The invention is directed to a N,N-substituted guanidine compound or a salt or solvate thereof according to formula (1), R
1
RNC(NH)NR
2
R
3
, wherein R
1
is methyl and R
2
is hydrogen. R
3
is a organic group comprising a halogen and thiomethyl substituted phenyl group. R is an organic group comprising a substituted aryl group Z wherein the substituent group is —Y—R
4
, wherein Y is a heteroatom chosen from the group consisting of O, S and N and R
4
is a fluorinated organic group.