P orbits,causing the change of the molecular topology structure and photoelectric properties.these make the material disperse in PS polymer films more completely.It can increase the storage sites and improve the storage capacity of the devices.This kind of material has a potential to application in non-volatile memory device. |
