Context : Supernovae ( SNe ) offer a unique opportunity to study physical properties , small-scale structure , and complex organic chemistry of the interstellar medium ( ISM ) in different galaxies .

Aims : Interstellar absorption features , such as atomic and molecular lines as well as diffuse interstellar bands ( DIBs ) , can be used to study the physical properties of extra-galactic diffuse interstellar clouds .

Methods : We used optical high-resolution spectroscopy to study the properties of the ISM in the SN 2008fp host galaxy , ESO428-G14 .
The properties of intervening dust were investigated via spectropolarimetry .

Results : The spectra of SN 2008fp reveal a complex of diffuse atomic clouds at radial velocities in line with the systematic velocities of the host galaxy .
In addition , a translucent ( A _ { \mathrm { V } } \sim 1.5 mag ) cloud is detected at a heliocentric velocity of 1770 km s ^ { -1 } ( redshifted by 70 km s ^ { -1 } with respect to the system velocity ) .
This cold dense cloud is rich in dense atomic gas tracers , molecules , as well as diffuse interstellar bands .
We have detected both C _ { 2 } and C _ { 3 } for the first time in a galaxy beyond the Local Group .
The CN ( 0,0 ) band-line ratios are consistent with an excitation temperature of T = 2.9 \pm 0.4 K. The interstellar polarisation law deviates significantly from what is observed in the Galaxy , indicating substantial differences in the host dust/size composition .
No variations over a period of about one month are observed in any of the interstellar medium tracers .

Conclusions : The lack of variability in the extra-galactic absorption line profiles implies that the absorbing material is not circumstellar and thus not directly affected by the SN event .
It also shows that there are no significant density variation in the small-scale structure of the molecular cloud down to 100 AU .
C _ { 2 } is used to probe the cold diffuse ISM density and temperature .
Here we also use observations of CN in a distant galaxies , though for now still in a limited way , for in situ measurements of the cosmic background radiation temperature .