Aggregation induced emission and mechanochromism: Multi stimuli responsive fluorescence switching of assistant acceptor modulated phenanthroimidazoles

We have reported four mechanochromic materials namely, 4-(6,9-di(anthracen-9-yl)-2-phenyl-1H-phenanthro [9,10-d]imidazol-1-yl)-N,N-diphenylaniline (PIDPA-An), 4-(6,9-di (anthracen-9-yl)-1-(4-(diphenylamino) phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl) benzonitrile (CNPIDPA-An), N,N-diphenyl-4-(2-phenyl-6,9-di (pyren-1-yl)-1H-phenanthro [9,10-d]imidazol-1-yl)aniline (PIDPA-Py) and 4-(1-(4-(diphenylamino)phenyl)6,9-di(pyren-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)benzonitrile (CNPIDPA-Py) consist of triphenylamine and phenyl or 4-cyanophenyl at N1 and C2 positions, respectively and bulky fused aromatics at C6/C9 positions. These materials show excellent thermal stability and exhibit strong aggregation induced emission enhancement (AIEE). These materials exhibit high quantum yield in film and show reversible mechanofluorochromism under external pressure. The pristine PIDPA-An (422 nm), CNPIDPA-An (418 nm), PIDPA-Py (440 nm) and CNPIDPAPy (448 nm) emits blue light, on grinding of PIDPA-An (466 nm), CNPIDPA-An (452 nm), PIDPA-Py (496 nm) and CNPIDPA-Py (490 nm) show bluish-green emission and annealing of these materials reverts to blue emission. The quantum yield (%) of PIDPA-An/CNPIDPA-An/PIDPA-Py/CNPIDPA-Py are found to be 0.55/0.58/0.60/0.65 (pristine), 0.51/0.54/0.57/0.61 (ground) and 0.48/0.50/0.51/0.57 (annealing) under external face. The adopted design strategy opens up new way to develop efficient mechanochromic materials.